post-graduate research projects

CURTIN INSTITUTE OF RADIO ASTRONOMY

For Applicants Commencing Studies in 2019/20

POST-GRADUATE RESEARCH PROJECTS

ADIO ASTRONOMY Curtin’s Institute of Radio Astronomy (CIRA) offers relevant, practical, and forward-thinking postgraduate research training to advance your career in astronomy, space science, technology, physics, or engineering (in particular combinations of these disciplines).

CIRA is led by world-renowned experts in radio astronomy. Our students join a lively and deeply engaged group working with national (Australian) and international partners. We are deeply involved with the Murchison Widefield Array (MWA) radio telescope, SKA pre-construction design and development work, and are a major partner in both the International Centre for Radio Astronomy Research (ICRAR) and ARC Centre of Excellence for Astrophysics in 3D (ASTRO-3D). With a large number of collaborators and partners across Australia and internationally, we offer our students an international research experience.

This booklet highlights our current set of higher degree research projects suitable for commencement during 2018 & 2019. These projects cover a range of aspects of modern astronomy including observational astronomy, analytical astronomy, and radio astronomy engineering. Students will gain vital skills as part of their study with us including analysing huge datasets (often multi-wavelength), working in teams and collaborations, as well as communicating their results, both written (paper publication) and via presentations at major conferences. Depending on the focus of the student’s project, their research may include opportunities to develop skills with telescope proposals and observing at Australian and international facilities and supercomputing experience. Many of our projects are designed to develop expertise ready for the next era of radio astronomy, most notably the Square Kilometre Array (SKA).

We welcome enquiries from well-qualified applicants to develop research proposals as part of their formal application to study at Curtin University. To be eligible to apply you must have a strong background in physics, ICT, or electrical engineering, good communication skills (including excellent English language, both written and spoken) and be ambitious to complete a first-rate higher degree at our Institute.

More information about CIRA can be found at http://astronomy.curtin.edu.au and all potential applicants to Curtin University should consult http://futurestudents.curtin.edu.au/postgraduates/ for details on admission, funding and course details.

We look forward to hearing from you!

Professor Steven Tingay

CIRA Executive Director

All queries: [email protected]


mailto:[email protected]


Postgraduate Research Projects for commencement in 2019/20

Page Title Supervisor

5 Absolute flux density measurements of Southern Sky calibrator sources Dr Marcin Sokolowski 6 Accretion of planetary debris onto white dwarf stars Dr Adela Kawka 7 Advances in Antenna Array Theory Prof David Davidson 8 Blowing Bubbles with Exploding Stars Dr Natasha Hurley-Walker 9 Chasing Fast-spinning Pulsars with the First SKA-Low Precursor Dr Ramesh Bhat 10 CMB spectral distortion at low radio frequencies – radio background, first

stars, galaxies and the sources of first light!!!! Dr Nipanjana Patra

11 Constraining the continuum background of extragalactic origin by precision radio background measurements

Dr Nipanjana Patra

12 EoR foreground mitigation with the CRAM A/Prof Randall Wayth 13 Evolution of the Radio Population Across Cosmic Time Dr Nick Seymour 14 Extragalactic science from the Multifrequency Snapshot Sky Survey (MSSS) Dr Jess Broderick 15 Fast follow-up of long Gamma-Ray Bursts with the Murchison Widefield

Array Dr Gemma Anderson

16 Fast Radio Bursts A/Prof Jean-Pierre Macquart 17 Finding pulsars in high-time resolution images Dr Marcin Sokolowski 18 Finding the Pressure Points of the Galaxy Dr Natasha Hurley-Walker 19 From Low-frequency Pulsar Observations to Interstellar Holography Dr Ramesh Bhat 20 GLEAM-X: Exploring the Universe in Radio Colour Dr Natasha Hurley-Walker 21 HI absorption in high-z radio galaxies Dr Natasha Hurley-Walker 22 High-Speed High-Accuracy Noise Parameter Measurement in the SKA-Low

Band Dr Adrian Sutinjo

23 Hunting the Elusive Black Holes in Star Clusters A/Prof James Miller-Jones 24 Interplanetary Weather Forecasting with the Murchison Widefield Array Dr John Morgan 25 Investigating the ionosphere's impact on the polarised radio sky Dr Christene Lynch 26 KM3NeT: studying neutrinos in the ocean depths Dr Clancy James 27 Looking for low radio-frequency afterglows of GRBs in the MWA data

archive Dr Marcin Sokolowski

28 Lunar Observing with the MWA Dr Benjamin McKinley 29 Lunar-Orbiting Radio Array Simulations Dr Benjamin McKinley 30 Managing the Complexity of Low-Frequency Radio Telescope Station Array

Model and Reality Dr Adrian Sutinjo

31 Mapping sky brightness temperature at low radio-frequencies (50-300 MHz) using the Engineering Development Array (EDA)

Dr Marcin Sokolowski

32 Mapping the magnetic field structure of white dwarfs Dr Adela Kawka 33 Measurement of brightness temperature of the Moon using the

Engineering Development Array Dr Marcin Sokolowski

34 Metamaterials for radio astronomy engineering Prof David Davidson 35 Monitoring low-frequency radio sky for transients Dr Marcin Sokolowski 36 Newly catalogued sources at low radio frequencies: high-redshift radio

galaxies? Dr Jess Broderick

37 Opening a window on the ionised interstellar medium of nearby galaxies Dr John Morgan 38 Particle physics beyond the LHC: what can cosmic rays tell us? Dr Clancy James

39 Powerful Black Holes Accreting at Extreme Rates Dr Gemma Anderson 40 Probing Fast Radio Bursts on nanosecond timescales A/Prof Jean-Pierre Macquart 41 Pulsar Science with the FAST and the First SKA-Low Precursor Telescopes Dr Ramesh Bhat 42 Radio Flares from Massive Magnetic Stars Dr Gemma Anderson 43 Rapid Follow-ups of Fast Radio Bursts with the MWA Dr Ramesh Bhat 44 Real-time radio imaging of black hole jets A/Prof James Miller-Jones 45 Resolving Pico-arcsecond Structures in Relativistic Plasmas Around Pulsars Dr Ramesh Bhat 46 Search for Terrestrial and Extraterrestrial Technosignatures with the MWA Dr Ian Morrison 47 Searching for bound supernova remnants Dr Adela Kawka 48 Searching for evidence of feedback in Centaurus A Dr Benjamin McKinley 49 Searching for Fast Radio Burst counterparts with the Transiting Exoplanet

Survey Satellite (TESS) Prof Steven Tingay

50 Searching for merged stars in the white dwarf population Dr Adela Kawka 51 Searching for optical transients with the Desert Fireball Network Dr Paul Hancock 52 Searching for Primordial Black Holes as Dark Matter Dr Nick Seymour 53 Searching for the First Black Holes with the MWA Dr Nick Seymour 54 Searching for the origin of magnetic fields in white dwarf stars Dr Adela Kawka 55 Shedding further light on a cosmic manatee at low radio frequencies Dr Jess Broderick 56 “The A-Team”: Low-frequency Observations of the Brightest Radio Galaxies

in the Southern Sky Dr Natasha Hurley-Walker

57 Silicon monoxide masers towards evolved stars Dr Christopher Jordan 58 The abundance patterns of metal poor stars in the Milky Way Dr Mahavir Sharma 59 The environments of the most distant radio galaxies Dr Jess Broderick 60 The Evolution of Black Holes Across Cosmic Time Dr Nick Seymour 61 The explosive outbursts of black holes A/Prof James Miller-Jones 62 The Impact of Proto-clusters on Radio Galaxies Dr Nick Seymour 63 The ionization bubbles in the early Universe Dr Mahavir Sharma 64 The time domain radio sky from SKA-Low prototypes A/Prof Randall Wayth 65 Towards more realistic MWA simulations using OSKAR Dr Jack Line 66 Uncovering Southern-sky Pulsars with a Next-generation Low-frequency

Radio Telescope Dr Ramesh Bhat

67 Using the Five hundred metre Aperture Spherical Telescope to detect the highest energy cosmic rays

Dr Clancy James

68 Verification and Measurement of Noise Coupling in a Low-Frequency Radio Telescope

Dr Adrian Sutinjo

5

Absolute flux density measurements of Southern Sky calibrator sources

To fully exploit the scientific capabilities of the Murchison Widefield Array (MWA), and the upcoming low-frequency component of the Square Kilometer Array (SKA-Low), astronomers need a set of calibrator sources with accurately measured flux densities. The number of bright calibrator sources in the Southern Hemisphere is very limited. Therefore, sources of moderate flux densities have to be used in order to correctly calibrate flux density scale in sky images from the aforementioned low radio-frequency instruments. Perley & Butler 2017 extended their flux-density scale down to approximately 50 MHz based on their recent measurements with the Karl G. Jansky Very Large Array (VLA). Their flux scale includes several primary calibrator sources for the MWA and SKA. However, there is a need for more accurately measured flux density calibrators measured over the entire frequency band 50 - 350 MHz of the SKA-Low telescope. Moreover, we would like to develop a method to measure flux density of any source in an absolute way (without the need to calibrate/bootstrap using earlier measurements).

The absolute flux scale measurements are critical for future instruments such as the SKA in order to be able to accurately measure flux densities of the observed sources. This project aims in developing a technique of performing absolute flux-scale measurements by using the Engineering Development Array (EDA; Wayth et al. 2017) and absolutely calibrated total power radiometer BIGHORNS (Sokolowski et al, 2015). We would like to apply this technique to measure flux-densities of multiple low-frequency Southern Sky calibrators over the entire frequency range of the SKA-Low (50 - 350 MHz). As the first step flux-densities of the calibrator sources measured by Perley & Butler (2017) would be performed in order to verify the method and compare the newly measured flux-densities with the existing flux scale. The method would then be applied to a larger set of sources. Finally, we would like to extend the method to be applicable to the upcoming SKA-Low telescope.

Figure 1: Engineering Development Array (EDA) at the Murchison Radio-astronomy Observatory. Right : BIGHORNS total power radiometer enabling calibration of flux densities in the absolute units.

Research FieldRadio Astronomy/Engineering Project Suitability PhD, Honours / Masters Project SupervisorDr Marcin [email protected] Co-Supervisors Assoc. Professor Randall [email protected]

http://adsabs.harvard.edu/abs/2017ApJS..230....7P

http://adsabs.harvard.edu/abs/2017PASA...34...34W

http://adsabs.harvard.edu/abs/2015PASA...32....4S

6

Accretion of planetary debris onto white dwarf stars

Many stars within our Galaxy host planets. Since the majority of stars end their lives as white dwarfs we want to know what happens to these planets as the star evolves and becomes a white dwarf. Up to now no planets have been found around white dwarfs however there is evidence that planets survive but as debris disks.

Elements heavier than helium are expected to sink and disappear below the atmosphere of a white dwarf, leaving either a pure hydrogen or helium atmosphere. However, a significant fraction of white dwarfs shows the presence of heavy elements such as calcium, magnesium and iron which means that they must have been accreted from material around the white dwarf. The discovery of polluted white dwarfs with large infrared excess tell us that this environment is a debris disk composed of asteroidal/planetary material.

The project will involve extracting, reducing and analysing mid- and high-resolution spectra of white dwarfs from the archives of the European Southern Observatory, which operates several 4m to 8m optical telescopes in the Chilean Atacama Desert. These spectra will be fitted with model spectra to determine the white dwarf atmospheric properties such as the effective temperature, surface gravity and abundance of heavy elements. Finally, the measured abundance pattern will be used to determine the likely source of the accreted material.

Figure 1: Artist’s impression of a debris disk around a white dwarf (Credit: NASA/JPL-Caltech)

Research Field Stellar Astrophysics

Project Suitability Honours 3rd Year, Summer

Project Supervisor Dr Adela Kawka [email protected]

Co-Supervisors

7

Advances in Antenna Array Theory

The Square Kilometre Array (SKA) project is an international effort to build the world’s largest radio telescope, with eventually over a square kilometre (one million square metres) of collecting area. SKA-LOW, the low frequency component of the Square Kilometre Array radio telescopes, will be deployed on the Murchison Radio-astronomy Observatory (MRO) in Western Australia. Our engineering team is currently working on the analysis and simulation of this pioneering system. It will consist of a large array of essentially dipole-like radiators, clustered into “stations” of 256 antennas.

Contemporary array theory leverages computational electromagnetic simulation, in particular generating embedded element patterns, from which key system parameters can be evaluated, determining the efficacy of the system. Additionally, these patterns may be required for regular system calibration. The accuracy of the computation of these patterns has never been comprehensively investigated, and this is a key component of this research project, with a particular focus on the impact thereof on radio telescopes comprising aperture arrays.

The key aim of this project is to advance methods for evaluating and ensuring the accuracy and reliability of CEM simulations, in particular for array simulations and SKA-Low. This will be achieved through a combination of numerical experimentation, mathematical analysis and experimental validation.

Figure 1: The AAVS1 prototype on the MRO. (Photo: DB Davidson).

Research Field Engineering

Project Suitability PhD

Project Supervisor Prof David Davidson [email protected]

Co-Supervisors Dr Adrian Sutinjo (TBC)

8

Blowing Bubbles with Exploding Stars

When a massive star uses up its hydrogen fuel, it rapidly undergoes collapse and then a violent explosion, known as a supernova. The outer layers of the star are cast off into space, creating an enormous rapidly-expanding bubble of bright X-ray and radio emission. This “supernova remnant” persists for ~one million years after the star has exploded. Simulations and star counts predict that there should be thousands of these remnants dotting our Milky Way galaxy, but only a few hundred are known, often the younger, brighter, and smaller objects. Where are the other remnants? What are we missing?

The Murchison Widefield Array (MWA) is a low-frequency radio telescope operated by an international consortium headed by Curtin University. This telescope was used to survey the whole sky, producing the GaLactic and Extragalactic All-sky MWA survey1. The wide bandwidth of the survey, across 72–231 MHz, allows us to determine the difference between thermal (blue in Fig. 1) and non-thermal (red/orange in Fig 1.) emission, and thus extract the SNRs from the images very easily. In these radio images, we found 27 of the “missing” SNRs, mostly older, larger, and dimmer sources than had been found before. However, the resolution of GLEAM was low, and this made it difficult to discriminate some sources against the confusing background of our Galaxy and find small or very faint SNRs. A new survey, GLEAM-X, has double the resolution, and five times the sensitivity. Observations have already been taken, and processing time secured on supercomputers at the Pawsey Centre.

Aims of project: 1) Transform the visibility data of the GLEAM-Xsurvey in the region of the Galactic Plane into well-calibrated images across a wide frequency range;2) Combine the data with existing GLEAM images tohighlight extended emission;3) Search the resulting images for previously-undetected SNRs;4) Obtain follow-up/ancillary observations with X-ray,spectral line, and/or pulsar searches to betterunderstand the astrophysics of these sources.

Requirements: This project is suited to a student with a strong grounding in astrophysics and an interest in learning low-frequency data reduction, including bash scripting and python programming. The data volumes are large so organisation skills are essential.

1 See this TED talk: http://bit.ly/nhwted

Research Field Radio Astronomy/Astrophysics

Project Suitability PhD Masters

Project Supervisor Dr Natasha Hurley-Walker [email protected]

Co-Supervisors

Fig1. Top: SNR G24.1+0.3, a newly detected SNR from GLEAM, surrounded by other known SNRs and confusing Galactic emission. Bottom: The 27 new SNRs detected using GLEAM.

http://bit.ly/nhwted

9

Chasing Fast-spinning Pulsars with the First SKA-Low Precursor

Pulsars are proven laboratories for advancing fundamental physics; those with spin periods of the order of a few to several milliseconds – the so-called millisecond pulsars – are particularly promising for a wide variety of science. Their clock-like stability can be exploited for applications ranging from detecting gravitational waves to probing the state of ultra-dense matter. As such, doing fundamental physics with pulsars is a headline science theme for the Square Kilometre Array (SKA) telescope, e.g. making a direct detection of nanoHertz gravitational waves isa key science driver for the Phase 1 SKA.

Pulsars are generally brighter at radio frequencies below 300 MHz, in which Australia’s Murchison Widefield Array (MWA) operates. The MWA is an official Precursor for SKA-Low, i.e. the low-frequency component of the SKA. However, finding fast-spinning pulsars at low frequencies poses several major challenges. In particular, traditional approaches involving tiling large areas of the sky and searching through thousands of pencil beams become computationally prohibitive. The large field-of-view and interferometric advantages of the MWA, along with its unique capability to record high-time resolution data from large parts of the skies at once, bring some exciting prospects to circumvent these formidable challenges.

This project will leverage a number of recent advances uniquely applicable to low-frequency wide-field interferometric arrays like the MWA. For example, implementing the hybrid approach of semi-coherent de-dispersion (Bassa et al. 2017) to process high-time resolution voltage time series data from the MWA will enable achieving optimal detection sensitivity to short-period pulsars. Furthermore, image-based techniques can be employed for efficient identification of promising pulsar candidates. These strategies will help accelerate the process of discovery and confirmation of pulsars, their rapid sky localisation and detailed characterisation. A demonstrable success in this area will bolster the prospects of SKA-Low to emerge as an efficient pulsar discovery machine.

Left: an artist’s impression of a fast-spinning (millisecond) radio-emitting pulsar, in binary orbit with a white-dwarf companion star. Right: MWA detection of a pulsar that spins at a rate of 456 times per second.

Research Field Observational Pulsar Astronomy

Project Suitability PhD Masters Honours

Project Supervisor Dr Ramesh Bhat [email protected]

Co-Supervisors Willem van Straten (Auckland) Jason Hessels (ASTRON)

#

CMB spectral distortion at low radio frequencies – radio background, first stars, galaxies and the sources of first light!!!!

The Cosmic Microwave Background (CMB) i.e. the relic radiation from the Big Bang is the oldest electromagnetic radiation in the Universe. CMB has been precisely measured by the COBE/FIRAS instrument between 30-600 GHz and it is shown to be a thermal blackbody at a 2.725K. Since then, various ground, space-based and balloon-borne experiments measured the CMB temperature covering the frequency range of 0.4 to 600GHz. At frequencies lower than 400 MHz the CMB temperature measurement is increasingly difficult due to instrumental complexity and galactic and extragalactic radiation that are at least 3 orders of magnitude brighter than the CMB. However, at these frequencies, in the absolute temperature spectrum of the CMB, hidden is the answer to one of the most important question of the cosmology: how and when did the first sources of light come to exist.

Below 200 MHz, the CMB is expected to deviate from its blackbody temperature of 2.725K and exhibit a specific spectral signature that resulted from the interaction between the CMB photons with the primordial neutral hydrogen at very early times, even before the first sources of light began to form. This is known as the redshifted 21cm signal, detection of which is one of the biggest challenges of present-day cosmology. When detected, it will provide a information about the early Universe, structure formation, nature of the first sources and evolution history of the Universe. Detection of the 21cm signal is identified as the science priority in various decadal surveys. Over a dozen experiments attempted to detect the redshifted 21cm signal using the single element radio telescope over past decade with only two producing any data of scientific significance.

This project will make a precision all-sky radio background measurement between 30-150MHz to detect the redshifted 21cm spectral signature in the CMB. It is a unique opportunity to build and deploy a second generation, single element radio telescope leveraging a vast number of recent developments in instrument design and data analysis. Resulting publications will be in the field of engineering, science and computation. It is particularly suitable for someone with an inclination to experimental radio astronomy, especially with a solid background in Electrical/ Telecommunication/Computer Science Engineering, Experimental Physics/Astrophysics. A good organizational skill, mathematical aptitude and some programming expertise in any language is desired.

Research Field Engineering, Observational Cosmology, Radio Astronomy


Thesis Supervisor Dr Nipanjana Patra [email protected]

Co-Supervisors A/Prof Randall Wayth [email protected]

The CMB blackbody temperature measured by various experiments at discrete frequencies. Between 20-200 MHz, the CMB temperature is expected to deviate from its blackbody temperature of 2.725K and take certain spectral shape known as the 21cm signal. This spectral shape depends on the evolution history of the Universe. A representative form of such deviation is shown in this figure.

Right : SARAS radio telescope – a precursor to the proposed work located at the Gouribidanur radio observatory, India : a single element radio telescope purposed developed to detect the redshifted 21cm signal by precision radio background measurements. Left: HYPERION – an interferometer designed and developed at the UC Berkeley and initially deployed at the Caltech’s Owen’s Valley Radio Observatory to detect theredshifted 21cm signal by precision radio background measurements. The proposed project is a continuation of this work.

11

Constraining the continuum background of extragalactic origin by precision radio background measurements.

Experiments that aim to detect the redshifted 21cm signal do so by making precision radio background measurements at low frequencies. These measurements also produce a volume of information on all-sky averaged galactic and extragalactic radio continuum which is yet not studied in detail. A purported detection of the redshifted 21cm signal in 2018 stirred in a controversy on whether there exist an excess radio background of extragalactic origin. This project will develop a method and correspondingalgorithm to separate the isotropic and anisotropic components in the all-sky radio background data. The isotropic part, being of extragalactic origin can provide an upper limit on the volume averaged emissivity of the extragalactic radio source population. This will be compared with the currently available radio source-counts from various radio surveys and estimates from the diffused all-sky maps and will address the question whether there exists an excess extragalactic isotropic radio background. The work would involve generating simulated dataset for testing the method as well as real data from earlier observations.

Following the development of the foreground separation method, we would study the effect of foreground modelling on the detectability of the redshifted 21cm global signal. As a result of foreground separation, a part of the 21cm signal is always lost. Such signal loss will not only reduce the chances of a 21cm detection but also can render a false detection and/or distorted cosmic history. We will investigate the possibility of detecting the redshifted 21cm global signal in the presence of signal loss due to radio background modelling. This project also has the potential to be converted into a Ph.D thesis.

This project is most suitable as a Master’s thesis with a solid background in Computer/Data Science, Telecommunication engineering, physics and astrophysics, maths. A good coding efficiency in any language, (preferably in python and/or in C) is needed. A part of this work may also be offered as a 6 month’s project for domestic or international students who wish to work as interns provided the student can make funding arrangements for themselves.

Research Field Cosmology, Radio Astronomy Project Suitability Masters, Internship Thesis SupervisorDr Nipanjana Patra [email protected] Co-Supervisors A/prof Randall Wayth [email protected]

Left: A simulated data set showing the radio continuum background measured by a single element radio telescope over 24 hours. Right: The isotropic component isolated from the radio background data using the initial algorithm which will be developed further as a part of this project.

12

EoR foreground mitigation with the CRAM

Bright radio galaxies near to the horizon imprint contaminating structure in datasets for the Epoch of Reionisation experiment with the Murchison Widefield Array (MWA). The EoR experiment aims to measure fluctuations in the neutral hydrogen brightness temperature from the first billion years of the Universe. This exceptionally weak signal is masked by foreground radio galaxies and Milky Way Galaxy, which are orders of magnitude brighter.

The CRAM-tile (Central Redundant Array Mega-tile) is a new large MWA tile (8x8 dipoles) that sits within the centre of one of the redundant sub-arrays of the MWA (4x4 dipoles). Its size means that it measures the sky with a smaller primary beam size compared with the normal MWA tiles. This project will use data from the CRAM to help develop foreground removal techniques for the MWA EoR program, using simultaneous data acquisition on redundant MWA-MWA and MWA-CRAM baselines.

Aims of project (dependent on length of program)

(i) Characterise the CRAM tile primary beam response

(ii) Compare observations from redundant MWA-MWA and MWA-CRAM baselines

(iii) design and test methods for using the datasets to remove contaminating signal from the MWA EoRdata.

This project can be tailored for single year (Honours) to three-year (PhD) programs, and would suit a student with interest in signal processing, data analysis and computing.

CRAM tile, installed in 2018-2019 at the Murchison Radio-astronomy Observatory (credit: A. McPhail)

Research Field Radio Astronomy/Engineering

Project Suitability Masters/PhD Honours

Project Supervisor A/Prof Cathryn Trott

Co-Supervisors A/Prof Randall Wayth Dr Jack Line

13

Evolution of the Radio Population Across Cosmic Time

Radio surveys are powerful tools for tracing the evolution of star forming galaxies and their central super-massive black holes across cosmic time. The radio luminosity of a galaxy is a measure of either its star formation rate or the power of the jets from the super-massive black hole. This project will utilise data from the plethora of cutting edge radio surveys conducted by Australian based facilities such as the Murchison Widefield Array, the Australian Square Kilometre Array Pathfinder and the Australian Telescope Compact Array. The radio sources from these surveys will then be cross-matched with multi-wavelength surveys such as the Galaxy and Mass Assembly (GAMA) survey in order to identify their host galaxy.

This project will include:

(i) processing and conducting some of the radio observations in these surveys, and becoming an expertin radio interferometry,

(ii) cross-matching with GAMA to identify the host galaxies of these radio sources and determine theredshift and nature the of these sources,

(iii) calculate the global evolution of star forming galaxies and black hole jet activity as a function of lookback time,

(iv) use these observations to constrain models of galaxy and black hole evolution.

This project will uniquely exploit the broad frequency coverage of Australian radio telescopes and pave the way for deeper radio surveys with the Square Kilometre Array.

Fig 1. Greyscale optical image of the galaxy Messier 99 overlaid with radio surveys of different frequencies and resolution. The radio emission is arising from the star formation in its spiral arms.

Research Field Radio Astronomy

Project Suitability PhD Honours

Project Supervisor Dr Nick Seymour [email protected]

Co-Supervisors Dr Minh Huynh

http://www.mwatelescope.org/

http://www.atnf.csiro.au/projects/askap/index.html

https://www.narrabri.atnf.csiro.au/

https://www.narrabri.atnf.csiro.au/

http://www.gama-survey.org/

14

Extragalactic science from the Multifrequency Snapshot Sky Survey (MSSS)

The Multifrequency Snapshot Sky Survey (MSSS; Heald et al. 2015, A&A, 582, A123) was the first northern sky survey carried out at low radio frequencies (below 250 MHz) with the Low-Frequency Array (LOFAR), a pan-European radio telescope with its core located in the Netherlands. With a competitive combination of bandwidth, sensitivity, and angular resolution, MSSS will facilitate novel science in areas such as supernova remnants and HII regions, nearby galaxies, pulsars, radio transients, and extended objects such as giant radio galaxies, clusters and relics. It will also have significant legacy value in the scientific literature: in combination with the GLEAM-X survey from the upgraded Murchison Widefield Array (MWA) in Australia, an all-sky, low-frequency catalogue at a resolution of an arcminute and better will be possible.

In anticipation of a first public data release, the MSSS team is conducting a variety of quality control checks on the data products. You will play an important role in these efforts by analysing a selection of large-area (200 square degrees), multi-band (119-158 MHz) mosaics that cover the entire northern sky. Not only will key metrics be assessed, but given that each mosaic is expected to contain up to 1000 radio sources, you will have the exciting opportunity to carry out scientific studies on a selection of interesting, and indeed sometimes unusual objects (e.g. see Stewart et al. 2016, MNRAS, 456, 2321; Clarke et al. 2017, A&A, 601, A25 and figure below; Chyzy et al. 2018, A&A, 619, A36). In this project, the science focus will be on extragalactic sources, such as, for example, the aforementioned giant radio galaxies, clusters and relics, as well as other potential topics such as high-redshift radio galaxies and compact steep-spectrum sources.

Figure: MSSS has resulted in the discovery and detailed study of a new 2.56 Mpc giant radio galaxy associated with a disturbed galaxy group (UGC 9555). This image illustrates the huge extent of radio emission, stretching larger on the sky than the full moon. LOFAR contours are displayed in white, and the NVSS 1.4 GHz survey in red. The inset shows the host galaxy group. Lime green contours from the 1.4 GHz FIRST survey show compact radio emission from the AGN and its jet. Coloured contours are smoothed bands from the Sloan Digital Sky Survey (SDSS), indicating the disturbed nature of the group that hosts this interesting radio source. Further details can be found in Clarke et al. 2017 (A&A, 601, A25).


Project Suitability Honours Masters

Project Supervisor Dr Jess Broderick [email protected]

Co-Supervisors Dr George Heald (CASS)


15

Fast follow-up of long Gamma-Ray Bursts with the Murchison Widefield Array

Long Gamma-Ray Bursts (GRBs) occur either when a massive star goes supernova to form a black hole. Over a short period of time, a huge amount of material is accreted onto a newly formed black hole and a very powerful jet of gamma-rays is launched into space. For a small fraction of these events, the jet is aimed toward the Earth where it can be detected by gamma-ray satellites such as Fermi and Swift. These space missions then send immediate alerts to a network on the ground, allowing telescopes such as the Murchison Widefield Array (MWA) to rapidly begin observing the event.

The MWA is a low frequency (80-300 MHz) radio telescope operating in Western Australia and the only operational Square Kilometre Array (SKA)-Low precursor telescope. The MWA is an entirely electronically steered instrument, meaning that it can ‘slew’ to any part of the sky nearly instantaneously. The MWA also has an extremely large field of view. The large field of view and fast slew time means that the MWA is uniquely placed to provide the fastest follow-up radio observations of transient (explosive or outbursting) events, including GRBs.

For the last 5 years, the MWA has been automatically responding to GRBs detected by the Fermi and Swift satellites, obtaining 30 minutes of observations following each outburst. There are now over 700 observations in the database that are being processed, and even more are being taken all the time. An automated pipeline is in place to download and process all these data and make the required images.

In this project you will analyse radio images to look for signs of prompt radio emission generated by GRBs – something that has never been seen before at low radio frequencies. Such a detection would directly aid our understanding of the central engines of the most powerful explosions in the Universe. This project will help build your programming and time management skills, and will allow you to work on the Pawsey supercomputers.

A massive star undergoing core-collapse to produce a brief jet of gamma-rays. As the jet breaks through the material left by the dying star there is a flash of radiation detectable at radio wavelengths. This radio flash is yet to be detected (credit: Wikipedia).



Project Supervisor Dr Gemma Anderson [email protected]

Co-Supervisors Dr Paul Hancock

16

Fast Radio Bursts

They are bursts of radio waves from space that are over in a blink of an eye. They are variously attributed by hard-nosed and self-respecting physicists to everything from microwave ovens, to the accidental transmissions of extraterrestrials making their first baby steps in interstellar exploration. The remarkable properties of these Fast Radio Bursts (FRBs) have so enthralled astronomers that, in the decade since their discovery with the Parkes radio telescope, more theories have been advanced to explain them than new bursts have been detected. FRBs are remarkable because they are outrageously bright yet appear extremely distant. As far as astronomers can tell, they come from a long way away – half way across the observable Universe or more! Because of that, whatever makes FRBs must be pretty special – unlike anything astronomers have ever seen.

The field is currently grappling with the most fundamental questions about these events:

• What is their spectrum?• What is the brightness distribution?• Do FRBs represent one-off cataclysmic explosions, or do they repeat?• What is their event rate?• How distant are these events?

Relatively few FRBs are still known. However, the Australian SKA Pathfinder has now nearly doubled the population of known FRBs, and is now rapidly increasing the sample further. In this project you will work with other members of the Commensal Real-Time ASKAP Fast Transients (CRAFT) team to examine the properties of FRBs and help understand what causes them. CIRA is a key member of the CRAFT survey on the Australian SKA Pathfinder (ASKAP), which is currently detecting Fast Radio Bursts at a high rate, and which will soon be able to localise the bursts to 1” on the sky. We are offering several projects in this field: 1. Searching for repeating FRBs in ASKAP data

Unlike previous FRB surveys, ASKAP constantly monitors the same patches of sky for FRBs. Hence,the region of sky in which any FRB is detected will have been observed many times. Here you willsearch the ASKAP data at the locations and dispersion measures of known FRBs to look for faint burstsby examining the statistical properties of the noise.2. Characterising the spectral features of ASKAP FRBs

ASKAP FRBs show mottled structure across the band. What does this mean? Is this due tointerstellar scintillation, or can you show that it is an intrinsic property of the FRB emissionmechanism?

3. The FRB dispersion measure distributionThe dispersion measures (DMs) of FRBs represent a means to probe the ionized Inter-GalacticMedium, the repository of over half of the Universe’s baryonic (normal) matter. But how do weinterpret the DM? In this project you would investigate how the DM distribution depends onvariations in the distribution of matter along individual sight-lightsthrough the IGM.

The scope exists to expand any one of these projects into a PhD.

(right) FRB 170107, the first Fast Radio Burst detected by ASKAP. To date, over 30 FRBs have been found by CRAFT.


Project Suitability

Honours

Project Supervisor A/Prof Jean-Pierre Macquart [email protected]

Co-Supervisors Dr Ramesh Bhat Dr Clancy James

17

Finding pulsars in high-time resolution images

Since their discovery over 50 years ago, pulsars have been one of the most intriguing astrophysical phenomena. They are extremely dense objects, built primarily of neutrons (and thence called neutron stars), rotating at rates of up to hundreds of times per second and emitting a beacon of radio emission. The physical mechanisms causing the radio emission still remains to be understood. The full list of pulsar-related discoveries is long; for instance, pulsars have proven as very powerful laboratories for testing Einstein’s general relativity, as probes of the interstellar medium and as precise clocks for prospective future detections of low-frequency gravitational waves, and finally the very first extrasolar planets were discovered in a pulsar system. So far over 2500 pulsars have been discovered in our Galaxy. However, the total number of pulsars is expected to be much larger (and not all can be observed from Earth due to their radio beacons not pointing in our direction).

The main goal of this project is to develop and apply image-based techniques for finding new pulsar candidates in high-time resolution imaging data obtainable from low radio-frequency aperture array instruments such as the Murchison Widefield Array (MWA; Tingay et al 2013). These data have been collected in the high-time resolution mode, using the so-called Voltage Capture System (VCS) mode. They can be used to form high-time resolution ( < 1 second ) images, which can be searched for candidate sources in a variety of ways.

The main goal of this project is to develop suitable algorithms for searching Stokes images (in the I,Q,U,V polarisations) for variable sources, and ranking them by degree of polarisations (pulsars tend to be polarised sources), spectral steepness, and variability properties, in order to select the most promising pulsar candidates for further follow-up observations (with the MWA or high frequency radio telescopes such as Parkes, the GMRT or others). The method has also potential for finding other types of radio transients (including Fast Radio Bursts). With its wide field of view (of the order of 20o x 20o) and extremely radio-quiet location, the MWA is an ideal instrument to develop and test such new techniques of discovering pulsars with low radio-frequency aperture array instruments. The success of these methods would make them directly applicable for pulsar searches planned with the upcoming the Square Kilometre Array (SKA) telescope, which will offer one to two orders of magnitude higher sensitivity, thereby enabling substantially more efficient pulsar and transient searches.

Figure 1. An example of de-dispersed 0.5-second images of pulsar J0837-4135 (left) without a pulse, and (right) with a pulse detected illustrating how transient sources like pulsars can be identified in high-time resolution MWA images.

Research Field Radio Astronomy Project SuitabilityHonours / Masters / PhD Project SupervisorDr Marcin [email protected] Co-Supervisors Dr Ramesh Bhat [email protected]

http://adsabs.harvard.edu/abs/2013AJ....145...23M

18

Finding the Pressure Points of the Galaxy

The low-frequency Square Kilometre Array (SKA) is being built here in Western Australia. This new instrument will transform our understanding of the role of the cold, atomic gas in galaxy evolution. The main tracer of this gas is neutral hydrogen (HI) but measuring this does not constrain the physical properties of the gas (e.g. pressure, density). By observing carbon recombination lines (CRRLs) at frequencies less than 350MHz we can study the physical conditions of diffuse, cold clouds within our Galaxy. Using the Murchison Widefield Array to do this is important in pathfinding toward the SKA.

Context: The interstellar medium (ISM) is a collection of stellar ejecta and stellar nurseries. Cold, diffuse, atomic clouds are a key component of the ISM and contains a large fraction of ionized carbon (C+). This attracts free electrons, causing a cascade to lower energy levels and emitting radio waves at specific frequencies: “radio recombination lines”, detectable by radio telescopes. The frequency of the emission is directly related to the size of the carbon atom, such that recombination lines detected at around 10MHz are the size of a virus; 1000 times the size of what can exist on Earth.

These large atoms are very sensitive pressure probes of gaseous environments. If the gas is too dense, larger atoms cannot exist as the outer electrons are sheared off the outer shell. At frequencies less than 100MHz these CRRLs are detected in absorption against strong continuum. At frequencies greater than ~150MHz the CRRLs are detected in emission. However, in between these two frequencies the CRRLs will null as the competing emission mechanisms balance, but the exact frequency at which this happens is highly dependent of the gas density in the region observed.

Aims of project: Honours: the interested student will utilise existing MWA data cubes or generate new cubes from existing scripts. The data are from the Phase II (extended baseline) MWA and will either study the region around the Vela Supernova Remnant or Orion Molecular Cloud. Masters or PhD: As above, and additionally: prepare scientific publications on the results, propose observations on the Long Wavelength Array linked with the Karl Jansky Very Large Array at 50—80MHz to examine low-frequency CRRLs, and investigate the implications for SKA surveys.

Requirements: This project is suited to a student with a strong grounding in astrophysics and a good understanding of or willingness to learn statistics so that these sensitive measurements may be made in a robust and quantitative way. The project will also involve low-frequency data reduction, statistics and large-scale data processing on supercomputers, so organisation and computing skills are also useful.


Project Suitability PhD, Masters, Honours


Co-Supervisors Dr Chenoa Tremblay [email protected]

Figure 1: Image of Vela Supernova Remnant, RCW38 star forming region and Puppis taken at 114MHz with the Murchison Widefield Array. This region is currently being surveyed for molecular lines with long integration times.

19

From Low-frequency Pulsar Observations to Interstellar Holography

Pulsars make fabulous tools as probes of the interstellar medium (ISM) of our Galaxy. Their radiation is pulsed, spatially coherent and highly polarised – a combination which enables their signals to carry imprints of the ionised, turbulent and magneto-ionic properties of the media through which they propagate. At low radio frequencies (i.e. longer wavelengths), these effects are significantly magnified as a result of their strong dependencies with the observing frequency.

Multipath propagation through the ISM gives rise to a rich variety of observable effects, many of which can be meaningfully used to study the small-scale structures in the ISM. For decades, possible investigations were limited to the use of more traditional scattering and scintillation techniques, which are generally useful for a statistical characterisation of the ISM along the pulsar’s sight line. Deflected parts of the radiation may also occasionally give rise to subtle features in the secondary spectra of pulsar scintillation (e.g. parabolic arcs; Figure 1), and these can be exploited to pinpoint the location of turbulent plasma or probe any anisotropy that is present (e.g. Bhat et al. 2016, 2018). The physical origin of these arcs is an active area of research, with a multitude of recent interpretations involving hot stars or plasma sheets (Walker et al. 2017; Simard & Pen 2018; Gwinn 2019). Another notable development is the application of cyclic spectroscopy (Demorest 2011), and phase-retrieval algorithms that enable coherent de-scattering; i.e. simultaneous recovery of the pulsar’s intrinsic signal and the ISM delay structure (Walker et al. 2013).

This project will capitalise on new instrumentation and capabilities that are being developed for pulsar observations with the Murchison Widefield Array (MWA), which enable signal reconstruction at a very high time resolution (of the order of microseconds). Developing related instrumentation and the signal processing techniques, and exploiting them for novel pulsar science will form the central theme of the project. This includes accurate characterisation of signal distortion caused by the ISM (important for high-precision timing) and holographic reconstruction of the interstellar microstructure (at resolutions unattainable by other techniques). The project involves close collaboration with Manly Astrophysics.

Fig 1: Dynamic scintillation spectrum of the millisecond pulsar J0437-4715 (left) and its secondary spectrum (right), from MWA observations (Bhat et al. 2018). Faint parabolic arc-like features arise from the deflected parts of pulsar’s scattered radiation. The indicated delays (~microseconds) will be directly measurable using the new capabilities and the advanced techniques that will be realised through this project..


Project Suitability Honours Masters PhD

Project Supervisor Dr Ramesh [email protected] Co-Supervisors Willem van Straten (Auckland)Mark Walker (Manley)

20

GLEAM-X: Exploring the Universe in Radio Colour

The Murchison Widefield Array (MWA) is a low frequency (80 — 300 MHz) radio telescope operating in Western Australia and the only SKA_Low precursor telescope. One of the largest science programs for the MWA is the GaLactic and Extragalactic All-sky MWA (GLEAM) survey, which has surveyed the entire visible sky for two years since the MWA commenced operations.

A large part of the 0.5 PB of GLEAM data has been published as an extragalactic source catalogue (see figure), and work is ongoing to publish deeper fields of some areas, and the Galactic Plane. Observations of GLEAM-X have commenced, using the newly-upgraded MWA, which now has double the resolution, allowing images 10x deeper to be created, potentially revealing millions of new radio sources over the next few years.

Combining the datasets will create the most sensitive survey output from the MWA ever. As well as generating images and catalogues that are widely useful, the student will also undertake a focussed research project that utilises the data. This could include (but is not limited to): transient/variable radio sources, scintillation, the ionosphere, and continuum studies on objects such as radio galaxies, galaxy clusters, supernova remnants, and pulsars. The project is well suited to a student with strong computing skills, an interest in gaining a deep understanding of radio astronomy calibration and imaging, and an interest in a science area that can be addressed by data from the survey.

Fig 1: The first year of GLEAM observations, covering the whole Southern Sky. This is the first radio colour view of our universe: find out more via this TED talk: http://bit.ly/nhwted .



Project Supervisor Dr Natasha Hurley-Walker [email protected] Co-Supervisors TBD

http://bit.ly/nhwted

21

HI absorption in high-z radio galaxies

Before the very first galaxies formed, the Universe was a sea of hydrogen and helium, gently cooling and collapsing. When the first galaxies formed, they ionised the surrounding gas, turning it from an opaque absorbing cloud into the transparent, ionised plasma we see today: this time is called the Epoch of Reionisation.

This change will have occurred at different rates in different locations in the Universe. When we look at high-redshift galaxies which emit in the radio spectrum, any neutral hydrogen along the line-of-sight will absorb the characteristic HI line at that redshift. For the highest-redshift galaxies, this HI line is shifted from 1.4GHz down to ~150MHz. This is within the frequency range of the Murchison Widefield Array, a radio telescope operated by Curtin University and based in the Murchison Radio Observatory.

This project aims to detect HI absorption in high-redshift radio galaxies using the MWA. As this is a spectral line experiment, it requires a unique data processing pipeline and careful control of calibration and systematics. There are several candidate radio galaxies on which first studies could be made, and once a pipeline is developed and detections made, the project can expand to include other high-z candidates currently being identified from the GaLactic and Extragalactic All-sky MWA (GLEAM) survey. There are thousands of hours of data already taken on several fields which would be suitable for this search. This project is designed to synergise with the project “The First Black Holes with MWA”.

Fig 1: The Universe ionises, transforming froma sea of opaquq hydrogen into the complex structures we see today.




Co-Supervisors Dr Elizabeth Mahony (CSIRO) Dr James Allison (Oxford) Dr Nick Seymour

22

High-Speed High-Accuracy Noise Parameter Measurement in the SKA-Low Band

The Low-Frequency Square Kilometre Array (SKA-Low) spans the frequency band from 50 MHz to 350 MHz, which is a 7:1 bandwidth. In the past, the noise generated by the low-noise amplifier (LNA) connected to each receiver has been assumed to be uncorrelated with one another. However, research in the past decade has shown that the noise emanating from the LNAs is radiated through the antenna and is received by the neighbouring antennas. This effect creates a bias in the correlation matrix produced by the radio telescope.

Such bias can potentially be corrected if the bias can be quantified. This involves electromagnetic modelling as well as measurement of the LNA itself. This project concerns the latter; that is the characterization of the LNA in the SKA-Low band. Curtin Institute of Radio Astronomy (CIRA) has experience, expertise and the equipment to make accurate measurements at this frequency band.

This project focuses on the use of the impedance tuner to make this measurement (see figure). CIRA operates a specialized low-frequency impedance tuner which covers 100 MHz to 1 GHz. Recently, we have developed a technique to use the tuner reliably below its lowest frequency rating. We have also discovered a method to cover the 7:1 band using only a few tuner positions. The objective of this project is to apply this technique to noise parameter extraction of SKA-Low prototype LNAs or similar demonstrators. This includes automation, verification, uncertainty calculation and refinement of the technique for speed and accuracy.

Research Field Radio Astronomy Engineering

Project Suitability MPhil/ Honours

Project Supervisor Dr Adrian Sutinjo [email protected] Co-Supervisors Dr. Budi Juswardy Mr. Daniel Ung

23

Hunting the Elusive Black Holes in Star Clusters

Globular star clusters are old, dense clusters of stars, containing up to millions of stars within a volume of space only a few light years across. Because of their old age, these clusters are expected to harbour thousands of black holes formed from the very first stars that were born, evolved, and turned into black holes in the cluster. As the cluster is extremely dense, some of these black holes then might entrap other stars in the cluster and form a binary star system. We would see them as they release energy by pulling matter from the trapped star. However, there have been very few black holes actually found in globular clusters so far, making it a puzzle as to what happens to the black holes formed in clusters. Do they get ejected from the cluster? Or are they hiding in the cluster but just difficult to observe?

We have been conducting a survey of Galactic globular clusters, hunting black holes – among other unusual systems that can be formed in clusters as a result of encounters between stars in these dense environments. With this survey, we have so far been able to discover new black hole candidates in several clusters in the Milky Way. We are now following up on some of these candidates to estimate their properties (e.g., how massive is the black hole? How much matter is the black hole pulling from the trapped star?), and also focusing on finding new black holes. Furthermore, our survey has allowed us to discover and study other unusual types of binary systems in clusters like neutron stars that are pulling matter from a trapped star, some of which are able to launch powerful radio jets. This has provided a unique opportunity for us to study how neutron stars can pull matter from a trapped star in a dense star cluster and produce energetic jets.

The aims of this projects are: • Search for new candidate black holes or neutron star binary star systems in archival and new

data (Radio + X-rays).• Reduction and analysis of archival and new multi-wavelength data (radio, infrared, optical, X-

rays) on candidates in globular clusters to determine their nature.• Determine the population of black holes/neutron stars in globular clusters based on results.

With this project, we hope to achieve a better understanding of what happens to black holes in star clusters.

Left: Globular cluster 47 Tuc, one of the largest clusters in our Galaxy. We recently discovered a black hole in this cluster that is in a very tight orbit with a white dwarf. Right: Artist’s impression of a binary stellar system in which a black hole has trapped another star and feeds off the material from the star.

Research Field Accretion physics


Project Supervisor A/Prof James Miller-Jones [email protected]

Co-Supervisors Dr Arash Bahramian

24

Interplanetary Weather Forecasting with the Murchison Widefield Array

Our society is heavily reliant on infrastructure such as power grids and Satellite Navigation Systems. However a major Space Weather event such as those that occurred in the 19th century and the first half of the 20th century could place these technologies at risk. In fact it has been estimated that the cost of a Carrington-like event could be 1 trillion USD. Consequently, predicting the severity of such events in advance is a hugely important topic.

Just as stars twinkle in the night sky, compact radio sources twinkle due to turbulence in the solar wind, a phenomenon known as interplanetary scintillation (IPS). This technique is useful both for studying compact radio sources, and for making measurements of the solar wind. The latter will be the focus for this project, with a particular focus on using MWA IPS observations to detect Coronal Mass Ejections (CMEs).

We have a quarter of a Petabyte(!) of observational data consisting of ~1000 observations taken in the first half of 2016 when the Sun was relatively active. We believe that there should be 185 Coronal Mass Ejections detectable within this data.

The initial phase of the project will be to reduce this huge amount of data (or a large subset of it), and determine what major events are detected within it. The next phase will to connect as many events as possible to Coronal Mass Ejections detected by other instruments (primarily LASCO), and also detected via in-situ measurements in Earth Orbit and elsewhere. The expectation is that not all MWA events will have been detected previously, and that the MWA measurements will be able to significantly refine our understanding of how the ejections evolved as they moved away from the Sun.

As well as working with the huge archive of existing data there will also be the opportunity to make new observations with the MWA, and developing creative ways to use the instrument to detect and track space weather.

You will also have the opportunity to work with an international network of collaborators across East Asia, India, the US and Europe, as well as more locally with CSIRO.


Project Suitability PhD/Masters Honours

Project Supervisor Dr John Morgan [email protected]

Co-Supervisors

1 A CME detected by the MWA. Each point is a scintillating source and stronger scintillation indicates denser solar wind. The CME can be seen as an increase in scintillation equidistant from the Sun.

25

Investigating the ionosphere's impact on the polarised radio sky

The formation of the first luminous sources and their subsequent reionisation of the intergalactic medium, called the Epoch of Reionization (EoR), was a pivotal period in the history of the Universe. The most promising method to observe the EoR is via tomography of the redshifted 21 cm line of neutral hydrogen. Due to the expansion of the Universe, 21 cm emission from the EoR redshifts to radio frequencies between 100 – 200 MHz. Detecting this cosmic signal is a goal for current and next generation low-frequency radio telescopes.

A significant challenge to radio EoR experiments is identifying and removing foreground emission produced by a variety of astronomical sources. The most significant contributor to astrophysical foregrounds is emission from the Milky Way Galaxy. This emission is polarised, and as it propagates through the interstellar medium, the emission becomes spectrally complex via an effect called Faraday rotation. Imperfect calibration of the telescope response can cause this polarised spectral structure to leak into total intensity emission and either obscure or mimic the EoR signal.

Yet the Earth's ionosphere may attenuate the amount of polarised foreground emission we expect to observe with the Murchison Widefield Array (MWA). The ionosphere is a turbulent region of the Earth’s upper atmosphere, permeated by the Earth’s magnetic field and ionised by Solar radiation. Changes in the total electron content of the ionosphere impart positional shifts of background astronomical sources and additional Faraday rotation. EoR experiments will average over a variety of different ionospheric Faraday rotations. This averaging has the potential to de-polarise Galactic foreground emission.

So far, the MWA EoR experiment has focused on the impact of the ionospheric positional shifts but has yet to investigate the effect of the variable ionospheric Faraday rotation thoroughly. The goal of this project is to: (1) characterise the activity of the ionosphere via calculations of the ionospheric Faraday rotation expected in the MWA EoR observing fields, and (2) explore the connection between ionospheric Faraday rotation and positional shifts previously observed using the MWA, to help identify best ionospheric conditions for the MWA EoR experiment.

Figure: Polarised emission (not corrected for ionospheric Faraday rotation) from the Milky Way Galaxy, observed at 216 MHz using the MWA. By averaging over variable ionospheric conditions, this emission may become de-polarised. Figure is from Lenc et al. 2017, PASA, 34, e040.


Project Suitability Honours

Project Supervisor Dr Christene Lynch [email protected]

Co-Supervisors Dr Chris Jordan A/Prof Cathryn Trott

26

KM3NeT: studying neutrinos in the ocean depths

KM3NeT is a cubic kilometre experiment being constructed at the bottom of Mediterranean Sea. It is designed to detect neutrinos – almost massless subatomic particles – using the flashes of light they give off when they interact. By detecting them, KM3NeT will study the origin of the highest-energy particles in nature – cosmic rays – and resolve a long-standing question of particle physics, the neutrino mass hierarchy.

The Curtin Institute of Radio Astronomy is collaborating with the European consortium constructing KM3NeT. Neutrino telescopes primarily look downwards, through the Earth – and so KM3NeT sees the same sky as in Australia. Our aim is to identiy the astrophysical events producing the neutrinos KM3NeT detects, be they hypernovae, accreting black holes, neutron star mergers, or something as-yet unknown. Several projects are available in ‘multimessenger astronomy’, using astronomical expertise to study proposed cosmic ray/neutrino sources, and understanding how to use KM3NeT to search for them. The predecessor of KM3NeT, ANTARES, has been operating for ten years, and its data are available for developing analysis methods to be used with KM3NeT.

The key aims of the project will be:

(i) Understand how KM3NeT detects neutrinos, and how to reconstruct their properties

(ii) Develop tests of neutrino production in astrophysical sources

(iii) Apply these searches to first data from KM3NeT phase 1, and archival data from ANTARES

Projects targeting particle physics, such as searches for supersymmetry and charm-meson decay, are also available.

Successful applicants will be expected to travel to Europe to attend collaboration meetings, and be willing to spend a one-month exchange at collaborating institutes (e.g. in Italy, Spain, Netherlands, France, and/or Germany), as appropriate to the project. They should also be prepared to collaborate with expert astronomers from radio, optical, and other backgrounds, as required for astrophysical modelling.

Simulation of a neutrino event in KM3NeT. The neutrino interacts to produce a muon (thick beige line) which travels through KM3NeT, producing Cherenkov light (thin coloured lines; cone indicates shock front). This light is detected by KM3NeT optical modules (circles). The time (blue: early, red: late) and magnitude (size of circles) of the photon signature can be used to reconstruct the original neutrino’s energy and direction.

Research Field Multimessenger astrophysics


Project Supervisor Dr Clancy [email protected] Co-Supervisors Prof Steven Tingay

27

Looking for low radio-frequency afterglows of GRBs in the MWA data archive

Gamma-ray bursts (GRBs) are one of the most violent and energetic explosions observed in the Universe. They release energies of the order of 1053 - 1054 ergs in the intervals ranging from fraction of a second (short GRBs) up to several hundreds of seconds (long GRBs). They were serendipitously discovered during the Cold War era (specifically 1960s) by the VELA satellites monitoring the space for possible violations of nuclear ban treaty. Instead they discovered an entirely new astrophysical phenomena. Since then, several thousands of GRBs were discovered by a few generations of satellites dedicated to study these astrophysical processes (BeppoSAX, CGRO, HETE, Integral, Swift, Fermi and Polar). Their counterparts in optical, radio and other electromagnetic wavelengths have been observed including the recent observation of gravitational wave event GW170817 accompanied by a short (< 1 second) GRB 170817A. GRBs are truly one of the most fascinating astrophysical processes (Abbott at at, 2017).

They are expected to produce low-frequency radio afterglows which could potentially be observed months or even years after the GRB explosions (when the GRB ejecta collides with the interstellar medium surrounding the progenitor ). However, so far there has been no observational evidence of these predictions. This project aims in establishing existence or non-existence of GRB afterglows within the limitations of the Murchison Widefield Array (MWA; Tingay et al 2013) sensitivity. The main goal is to take advantage of large data archive from the MWA and the corresponding calibration database in order to search for low radio-frequency counterparts of the known, archive GRBs which can be found in the databases of the several satellite missions detecting GRBs. The idea is to analyse as many GRBs as possible, which have multiple MWA observations over the span of several years.

The potential positive detection of the first low radio-frequency afterglows of GRB would be a very important discovery. Alternatively, if there are no positive detections the upper limits can be derived, which given the known estimates of GRB energies and other characteristics, can lead to conclusions on the surroundings of the GRB progenitors. Such an analysis can lead to extension of this project even to a PhD level.

Figure 1. Observation (black filled data points) and modelling (solid or dotted curves) of lightcurve of radio afterglow of GRB 030329 by van der Horst et al (2008). Empty triangles in the right-bottom image at 325 MHz represent 3 sigma upper limits (non-detection


Project Suitability Honours (as appropriate) / Masters / 4th year with potential to be extended to a PhD

Project Supervisor Dr Marcin Sokolowski [email protected]

Co-Supervisors Dr Gemma Anderson [email protected] Dr Paul Hancock [email protected]

http://adsabs.harvard.edu/abs/2017ApJ...848L..12A


28

Lunar Observing with the MWA

Little is known observationally about the period in the early Universe between when the first stars formed and when the Universe was completely ionised by radiation from stars, galaxies and active black holes. Our group here at the Curtin Institute for Radio Astronomy is attempting to learn about this epoch by observing the 21-cm radiation emitted by neutral hydrogen, which has been redshifted by the expansion of the Universe to metre wavelengths. To achieve this, we use the Murchison Widefield Array (MWA) telescope - an interferometer consisting of 256 antenna tiles, tuned to low radio frequencies (including both the FM radio and digital TV bands), situated in the West Australian outback, about 800 km north-east of Perth.

In this project, we aim to measure the all-sky signal from neutral hydrogen, using the Moon as a thermal reference source. This is a novel technique that relies on imaging the Moon with the MWA across a wide band from 70 to 230 MHz. The thermal radiation from the Moon, however, is corrupted by reflections from radio transmitters on Earth and emission from relativistic electrons in our own Galaxy. Couple this with the fact that different radio wavelengths penetrate to different depths in the lunar regolith, and you have a very challenging experiment.

Depending upon the interests and skills of the student, the project could be tailored to include: interferometric calibration and imaging, computer modelling of reflected terrestrial transmissions (earthshine), separation of earthshine from the Moon’s thermal emission, modelling and removal of Galactic foregrounds and extraction of the faint cosmological signal from multiple epochs of observations. There are a lot of data already collected and waiting to be processed, offering a great opportunity to learn how to do exciting science with a low-frequency radio interferometer.



Project Supervisor Dr Benjamin McKinley [email protected]

Co-Supervisors A/Prof. Cathryn Trott [email protected]

Dipole antennas in a single tile of the MWA telescope. Superimposed on the background is a radio image of our Galaxy (and the Moon!)

29

Lunar-Orbiting Radio Array Simulations

The future of radio astronomy is on the Moon! For a long time, radio astronomers have dreamed of placing a low-frequency radio telescope on the far side of the Moon, where it would be completely shielded from earth-bound interference, and unaffected by the ionosphere. As a step toward this ambitious goal, several projects are now planning to send radio arrays into lunar orbit, where they would observe while on the far side and transmit data back to Earth while on the near side of their orbits. This potentially opens an entirely new parameter space of ultra-long wavelength, high angular resolution radio imaging that is impossible from the surface of the Earth.

To make such a mission a reality, detailed simulations of the orbiting array and new imaging and calibration strategies will be required. Researchers at the Curtin Institute of Radio Astronomy are collaborating with Chinese colleagues to produce such simulations and build software that can be used to produce images from lunar-array data. We are looking for students to join the project in order to:

(i) realistically simulate the science-data output of the satellites

(ii) develop and test new calibrationstrategies for the array

(iii) develop and test imaging algorithms that can be applied to this data set

This is a unique opportunity to become involved with a space mission and to collaborate with Chinese researchers on an ambitious project to observe the Universe like never before!




Co-Supervisors A/Prof. Cathryn Trott [email protected]

An artist’s impression of a lunar-orbiting array against the background image of our Galaxy at low frequencies

30

Managing the Complexity of Low-Frequency Radio Telescope Station Array Model and Reality

The Low-Frequency Square Kilometre Array (SKA-Low) operating from 50 MHz to 350 MHz is envisaged to comprise 512 stations each of which consists of 256 pseudo-randomly located antennas. Accurate knowledge of the station beam and its receiver noise property is essential to successful astronomical imaging and observation. The more sensitive the observation, the higher the demand placed on the knowledge of instrumental effects. For brevity, we henceforth refer to the station beam and its receiver noise property as the station model.

Although the knowledge and tools exist to model the properties of the SKA-low station, they are only an approximation of reality. It is impracticable to expect that every detail of the deployed station be recorded and computed for each station as the simulation time becomes prohibitively long. The objective of this project is to devise a method to manage the tension among the required model accuracy, simulation time, deployment impairment and component tolerances. Dish-based radio astronomy appears to have a widely-accepted handle on this problem through smoothness tolerance and verification method both in the laboratory and in the field. Such a consensus seems to be missing in low-frequency radio astronomy.

The aim of this project is to fill this gap by developing a clear, actionable and measurable guideline for low-frequency station realization. Initially, we will study high-precision dish-based radio telescopes such as ALMA and glean key similarities and differences to low-frequency telescope. Based on this, we will divide the low-frequency problem into modules each with a well-defined interface which takes into account understanding of modelling and measurement constraints. The end result is an SKA-low station beam model and verification guideline with clear connection and distinction to high-performance and well-accepted radio telescopes.


Project Suitability PhD Honours (as appropriate)

Project Supervisor Dr Adrian Sutinjo [email protected] Co-Supervisors Prof. David Davidson A/Prof. Randall Wayth

31

Mapping sky brightness temperature at low radio-frequencies (50-300 MHz) using the Engineering Development Array (EDA)

To fully exploit the scientific capabilities of the Murchison Widefield Array (MWA), and the upcoming Square Kilometre Array (SKA), astronomers need an accurate model of the large-scale structure of the low-frequency sky. Current models1 are largely based on the monochromatic 408-MHz observations made by Haslam et al. in 1981.

This project aims to dramatically improve the sky model by mapping the brightness temperature of the sky across a wide bandwidth of 50 to 300 MHz, using the Engineering Development Array (EDA; Wayth et al. 2017) or another SKA precursor station. The EDA is a SKA station consisting of 256 bow-tie dipoles (identical to those used by the MWA). The EDA has a narrow primary beam of the order of a few degrees, complementary to the original observations by Haslam et al. This should enable brightness temperature mapping with reasonable accuracy, with potential to improve the resolution by utilising oversampling techniques. The calibration of the EDA data has already been proven using observations of bright radio sources such as Hydra A and 3C444.

Figure 1. Haslam 408 MHz Map (Haslam, et al., 1982)

Figure 2. Engineering Development Array (EDA) at the Murchison Radio-astronomy Observatory

1de Oliveira-Costa et al. 2017; http://space.mit.edu/home/angelica/gsm/


Project Suitability Masters, Honours, PhD


Co-SupervisorsAssoc. Professor Randall [email protected]

http://adsabs.harvard.edu/cgi-bin/bib_query?1982A&AS...47....1H



http://adsabs.harvard.edu/abs/2008MNRAS.388..247D

32

Mapping the magnetic field structure of white dwarfs

White dwarfs represent the final stage of stellar evolution for the majority of stars and they provide one the most sensitive probes into the history of stellar formation in the Milky Way due to their predictable cooling rates. A significant fraction of these stellar remnants harbours a magnetic field ranging from a few 100 G up to several 100 MG and it can affect the evolution and atmosphere structure of the white dwarf, as well processes such as accretion flows. The origin of magnetic fields in white dwarf stars remains unknown. Currently two leading theories have been proposed to explain the presence of magnetic fields in white dwarfs. The first is the fossil field origin, which means that the white dwarf has inherited the magnetic field from its progenitor, which is usually assumed to be a magnetic peculiar A and B star (Ap and Bp star). However, this scenario fails to explain the paucity of magnetic white dwarfs in close but non-interacting orbit with low-mass main-sequence stars. This leaves magnetic cataclysmic variables without direct progenitors, and as a result, a second origin was proposed. In this second scenario, a magnetic field is created within binary systems, either during a common envelope phase or in the merger of two white dwarfs. The two theories predict different magnetic field structures and rotational velocities. A study of the strength of the magnetic field, its surface structure and whether it is correlated with the white dwarf mass and/or cooling age will provide clues to the origin of the magnetic field. To understand the origin of magnetic fields and the role it plays in white dwarf atmospheres and evolution, we must first know the field strength and structure.

The European Southern Observatory (ESO) operates several 4m to 8m optical telescopes in the Chilean Atacama Desert which provides the best observing conditions on Earth. These telescopes are equipped with state-of-the-art instruments covering a vast range of the electromagnetic spectrum from the near ultraviolet and optical to the infrared. Therefore, ESO provides the ideal tools that are needed to carry out detailed studies of white dwarf stars.

The aim of this project will be to study the magnetic field structure of white dwarfs known to show variability in photometry, spectroscopy or spectropolarimetry. You will calculate magnetic model spectra

and develop fitting programmes to find a unique solution to the field structure through mapping the magnetic field on the surface of the white dwarf. The model spectra will be compared to photometric, spectroscopic andspectropolarimetric data. Since Australia has access to 8m class telescopes of the ESO and its vast range of instruments, this project will primarily use data obtained with ESO.

Figure 1: Artist’s impression of stellar magnetic field lines (Credit: ESO/L. Calcada)

Research Field Stellar Astrophysics Project Suitability PhDHonours Project SupervisorDr Adela [email protected] Co-Supervisors A/Prof James Miller-Jones

33

Measurement of brightness temperature of the Moon using the Engineering Development Array

The brightness temperature of the Moon (T_moon) is not well known at low radio-frequencies (<300 MHz). Such a measurement would provide a valuable input into the lunar occultation technique of the global Epoch of Reionisation (EoR) measurement. The lunar occultation method of the global EoR measurement has been developed for Murchison Wide-field Array (MWA; Tingay 2013) and LOFAR. However, T_moon is a relatively poorly constrained parameter in the modelling.

The goal of this project is to test the feasibility of measuring the brightness temperature of the Moon using the Engineering Development Array (EDA;Wayth (2017)) or other precursor station of the Square Kilometre Array (SKA). The EDA is the precursor station of the SKA radio-telescope consisting of 256 bow-tie dipoles (same as used by the MWA). The EDA with its very narrow primary beam (of the order of a few degrees) should enable brightness temperature mapping of the Moon with a reasonable accuracy (oversampling techniques might be necessary to improve the resolution). The calibration of the EDA data has already been tested by observations of bright calibrators (HydA or 3C444).

Figure 1 Engineering Development Array (EDA) at the Murchison Radio-astronomy Observatory


Project Suitability Honours (as appropriate) / 4th year / Masters

Project Supervisor Dr Marcin Sokolowski [email protected] Co-Supervisors Dr Benjamin McKinley [email protected]


http://adsabs.harvard.edu/abs/2015MNRAS.450.2291V


34

Metamaterials for radio astronomy engineering

Metamaterials are artificially engineered materials with electrical and magnetic properties not occurring in nature at radio frequencies – examples include “double negative” materials, with negative permittivity and permeability. These have been used in the theoretical development of transformation optics for electromagnetic cloaking, which has been demonstrated experimentally for some special geometries.

The aim of this project is to investigate the use of metamaterials for realizing new concepts in antenna elements for low-frequency radio telescopes, such as SKA-Low and other concepts. One line of investigation will focus on dense, regular arrays where strong mutual coupling complicates the design of wideband antenna arrays.

The application of metamaterials is an important topic in contemporary antenna engineering in general and this project overlaps strongly with many other applications of antennas in telecommunications, defence etc.

Figure 1: A split-ring resonator, part of a metamaterial array. Credits: NASA, public domain.

Research Field Engineering

Project Suitability MSc or PhD

Project Supervisor Prof David Davidson [email protected]

Co-Supervisors Dr Adrian Sutinjo (TBC)

https://upload.wikimedia.org/wikipedia/commons/8/82/Split-ring_resonator_array_10K_sq_nm.jpg

35

Monitoring low-frequency radio sky for transients

Although low-frequency (<400 MHz) radio sky is not reported to be highly variable in terms of transient objects, there have been increasing number of transients detections by new low-frequency instruments. Sensitivities of the existing instruments are not high enough to detect all (or at least many) of the low-frequency counterparts of transients detected at higher electromagnetic energies (up to gamma-rays). However, there have been several recently reported low-frequency transient detections. Such as for example detection of the outburst of the black hole candidate X-ray binary MAXI J1348-630 at 154 MHz and 216 MHz with the Murchison Widefield Array (MWA) by J. Chauhan et al (2019) or detection of a very bright

transient (> 800 Jy) of unknown nature by the LongWavelength Array (Varghese, S. et al (2019)). Hence,although the abundance of low-frequency radio transientsis small there are events (including some of unknownnature) which can be observed at low radio-frequencies.

This project aims to develop tools for automatic identification of transients in the MWA data. Over the last two years many observations of calibrator sources were reduced, calibrated and imaged in order to develop a database of calibration solutions for the MWA, specifically for the All-Sky Virtual Observatory (ASVO). Hence, there is a large set of images of the calibrator fields which could be analysed in search for transients as a first and minimal step of the project (Honours / 4th project / Summer Student level).

The project can be extended further to enable near-real time reduction, imaging and transient search of MWA observations collected daily by the telescope (for instance create a few images per each observed field), which can also be easily imaged using the earlier mentioned calibration database (daily updated with new calibration solutions). Finally, the next extension would be to perform all-sky scans with the MWA every few months in order to monitor sky variability on a few-month timescale ( pilot observations have been collected and a new proposal for future observations is being prepared ). All these efforts will aim towards a real or near-real time transient detection system for the upcoming low-frequency component of the Square Kilometre Array (SKA-Low) including all-sky images from the precursor stations (AAVS1 or EDA).

Research Field Engineering / Radio Astronomy

Project Suitability Honours (as appropriate) / Masters other 1 year projects with possible extension into a PhD


Co-Supervisors Dr Jess Broderick [email protected] Assoc. Professor Randall Wayth [email protected]

http://adsabs.harvard.edu/abs/2019ATel12520....1C

http://adsabs.harvard.edu/abs/2019ApJ...874..151V

36

Newly catalogued sources at low radio frequencies: high-redshift radio galaxies?

The latest generation of low-frequency radio surveys (below about 250 MHz; e.g. Heald et al. 2015, A&A, 582, A123; Hurley-Walker et al. 2017, MNRAS, 464, 1146; Intema et al. 2017, A&A, 598, A78; Shimwell et al. 2019, A&A, 622, A1) have already catalogued hundreds of thousands of sources. However, some of these sources were not seen before in corresponding higher-frequency radio surveys, and hence are newly catalogued. What are these objects?

First, why would a radio source be seen at lower frequencies only? One possibility is that it is variable, or a transient, and it was only detected because the low-frequency survey happened to be conducted when the source was ‘on’ and emitting electromagnetic radiation. Another possibility is that the radio source is detectable at low frequencies, but the flux density decreases rapidly as the observing frequency increases. Such sources are said to have an ultra-steep (USS) radio spectrum. An example is shown in the figure below, where a detection was made in a LOFAR map at 150 MHz (greyscale), but not in the higher-frequency WENSS (325 MHz; blue circles) and NVSS (1400 MHz; red circles) surveys.

A variety of radio source classes can be characterised by very steep spectra, for example rapidly spinning, millisecond pulsars found in our Galaxy. USS selection is also an efficient way of finding the most distant radio galaxies in the Universe: the so-called high-redshift radio galaxies (HzRGs; e.g. review by Miley & De Breuck 2008, A&AR, 15, 67). HzRGs are crucial tracers of massive galaxy formation in the early Universe but are rare objects. Could some of the newly catalogued sources be HzRGs?

In this project, you will use a selection of low-frequency survey data from both the Murchison Widefield Array (MWA) in Australia and the Low-Frequency Array (LOFAR) in the Netherlands, as well as additional multi-wavelength data, to start to uncover the true nature of these objects. How many could be distant galaxies, and how many are ’interlopers’ in the much more nearby Universe? How can we use multi-wavelength data to begin to build a classification scheme to more efficiently select the best HzRG candidates, especially when we will soon have catalogues comprising billions of galaxies in the era of the Square Kilometre Array (SKA)? This project will address these questions, and additional, related topics.



Project Supervisor Dr Jess Broderick [email protected] Co-SupervisorsDr Nick Seymour


37

Opening a window on the ionised interstellar medium of nearby galaxies

The ionised Interstellar Medium (ISM) is an important component of our Galaxy, comprising as much as 50% by volume and 80% by mass of the total ISM. It traces many astrophysical processes, and yet, due to the difficulty of observing it directly (compared with the neutral component, which can be studied via the 21 cm line) it is poorly understood. Very Long Baseline Interferometry (VLBI) observations allow the turbulence in the ionised ISM to be probed along lines of sight by measuring the “scatter broadening'” of intrinsically compact sources. However, there are great difficulties in determining the distribution of the ionised ISM from our position well within the plane: only within 1kpc of the Solar System can complex structure be mapped, allowing correlation with other astrophysical phenomena.

Applying this technique to other galaxies could produce significantly improved results since even a small inclination to the line of sight separates the components of the ISM, greatly increasing the observable information. A pilot study of M31 undertaken a few of years ago showed very promising results, with strong evidence of the detection of the ionoised ISM of a nearby galaxy for the first time. Much deeper VLBI observations of M31 have now been undertaken and await analysis.

Beyond the main goal measuring the ISM of M31 there are further secondary goals that might be achieved with these data. The first is HI absorption towards the brighter background sources, one of

which lies right on a neutral filament in the M31 galaxy. The second is determining accurately the brightness M31* across at least 3 epochs in 2012, when it is thought to be much dimmer than expected. Third, the possibility of detecting compact sources that are hosted within M31, such as X-ray binaries.

With future instruments, such as the SKA participating in observations, the number of lines of sight probing a galaxy such as M31 would be enormous. Planning for such observations could also form part of the project if the student is interested.

Fig: The angular size of sources (assumed to be intrinsically compact sources seen through the M31 galaxy as a function of angular distance from the core of M31. Those nearest to the centre appear to be larger. This is thought to be due to “scatter broadening” of the sources by the turbulent ISM of M31.



Project Supervisor Dr John Morgan [email protected]

Co-Supervisors A/Prof JP Macquart [email protected]

38

Particle physics beyond the LHC: what can cosmic rays tell us?

Cosmic rays are the highest-energy particles in nature, impacting the Earth with energies more than a million times higher than can be achieved with the Large Hadron Collider. As such, they hold the key to particle physics processes that cannot be studied in a laboratory.

When a cosmic ray interacts, it leads to a cascade of billions of secondary particles, which in turn emits a burst of radio waves lasting less than a microsecond – yet this burst holds unique information on the primary cosmic ray’s properties. And the world’s most sensitive radio telescope, the Square Kilometre Array (SKA), will soon begin construction here in Western Australia.

The High Energy Cosmic Particles Focus Group is an international collaboration aiming to use the SKA to study both the origin of cosmic rays, and high-energy particle physics processes. A prototype particle detector has been deployed at the Murchison Widefield Array (MWA) – the SKA-low precursor – and a cosmic ray detection mode with the MWA is being developed. It is therefore vital to understand exactly what the SKA could tell us about the standard model of particle physics – and beyond.

Aims of project:

(i) Model high-energy particle physics interactions

(ii) Determine the effects on cosmic ray signals

(iii) Determine how MWA/SKA data can be used to probe high-energy particle physics processes

This project will use a particle physics simulation package, CORSIKA, and its radio extension, CoREAS, to simulate high-energy particle physics cascades, the associated radio emission, and its detection by the SKA. An honours project would progress through aims (i) and (ii) only, while a PhD student would be expected to collaborate with the Institute for Theoretical Physics in Hamburg, Germany, and present their results at an international conference.

Simulation of the radio signal generated by a cosmic ray as seen by the core of the Square Kilometre Array, generated under standard physical assumptions. But what will deviations from this expectation tell us about physics at the highest energies? This project will tell us the answer.

Research Field Particle physics/radio astronomy


Project Supervisor Dr Clancy James [email protected]

Co-Supervisors A/Prof Tim Huege Karlsruhe Institute of Technology, Germany

39

Powerful Black Holes Accreting at Extreme Rates

The release of gravitational energy as mass is suddenly dumped onto a black hole powers some of the most explosive phenomena in the Universe. This is the most extreme example of a universal process called accretion, which is responsible for the growth of all astrophysical systems, from stars to galaxies. In this project, the student will seek to understand how black holes transform the material they consume into powerful outflows, and quantify how much energy these jets can carry away. You will study the most powerful black holes to probe how this process works at its most extreme limit known as the Eddington limit, selecting the most short-lived, explosive events to unveil how the process proceeds in real time. These include stellar-mass black holes rapidly consuming material torn off a binary companion star, known as transient ultraluminous X-ray sources (ULXs), and supermassive black holes tearing apart unlucky stars that wander too close, known as tidal disruption events (TDEs).

The unrivalled capabilities of the new X-ray telescope eROSITA, which is due to be launched in March 2019, will discover thousands of transient ultraluminous X-ray sources and tidal disruption events. The PhD student will be expected to perform and analyse follow-up radio observations of these rapidly-evolving systems using advanced radio telescopes including the Australian Telescope Compact Array (ATCA), the South African Square Kilometre Array (SKA) pathfinder telescope MeerKAT, and the SKA low frequency precursor the Murchison Widefield Array (MWA; based in Western Australia). Such observations will probe the powerful jets that are launched by these rapidly accreting black holes, allowing for real-time exploration of the connection between the infalling matter and the launching of jets in some of the most extreme environments known in the Universe.

Research Field Accreting Physics/Radio Astronomy


Project Supervisor Dr Gemma Anderson [email protected]

Co-Supervisors A/Prof. James Miller-Jones [email protected]

40

Probing Fast Radio Bursts on nanosecond timescales

Fast Radio Bursts are bright microsecond- to millisecond-timescale

events whose time-frequency characteristics prima facie indicate that

they emanate at cosmological distances. Their remarkable properties

have so enthralled astronomers that, in the decade since their discovery

with the Parkes radio telescope, over 50 theories have been advanced to

explain them! Recent work has now definitively confirmed that these

events do occur at cosmological distances, thus pushing the energetics

of their radio emission to the limits of our understanding. In short, we do

not understand the mechanism by which their ultra-luminous radio

emission – some twelve orders of magnitude greater than that observed

in radio pulsars – is produced. Neither do we understand what the

progenitors of these events are. Are they solitary neutron stars, black

holes, mergers of dense stellar systems, or something altogether

different?

In this project you will examine the properties of FRBs at ultra-high time resolution to investigate the origin of their outrageously luminous radio emission. You will take advantage of the Australian SKA Pathfinder’s (ASKAP’s) ability to both (i) interferometrically localise (to <1”) and (ii) measure the electric field signal associated with each radio burst at extremely high signal-to-noise (>60). The voltage-capture system on ASKAP enables us to measure the pulse intensity and polarization on time resolutions of 3 nanoseconds.

Voltage capture systems with other radio telescopes (e.g. UTMOST) have already revealed FRBs with astounding temporal structure on timescales of tens of microseconds (see Figure 1). But what does this structure signify, and how does it relate to the emission mechanism? Does the position angle of the linear polarization often observed in FRBs change during the pulse? Do the emission characteristics indicate that the system is rotating, like a pulsar?

You will work with other members of the Commensal Real-Time ASKAP Fast Transients (CRAFT) team to examine the properties of FRBs and investigate what produces their emission. The FRB team at CIRA is a key component of the CRAFT team, which is currently detecting FRBs at a high rate.

Figure 1: The remarkable temporal and spectral structure of FRB170827, reproduced from Farah et al. (2018). Several FRBs possess temporal structure on timescales as short as this.



Project Supervisor A/Prof Jean-Pierre Macquart [email protected]

Co-Supervisors Dr Clancy James

41

Pulsar Science with the FAST and the First SKA-Low Precursor Telescopes

Pulsars – i.e., rapidly-spinning neutron stars, produced by massive stellar explosions – are proven laboratories of nature for advancing fundamental physics. Those with spin periods of the order of a few milliseconds, or in compact orbits with another star, are particularly promising for a wide variety of science. Specifically, the clock-like stability of their pulse arrival times can be exploited for applications ranging from searching for ultra-low frequency gravitational waves to probing the state of ultra-dense matter. This array of exciting science is enabled by discoveries of exotic pulsars that allow us to probe new physics, in particular physics under extreme conditions, such as strong-field gravity, or matter at nuclear densities. Indeed, fundamental physics with pulsars is a recognised headline science theme for the upcoming Square Kilometre Array (SKA) telescope.

The unprecedented collecting area of the newly-built Five-hundred metre Aperture Spherical Telescope (FAST) in China makes it the most sensitive instrument to search for pulsars. This is vividly demonstrated by an increasing number of new discoveries and candidates that are emerging from early science projects with the FAST. On the other hand, the massively large field of view of the Australian Murchison Widefield Array (MWA) – hundreds of square degrees at frequencies 100-200 MHz – makes it an excellent survey instrument at low radio frequencies. High time resolution digital archives of the full southern sky will be produced by an all-sky survey program underway at the upgraded MWA, and these data can be readily mined for important confirmation and/or follow-up observations of new pulsar discoveries/candidates from the FAST. Similarly, potential pulsar candidates and discoveries from the MWA can be efficiently followed up using the high-frequency capabilities of FAST.

This project will capitalise on the unique, and highly complementary, capabilities of two major radio facilities, i.e. the FAST and the MWA, to undertake rapid follow-up and confirmation of promising pulsar candidates. Besides the prospects of discovering exotic pulsars in the large common skies of the two facilities, this will constrain the spectral, scattering and emission of properties of numerous pulsars, which is valuable to predict pulsar survey yields expected with SKA1-Mid and SKA1-Low.

The Five-hundred metre Aperture Spherical Telescope (FAST) in China (left) and Australia’s Murchison Widefield Array (MWA; right) have substantial common skies and contemporaneous sky visibilities, to enable some unique pulsar science.




Co-Supervisors Di Li (NAOC) George Hobbs (CASS)

42

Radio Flares from Massive Magnetic Stars

Stars with extremely strong magnetic fields (at least 100 times that of our Sun) can produce extremely powerful flares that are detectable across the electromagnetic spectrum, from the radio band and all the way up to X-ray and gamma-ray wavelengths. Our interest in studying such flares stems from our desire to learn how they physically and chemically impact planet formation and habitability. These studies also provide insight into magnetic reconnection processes that are far more extreme than those seen from our Sun. Historically, most low frequency flare star studies have targeted very low mass magnetic stars, such as M dwarfs, with the aim of tracing exotic processes associated with magnetic fields that produce nearly 100% circularly polarised (known as coherent) radio emission. However, recent low frequency studies conducted with the Giant Metrewave Radio Telescope (GMRT) at 610 MHz have detected similar coherent emission associated with massive magnetic stars (see Figure below). Such detections have huge implications on how strong magnetic fields effect the evolution and final supernova of massive stars.

For this project, you will use the Murchison Widefield Array (MWA) to study low frequency radio flares produced by massive, young and rapidly rotating magnetic stars that are destined to go supernova. These studies will form the basis of a new collaboration with GMRT observers. MWA observations collected between 100-200 MHz will be combined with GMRT observations taken between 300 MHz and 1.4 GHz in order to directly probe the transition between different low frequency, coherent emission mechanisms, and will be the first combined low frequency study of massive magnetic stars. Using these techniques to directly probe the magnetic fields in massive stars will allow us to understand the role they play in stellar explosions.

Figure – Left: Artist’s impression of flare star (Casey Reed/NASA), Right: GMRT detections of radio flares at 610MHz as a function of the rotation phase of the massive star HD 133880 (Das et al. 2018).

Research Field Radio Astronomy Project Suitability Honours Project SupervisorDr Gemma [email protected] Co-Supervisors Dr Paul Hancock

43

Rapid Follow-ups of Fast Radio Bursts with the MWA

In 2013, a team of astronomers conducting a large sky survey for pulsars with the Parkes telescope announced the discovery of an exciting new class of transient sources – Fast Radio Bursts (FRBs; Thornton et al. 2013). This landmark discovery triggered a world-wide hunt to find many more, with the recent breakthrough by the Canadian CHIME telescope marking a major milestone, i.e. ~100s of bursts detected down to ~400 MHz. These bursts are thought to originate from cosmological distances (~Gpc), and they are potential new probes for cosmology; e.g, to measure the baryonic content of the Universe, and the magnetic field of the Intergalactic Medium.

The physics governing the origin of these energetic bursts remains a mystery, despite a continuing flurry of theoretical ideas, including exotic possibilities including dark matter, and even cosmic strings; and even after their interferometric localisations at sub-arcsecond resolution. The plot further thickens with no burst emission seen to date at frequencies below ~300 MHz.

Prompt follow-up of FRBs is technically challenging due to their extremely short time durations (~ms). The co-location of the Australian SKA Pathfinder (ASKAP) telescope and the Murchison Widefield Array (MWA) was recently exploited (via shadowing) to circumvent this (Sokolowski et al. 2018), but the time resolution achievable is limited to ~500 milliseconds, which is not optimal given their short durations.

This PhD project will focus on the development and scientific exploitation of a major new capability that will allow high-time resolution trigger possible with the newly-commissioned voltage buffer mode of the MWA (Meyers et al. 2018). Along with the rapid-response observing mode that will soon be released, this will allow receiving and responding to the trigger alerts from facilities such as the ASKAP. This will enable unique science relating to the FRB emission physics, as well as their propagation and progenitor models, and thus will contribute to advancing our understanding of these mysterious sources.

Research Field Time-domain Astronomy

Project Suitability PhD Masters Honours


Co-Supervisors Dr Marcin Sokolowski A/Prof Jean-Pierre Macquart

Figure 1: FRB 110220 – one of the brightest FRBs discovered in the Parkes high time resolution Universe survey (Thornton et al. 2013). The burst’s dispersion measure of 945 pc cm-3 results in an arrival time spread of approximately 1100 milliseconds across the 400 MHz observing band of Parkes survey observations. The burst would have arrived at the MWA 185 MHz band approximately 112 seconds after its time of detection at Parkes. The inset shows the shape of the pulse, where an exponential tail resulting from multi-path scattering through the intergalactic medium is clearly visible, and follows the expectations based on a Kolmogorov-type turbulence.

44

Real-time radio imaging of black hole jets

Accreting black holes are known to launch powerful, relativistic jets that move away from the black hole at close to the speed of light. These jets provide a key source of feedback of energy and momentum to the surrounding environment. When a black hole is feeding sedately the jets are fairly steady, but when it accretes at higher rates the jets become more powerful but episodic, appearing as individual clouds of radio emission moving away from the black hole.

Using the technique of very long baseline interferometry (VLBI) we can zoom in on these powerful jets, tracking their motion as they move outwards. This technique involves combining the signals from multiple different telescopes separated by thousands of kilometres, and assembling an image from the combined data. This is the same technique recently used by the Event Horizon Telescope Consortium to take the first image of a black hole shadow, and can provide sufficient resolution for an observer in Perth to make out a coin located in Sydney.

At such high resolutions, the jets from nearby stellar-mass black holes can move significantly over the course of an observation, as well as brightening or fading. This violates the fundamental assumptions that go into imaging radio astronomical data (which assume a source that is constant over the timescale of the observation), and therefore requires new approaches. In one recent case, we split a four-hour observation up into two-minute chunks to observe the jets evolving in real time (as shown in the Figure). While this highly manual approach yielded new insights into the dynamics of the black hole jets, new imaging algorithms have recently been developed that could help to automate this process.

In this project, you will investigate the application of some of these new imaging algorithms to VLBI data on black hole X-ray binaries, aiming to provide higher-fidelity imaging of time-variable structures. This will allow you to extract new science from existing data sets, probing how jets evolve and propagate in real time. In cases where we can couple the time-variable jet behaviour to the changes observed in the inflowing gas around the black hole (as seen in the X-rays), we can aim to probe the universal link between accretion and ejection phenomena around black holes.

A montage of images showing the evolution of the radio jets in a stellar-mass black hole X-ray binary system, over a period of just 20 minutes. In this project, you will investigate the performance of new imaging algorithms for making high-fidelity images of moving and evolving jets.

Research Field Very Long Baseline Interferometry


Project Supervisor Associate Professor James Miller-Jones [email protected] Co-Supervisors

45

Resolving Pico-arcsecond Structures in Relativistic Plasmas Around Pulsars

Pulsars, or neutron stars, are exquisite laboratories for studying extreme, high-energy physics. Their super strong gravitational and magnetic fields cannot be replicated on Earth, making the environments of pulsars the only places in the Universe in which ultra-relativistic plasmas can be studied. Pulsars emit highly coherent beams of radio waves, which are detected as a series of pulses as the neutron stars rotate and the beams sweep by the Earth. The physics that underlie the emission mechanism is not well understood and is one of the most celebrated unsolved problems in modern astrophysics.

Because neutron stars are so small (~25 km in diameter) and distant (thousands of light years), they cannot be resolved by conventional imaging techniques. However, thanks to their rotation, pulse-to-pulse variations in the observed time series contain information about the spatial structure and dynamics of the emitting relativistic plasma. Pulsar signals are known to exhibit structure on a wide range of timescales, from milliseconds and microseconds down to nanoseconds (cf. Hankins 1971, Cordes 1981, Hankins et al. 2003), with the finest time structures corresponding to physical structures on the order of metres!

Owing to the technical challenges of obtaining high-quality, ultra-high-time resolution recordings of pulsars, the smallest timescales (~microseconds to nanoseconds) are rarely studied in detail. However, recent advances in instrumentation and software have now made this possible with the Murchison Widefield Array (MWA), Australia's premier pathfinder telescope for the Square Kilometer Array (SKA) project. As a well-established instrument for pulsar studies, the MWA is uniquely positioned to become a leader in ultra-high time resolution studies of pulsar emission mechanism.

This project will exploit the MWA's new high-time resolution capabilities to study several bright pulsars in the southern sky, whose micropulses (i.e. microsecond structures) have not previously been observed. The primary focus will be to uncover the physics that governs the dynamics of the relativistic plasma by mapping out the locations of the emitting blobs as they change over time. The frequency structure of “micropulses” will be studied over the full frequency band of the MWA (~ 80 to 300 MHz), yielding further insights into the underlying plasma physics as well as enabling unprecedented studies of the dispersive properties of the interstellar medium through which these micro pulses propagate.

Left: A cartoon diagram showing a pulsar’s polar cap, depicting a carousel arrangement of sparks made up of individual microbursts. Right: A time series showing “nanoshots” in a giant pulse from the Crab pulsar. These structures reveal the presence of emitting regions on the order of metres (from Hankins et al. 2003).

Research Field Pulsar Astrophysics



Co-Supervisors To be advised

46

Search for Terrestrial and Extraterrestrial Technosignatures with the MWA

The radio Search for Extraterrestrial Intelligence (SETI) is a worldwide effort aiming at detecting artificial radio transmissions from intelligent and communicative civilizations throughout the Universe, and demonstrate the non-uniqueness of life across the Universe. Many SETI programs have been conducted over the last decades, searching for narrowband features of non-human origin. Most of these ran on commensally collected data from world-class radio telescopes, with limited flexibility in sky, time, and frequency coverage.

The Murchison Widefield Array is (MWA), operated by the Curtin Institute of Radio Astronomy, is a low-frequency radio interferometer unparalleled in its wide field-of-view and the flexibility it offers to implement state-of-the-art signal processing methods to detect unknown artificial transmissions. The project offered here involves the development of an imaging pipeline - called Cyclone - enhancing active information-bearing radio transmissions through the exploitation of their non-stationary features, to distinguish them from natural astronomical transmissions. Figure 1 shows a comparison between the classic astronomical imaging pipeline and the Cyclone pipeline with a simulated data set featuring a natural astronomical source and an artificial transmission. The detected transmitters will then be classified into terrestrial or non-terrestrial sources after a thorough analysis of their locations and trajectory. This imaging system will be the first high-sensitivity wide-field SETI pipeline, releasing spatial constraints in the search parameter space. The detection of terrestrial transmitters will also support the creation of a Radio Frequency Interference database, providing an accurate assessment of the radio quietness and possible observational threats to the MWA telescope.

This project is suitable for students with Instrumental astronomy / Signal processing / Computer science backgrounds. Good programming skills required (C/CUDA/Python).

a. Simulated result of classic all-sky energy-basedimaging, featuring both an astronomical source (SNR= +5dB, highlighted in red) and an artificialtransmitter (SNR = 0dB, highlighted in green)

b. Simulated result of the Cyclone imaging pipeline ranon the same dataset as shown in figure (a). Thenatural source is this time not detected, whereas theartificial transmission has been enhanced.

Figure 1. Simulated comparison between the classic astronomical imaging pipeline and the Cyclone imaging pipeline



Project Supervisor Dr Ian Morrison [email protected] Co-SupervisorsDr Gregory [email protected]

47

Searching for bound supernova remnants

When a white dwarf explodes in a supernova, it may leave behind a bound remnant that is expelled with a large velocity. Supernovae that involve white dwarfs are classified as Type Ia supernovae. These cataclysmic events are standard candles used to measure cosmological distances and measure the age of the universe. We know that these types of supernovae are caused by the thermonuclear disruption of a white dwarf whose mass has reached the Chandrasekhar limit of 1.4 solar masses, the maximum mass of a white dwarf star. However, we know very little of the evolutionary paths leading to these explosions. A subclass of Type Ia supernovae are the subluminous Type Ia supernovae and these are predicted to leave behind a remnant of the exploding white dwarf. Only a handful of these remnants have been found.

The aim of this project will be to search for bound remnants and to study the properties of these stars. These surviving stars can be identified first by their peculiar Galactic motion and also their unusual physical characteristics, such a very low mass and an atmosphere without hydrogen or helium. As part of this project you will measure the stars’ motion through the Milky Way and retrace its past motion to identify the position of the supernova event. You will also analyse spectroscopic and photometric data to determine the bound remnants’ properties such as the temperature, mass and atmospheric composition using the latest model atmosphere and spectral syntheses codes.

This project will exploit the data from the orbital observatory Gaia that is measuring accurate positions, distances and velocities of over a 100 million stars in the Milky Way. The project will also involve observations obtained using the 4m to 8m optical telescopes of the European Southern Observatory (ESO) that is located in the Chilean Atacama desert and which provides the best observing conditions on Earth. These telescopes are equipped with state-of-the-art instruments covering a vast range of the electromagnetic spectrum from the near ultraviolet and optical to the infrared. Therefore, ESO and Gaia provide the ideal tools that are needed to carry out detailed studies of white dwarf stars, including bound remnants of supernova explosions.

Figure 1: Artistic view of the remnant of a supernova explosion (Copyright Russell Kightley ((http://scientific.pictures), used with permission.

Research Field Stellar astrophysics



Co-Supervisors A/Prof James Miller-Jones

http://scientific.pictures/

48

Searching for evidence of feedback in Centaurus A

Radio galaxies are objects that are highly luminous in the radio band of the electromagnetic spectrum. They are the result of matter being accreted onto the supermassive black hole at the centre of a galaxy, causing long jets of particles and radiation to be fired out into the intergalactic medium. Generally, these objects are at huge distances and very large telescopes are required to resolve their structure. Radio galaxies provide a means for astronomers to indirectly study black holes and it is postulated that they may play an important role in the evolution of galaxies and hence the structure of the Universe.

The closest radio galaxy to Earth by a long margin is known as Centaurus A (pictured right). Its close proximity means that it covers a large angular extent across the sky (from top to bottom it is about 7 degrees across, that’s 14 full-Moon diameters!). Hence it can be studied in great detail, making it a unique local laboratory for astronomers to explore supermassive black holes and their interactions with the surrounding environment.

The Murchison Widefield Array (MWA) telescope is an interferometer consisting of 256 antenna tiles, tuned to low radio frequencies (including both the FM radio and digital TV bands) and situated in the West Australian outback. Due to its wide field of view, it is ideally suited to studying Centaurus A.

This project will use new images from the MWA, combined with multi-wavelength data from X-ray and other telescopes, to study how the jets interact with the environment in the northern lobe of the radio galaxy, and to see if this has affected the evolution of the galaxy in a process known as Active Galactic Nuclei (AGN) feedback.




Co-Supervisors Prof. Melanie Johnston-Hollitt [email protected]

Our closest neighbouring radio galaxy Centaurus A as imaged by the MWA telescope at 150 MHz.

49

Searching for Fast Radio Burst counterparts with the Transiting Exoplanet Survey Satellite (TESS)

Fast Radio Bursts (FRBs) are very short timescale and powerful bursts of radio emission that originate from distant galaxies. Thousands occur per day, but they occur randomly on the sky. Therefore, very wide field and sensitive radio telescopes are required to detect them and localise the radio emission to a particular galaxy. The CIRA FRB group is leading the world in this research, using the ASKAP radio telescope. The project offered here is motivated by the need to localise FRBs and, in a stretch goal, examine their emission at wavelengths other than radio. This represents a huge challenge in that one requires a second telescope to observe the same patch of sky at the same time as a radio telescope doing an FRB search when it finds an FRB. This very rarely happens. However, the Transiting Exoplanet Survey Satellite (TESS), which is designed to detect exoplanet eclipses, has optical cameras that cover a very large fraction of the celestial sphere. This means that when radio telescopes detect FRBs, there is a reasonable chance that TESS was looking in the right direction at the right time. In this project, we will utilise the ensemble of historical FRB detections and TESS data to search for the simultaneous optical counterparts for FRBs, aiming to put the very first constraints on simultaneous optical and radio emission from FRBs and perhaps localising previously unlocalised FRBs, identifying their host galaxies.

Aims of project:

(i) Analyse the historical FRB database and identify FRBs for which simultaneous TESS data exist;

(ii) Obtain TESS data from the archive, process the data, and perform a search for optical emissioncoincident with the FRB (in time and position on the sky);

(iii) Write a short paper with the results for publication in an international journal.

The Transiting Exoplanet Survey Satellite (TESS), whose data will be used for this project.

Research Field Radio Astronomy Project Suitability Honours or 3rd Year project or short term intern or vacation student Project Supervisor Prof. Steven Tingay [email protected]

Co-Supervisors

50

Searching for merged stars in the white dwarf population

White dwarfs that underwent a merger event will have distinctive properties. The most notable of these are the acquisition of a magnetic field and fast rotation. One group of white dwarfs, the rare hot, carbon-rich white dwarfs (hot DQs), has an exceptionally high incidence of magnetism and fast rotation as compared to the general white dwarf population. These stars with their unusual atmospheric composition are also more massive than average white dwarfs, and all these properties suggest that they are products of merger events. Currently, only a small number of these stars are known, and they all have similarly hot effective temperatures. We do not know what their descendants are. Since white dwarfs are no longer burning any fuel, they are simply radiating out their internal heat and therefore they become cooler with age. Descendants of hot DQ stars will therefore have similar properties to hot DQs but will be much cooler.

The aim of this project will be to identify candidate white dwarfs that have carbon in their atmosphere but have lower temperatures. Such white dwarfs exist, but their properties such as mass and rotation are largely unknown and therefore, they cannot be evolutionarily linked to hot DQs. As part of this project you will analyse spectroscopic, spectropolarimetric and photometric data of these candidate descendants and determine their stellar properties such as their temperature, mass and atmospheric composition using the latest model atmosphere and spectral syntheses codes.

The European Southern Observatory (ESO) operates several 4m to 8m optical telescopes in the Chilean Atacama Desert which provides the best observing conditions on Earth. These telescopes are equipped with state-of-the-art instruments covering a vast range of the electromagnetic spectrum from the near ultraviolet and optical to the infrared. This project will also exploit data from the orbital observatory Gaia that is measuring accurate positions, distances and velocities of over 100 million stars in the Milky Way. Therefore, ESO and Gaia will provide the ideal tools to carry out detailed studies of these hot DQs and their descendants.

Figure 1: A spectrum of a carbon-rich white dwarf showing Zeeman broadened carbon lines representative of a magnetic field of 0.6 MG (top) and a circular polarization spectrum showing the characteristic choppy pattern of the Zeeman components of the carbon lines (bottom).





Searching for optical transients with the Desert Fireball Network.

The Desert Fireball Network (DFN, fireballsinthesky.com.au) is a project that aims to detect bright meteors (fireballs) as they fall through the sky, and to retrieve the meteorites that they may drop. The DFN group have deployed cameras all over the southern and western parts of Australia as part of their work. As part of a collaboration between the Murchison Widefield Array (MWA) and the DFN group, a camera has been installed near Wooleen station that is part of the DFN network, but is specially built for astronomy observations. We call this the astrocam!

The astrocam has a very wide field of view (100x80°), can detect stars as faint as 10th magnitude, and has a fully automatic observing schedule. We have developed a calibration method that will allow us to extract science quality images from the astrocam data. We are now in the nice position of having a large amount of excellent data that needs to be mined for science results.

Research Field

Transients and Variability

Project Suitability

Honours or PhD

Project Supervisor

Dr Paul Hancock, [email protected]

The first part of the project is to use the astrocam images to produce light curves for all the known variable stars above 10th magnitude. With the all-night, all-year observations, and generally favorable weather conditions, this will be the most detailed and largest study of its kind.

The second part of the project is to search for variable stars and transient events that are yet unknown. This includes searching for transient events such: cataclysmic variables, novae, and supernovae. With a sensitivity limit of approx 10th magnitude it will also be possible to find new variable stars, which have gone unnoticed by the more sensitive but narrow surveys carried out on large telescopes.

In this project you will learn about the life cycle of stars. You will also gain experience handling large amounts of data in an automated way and will have access to supercomputing facilities such as Pawsey.

Left: The astrocam that has collected all the data for this project. It is co-located with a normal DFN camera. Right: The constellation of Orion as seen by the astrocam.

51

52

Searching for Primordial Black Holes as Dark Matter

Free floating intermediate mass black holes (many tens of solar masses) are prime candidates for the unknown `dark matter’ which makes up most of the mass of the Universe. They are cold (slow-moving) and would be very hard to spot in the halo of our galaxy. One method to detect them would be via gravitational lensing of distance extra-galactic sources when they pass close to their line of sight. These events would be rare but distinguished by their symmetric variability over time as the black hole reaches and then passes its closest separation to the background source. They would also affect all frequencies equally as lensing does not depend on frequency unlike most intrinsic variability. The Murchison Widefield Array telescope provides us with a great opportunity to discover these symmetrically achromatic variable (SAV) events due to its wide field of view, regular observations of calibrator sources and wide frequency coverage.

The aims of project this project are:

(i) produce images of all archive observations around calibrator sources and search for any transientsources,

(ii) select SAV events, model them, and estimate implications for dark matter,

(iii) follow-up on-going SAV events with high resolution radio, millimetre and optical observations toobserve the distortion of the background source and estimate mass of lensing source,

(iv) use this large data set to provide an archive of calibration solutions and assess the health of thearray over time.

This project will provide novel constraints (or determination) on the nature of dark matter and by providing an archive of calibration solutions it will be of great benefit to the wider astronomical community using MWA data.

Fig 1. Examples of SAV events from Vedantham et al. (2017) potentially caused by free floating black holes in the halo of the Milky Way.




Co-Supervisors Dr Jess Broderick Dr Marcin Sokolowski

http://adsabs.harvard.edu/abs/2017ApJ...845...89V



53

Searching for the First Black Holes with the MWA

How did the first super-massive black holes form and grow? There is growing evidence that some of the very first black holes formed very early in the Universe (within the first billion after the Big Bang) and may have been active during the Epoch of Reionisation when all the neutral hydrogen was reionised. How they grew so big, in such a short period, is not yet understood. During active phases, accreting black holes are the most luminous objects in the Universe often producing powerful jets of out-flowing material. These jets produce synchrotron radiation visible at radio wavelengths which far out-shine the host galaxy. Hence, radio surveys are a key tool in finding super-massive black holes in the early Universe.

This project will comprise three parts:

(i) Studying the broadband radio properties of known powerfulblack holes at high redshift in order tocharacterise their typical jet emission and to examine the role of jets in their evolution. This will involveobserving, reducing and modelling radio data from the Australian Telescope Compact Array.

(ii) Using the all-sky radio surveys from the low-frequency Murchison Widefield Array (MWA: 70-300MHz) and the Australian Square Kilometre Array Pathfinder (ASKAP: 700-1800MHz to search forthe earliest black holes. This part of the project will involve combining data from these two radiotelescopes to select candidate sources in the early Universe.

(iii) Follow-up of candidate early black holes with powerful optical and infrared telescopes such as theVery Large Telescope and the Atacama Large Millimetre Array. Such observations shall be used toweigh the primordial black hole, study its host galaxy and environment.

This project will uniquely exploit the large area surveys from the complementary MWA and ASKAP and pave the way for future studies with the Square Kilometre Array.

Fig 1: Model of the distortion of an accretion disk by a black hole as used in the film Interstellar (James et al. 2015).




Co-Supervisors Dr Jess Broderick Dr Guillaume Drouart

https://en.wikipedia.org/wiki/Reionization

http://www.narrabri.atnf.csiro.au/


https://www.atnf.csiro.au/projects/askap/index.html

http://iopscience.iop.org/article/10.1088/0264-9381/32/6/065001/meta


54

Searching for the origin of magnetic fields in white dwarf stars

The majority of stars end their life as a white dwarf. These stellar remnants are burned out cores which are slowly releasing their internal heat. Due to their high gravity, the majority of stars have atmospheres that are hydrogen-rich or helium-rich. White dwarf atmospheres are open to direct investigations and show the effect of a unique range of physical phenomena. One of these is the presence of magnetic fields in a significant fraction of white dwarfs. The presence of a magnetic field is revealed by Zeeman splitted spectral lines. The origin of these magnetic fields remains an open question, although several theories have been proposed. The merger of two stars is the preferred origin based on current observations. One of these is that magnetic fields are observed more frequently in some spectral types compared to others. The European Southern Observatory (ESO) has been obtaining spectra for several decades and has amassed a large archive of data. You will extract spectra from the ESO archive with the aim of searching for magnetic fields and analyse them to determine their atmospheric parameters and measure their magnetic field strength. You will also explore any connection between the incidence and strength of magnetic fields and other white dwarf properties.


Project Suitability Honours 3rd Year



55

Shedding further light on a cosmic manatee at low radio frequencies

SS433 is a famous Galactic 'microquasar' located at a distance of 18 000 light years from Earth. Through accretion from a companion star onto a compact object - likely a stellar-mass black hole - a pair of relativistic jets are thought to have inflated 'ear-like' structures in the associated surrounding supernova remnant, W50. The resulting distinct shape of W50 has seen it referred to in the past as the 'Manatee Nebula'.

The SS433-W50 system was, until recently, relatively poorly explored at the lowest radio frequencies (i.e. below 250 MHz). In Broderick et al. 2018 (MNRAS, 475, 5360), we presented the deepest map of SS433-W50 made thus far at these frequencies. We used averaged 115-190 MHz data from LOFAR, the Low-Frequency Array, a pan-European radio telescope with its core located in the Netherlands. In our image, shown below, we clearly detected (i) the point-like source SS433 at the centre of the nebula, (ii) the rich structure of W50, including numerous arcs and filaments, and (iii) further extended emission from the nearby Galactic plane, as seen along the right-hand side of the map.

Microquasars evolve on time-scales much faster than their active galactic nuclei (AGN) cousins, hence being excellent laboratories for studying accretion, relativistic jet formation, and the subsequent influence on the ambient environment. In this project, you will recalibrate the 115-190 MHz SS433-W50 LOFAR dataset using the latest standard techniques, as well as additional LOFAR data at an even lower frequency of 60 MHz. By being able to use the full broadband information in the data, and venturing into virtually uncharted parameter space at the very lowest frequencies, you will enable new and important insights into the low-frequency radio spectra of both SS433 and W50, particularly the associated absorption processes thought to be at work (e.g. foreground free-free absorption from ionised gas along the line of sight). You will also investigate the variability of SS433 at low frequencies, and whether the predicted flux densities match well with those extrapolated from much higher-frequency data. This in turn will provide vital information to enable broadband modelling of the synchrotron-emitting plasmons produced when the microquasar begins to flare.

This project will uniquely exploit the frequency coverage of LOFAR, and potentially make use of available Murchison Widefield Array (MWA) data as well. It would be particularly suitable for those students with an interest in the technical aspects of interferometry and radio data analysis. Some programming experience, for example in shell scripting and Python, is useful but not essential.



Project Supervisor Dr Jess [email protected] Co-Supervisors Dr Gemma Anderson


56

“The A-Team”: Low-frequency Observations of the Brightest Radio Galaxies in the Southern Sky

Murchison Widefield Array (MWA) is a low frequency (80 — 300 MHz) radio telescope operating in Western Australia; its location in the southern hemisphere gives it an excellent view of the Galactic Plane, and several bright radio galaxies: Hercules A, Fornax A, Virgo A, Hydra A, Centaurus A, and Pictor A: colloquially and collectively called “The A-Team”.

These radio galaxies are some of the closest and brightest objects visible with the telescope, but are so bright that they are often removed or “peeled” from observations without being well-characterised, in order to reveal fainter sources. However, these objects are interesting, because they are powerful, bright, and close enough that even with the MWA, relatively fine details can be observed. At low frequencies, this can give insights into the nature of the jets emitting from the central black hole; for instance, it is suspected that the jets of Pictor A become partially synchrotron self-absorbed, causing the spectrum to flatten at low frequencies.

This project aims to use the best observations from many hundreds of hours of observations of these very bright sources to completely characterise them over the entire MWA band, as well as new high-resolution observations from the extended MWA and the GMRT to explore their complex morphologies at low frequencies. The resulting sky models will be extremely useful for calibration and peeling for the rest of the international MWA team, and also for future work with the Square Kilometre Array. Insights into the astrophysics of the individual sources may well result in papers in refereed journals.

This project is suited to a student with a strong grounding in astrophysics and a will to learn various software data reduction packages in order to create the best images possible.

Fig 1: Fornax A, as seen in radio “colours” via the GLEAM survey; red = 72 — 103 MHz; green = 103 — 134 MHz; blue= 139 — 170MHz; the lobes have a different spectral behaviour to the central core.



Project Supervisor Dr Natasha [email protected] Co-Supervisors Dr Benjamin McKinley

57

Silicon monoxide masers towards evolved stars

Asymptotic giant branch stars and red super-giant stars are common sources to power silicon monoxide (SiO) masers. Masers can be thought of as naturally-occurring radio-wavelength lasers, and are powered by energetic and exotic conditions in space. In this study, the SiO masers are powered by in-falling and out-flowing motions of gas surrounding an evolved star, most of which are called hydroxyl (OH) or infrared (IR) stars.

As not much is known about these masers, this project presents an opportunity to advance the "big picture" science of evolved stars. The student will process and analyse data collected with the Australia Telescope Compact Array, a radio telescope in northern New South Wales, with approximately 60 targets. Each of the target observations contains multiple spectral line transitions, including each of the v=1, 2 and 3 maser line transitions; any discovery of relationships between the different spectral lines will be an important contribution to the understanding of evolved OH/IR stars

In extremely rare cases, SiO masers can be excited by star-forming regions. A detection of this kind would be very important and have a high impact in the community, warranting further investigations.

In the course of this work, the student will develop a good understanding of interferometry and data processing. The results from this work could easily be formatted into a publication, which would be of huge benefit to a student pursuing research into the future with a PhD or masters project. The project is suitable as either a third year or an honours project.

Aims of project

(i) Identify maser locations in high-resolution data;

(ii) Associate maser parameters with physical conditions;

(iii) Constrain the physical conditions required to exhibit different types of masing conditions, and identify the properties of the v=3 maser line.

Figure: A three-colour image of different infrared maps overlaid with the locations of detected SiO masers. All masers appear to be associated with an OH/IR star. The data associated with this project are high-resolution follow-up observations of each of these locations to learn more of these environments.



Project Supervisor Dr Christopher Jordan [email protected] Co-Supervisors Dr Rajan Chhetri

58

The abundance patterns of metal poor stars in the Milky Way

One of the main challenges in astrophysics is to detect the first stars formed in the Universe. The ideal candidates are old stars that are usually identified by their low metal content in the absence of reliable age measurements. Metals (elements heavier than helium) are produced in the final stages of the life of a stars, and are expunged in supernovae explosion at the death of stars, and therefore significant metal enrichment in the Universe requires multiple cycles of star formation. Since the pristine gas in early Universe lacked metals, therefore lower the metal content of a star, older it would be. Furthermore, the metal poor stars carry chemical imprints of processes that occurred in early galaxies, and thus also provide a window to the mechanism of formation of galaxies.

The catalogues of metal poor stars have expanded enormously, with a few stars that were known in 80s to thousands that are known today. Even more are going to be detected by powerful surveys such as the GALAH, SkyMapper and GAIA. With the advent of the data, statistical study of abundance patterns of metal poor stars has been made possible.

The project would aim to compile sets of metal poor stars from known catalogues, and then to do a statistical study of their chemical abundances. A particular emphasis will be to identify peculiar trends that do know follow the expectations from standard chemical evolution models. And then further: (i) explore the origins of peculiar trends (ii) develop chemical tags to constrain the ages and spatial locations of stars in the Milky Way

For example, one intriguing trend is the relatively high amount of carbon found in a group of metal poor (iron poor) stars (see the black, blue and red points in the figure underneath). The origin of these unusual carbon enhanced stars is an active area of investigation. Many more interesting chemical patterns can be recovered from the existing and upcoming data, and the origin of those trends need to be investigated both with statistical and modelling techniques.

Metal poor stars in the Milky Way: image created from the SAGA database

(Suda et.al. 2008)

Research Field Galactic Archaeology/First stars

Project Suitability Third year, Honours Masters

Project Supervisor Dr Mahavir Sharma [email protected]

Co-Supervisors A/Prof Cathryn Trott [email protected]

59

The environments of the most distant radio galaxies

Understanding galaxy formation and evolution across cosmic time is a fundamental topic in astrophysics, and key science driver for the forthcoming Square Kilometre Array (SKA). In the early Universe, high-redshift radio galaxies (HzRGs; e.g. review by Miley & De Breuck 2008, A&AR, 15, 67) are crucial beacons for investigating how the most massive galaxies form (e.g. left panel below), and their link to the massive 'red and dead' ellipticals that are the brightest cluster galaxies in the more local Universe.

HzRGs are rare. An efficient way of finding these objects is to select samples of sources with ultra-steep (USS) radio spectra, i.e. where the source flux density decreases rapidly withincreasing frequency. Using lower-frequency catalogues withdeep detection limits is therefore expected to be advantageous,and indeed has recently led to the discovery of the most distantradio galaxy currently known (right panel below).

In this project, you will use data from the Murchison Widefield Array (MWA), the Australian SKA Pathfinder (ASKAP), and the Australia Telescope Compact Array (ATCA), as well as additional multi-wavelength data from other facilities, to find and subsequently investigate new HzRG candidates. This project will address, but is not limited to, topics such as the following:

(i) Can the deepest MWA observations uncover a significant number of previously unknown distantradio galaxies?(ii) What is the underlying reason for the success of the USS selection method? The superb broadbandcoverage of the MWA, ASKAP and the ATCA will enable new important insights.(iii) What are the typical environments in which the most distant galaxies reside, and how is this reflectedin their properties (particularly their radio polarimetric properties, such as polarisation fraction andFaraday rotation measure)?(iv) Given a multi-wavelength dataset, what does a HzRG typically look like? Moreover, how can wemost efficiently select HzRG candidates in the era of the SKA, where catalogues will comprise billionsof sources?

Left: The 'spiderweb galaxy' at redshift z = 2.2: witnessing the formation of a dominant cluster galaxy in the early Universe. The greyscale is a Hubble Space telescope image, while Lyα (blue) and radio contours (red) are also shown. Figure from Miley et al. 2006 (ApJ, 650, L29). Right: Radio contours overlaid on a near-infrared K-band image of the most distant radio galaxy currently known, TGSS J1530+1049 at a redshift z = 5.72 (i.e. when the Universe was only 1 billion years old). Figure from Saxena et al. 2018 (MNRAS, 480, 2733).



Project Supervisor Dr Jess Broderick [email protected]

Co-Supervisors Dr Nick Seymour


60

The Evolution of Black Holes Across Cosmic Time

The formation and evolution of the super-massive black holes which reside in the centres of most galaxies remains one of the principle mysteries of astrophysics. We know that they evolve via two processes: merging (along with their host galaxies) and accretion. Their merging history would have to be consistent with models and observations of galaxy evolution, as well as future gravitational wave results (e.g. from LISA). Their accretion history can be constrained by X-ray and mid-IR surveys (for high accretion rates) and by radio surveys probing the relativistic jets emitted at low accretions rates. Hence it is possible to determine how the distribution of black holes masses evolves from the present day to the early Universe.

This project aims to:

(i) develop models to relate accretion rates and states of the accretion disk with observables such asX-ray, mid-IR and radio surveys. In particular, this work would focus on using multi-frequency radiosurveys (e.g. the Murchison Widefield Array) to constrain the power of radio jets and therefore theaccretion related to the radio emission. This work would also build upon our knowledge of galactic blackholes,

(ii) use these models to determine the backward evolution of the black hole mass function consistentwith observables,

(iii) examine the processes which could lead to the rapid formation of black holes in the early Universeand the effect they have on their environment,

(iv) make predictions of observables from accreting black holes at high redshift taking into accountfactors such as inverse Compton scattering of the CMB by relativistic electrons from the radio jets.

This project will uniquely exploit the broad frequency coverage of many Australian radio telescopes such to constraint the evolution of super-massive black holes across cosmic time.

Fig 1: Model of the distoration of an accretion disk by a black hole as used in the film Interstella (James et al. 2015).




Co-Supervisors Dr Jess Broderick

https://lisa.nasa.gov/




61

The explosive outbursts of black holes

The release of gravitational potential energy as matter falls onto a compact object such as a black hole powers the most energetic phenomena in the Universe, allowing us to study higher energies and stronger gravitational fields than could ever be reproduced in a laboratory here on Earth.

As matter falls onto a black hole, its angular momentum causes it to form a rotating accretion disc around the central object. However, matter does not only flow inwards. Some fraction of the infalling material can be diverted outwards in relativistically-moving, oppositely directed, bipolar jets, or in slower, more massive, equatorial winds. Different geometries of the inflowing gas appear to be associated with these different types of outflow. With multiwavelength observations, we can probe all these different components of the system; jets, winds and accretion flow. On occasion, the accretion rate onto the central black hole increases by several orders of magnitude, changing both the inflow geometry and the nature of the outflows, and causing a dramatic increase in the amount of light emitted at all wavelengths.

We believe that the same physics governs the behaviour of these stellar-mass compact objects as governs their more massive analogues in the supermassive black holes seen at the centres of galaxies (Active Galactic Nuclei; AGN). However, since stellar-mass objects evolve on much faster timescales (days and weeks rather than millennia), they act as unique probes of the physics governing the accretion and outflow around black holes. We can study the explosive outbursts of these systems as they evolve in real time, providing new insights into their radiative and kinetic feedback that has an impact on cosmological scales

In this project, you will work as part of a large international team conducting multi-wavelength observational studies of the explosive outbursts of black hole X-ray binary systems, aiming to understand how these powerful events evolve, and in particular the connection between the changing conditions in the inflow and the launching of relativistic jets.

Left: A schematic of a black hole accreting matter from a donor star via an accretion disk. Relativistic jets (shown in red and purple, as observed in right panel) are launched from the inner regions of the accretion flow.

Research Field Accretion Physics

Project Suitability PhD Project Supervisor Associate Professor [email protected] Co-Supervisors Dr Arash Bahramian

62

The Impact of Proto-clusters on Radio Galaxies

Clusters of galaxies are the most massive bound structures inthe Universe lying at the crossroads of the large-scale structure.In the nearby Universe they are dominated by massivegalaxies with very low star formation rates, but in past they musthave been forming stars at a prodigious rate. However, findingyoung proto-clusters in the distant Universe is difficult as typicalsearch methods (e.g. X-ray surveys, Sunyaev-Zel'dovich effect) become much less sensitive. High redshiftradio galaxies are known to lie in over-dense, proto-cluster environments and to be beacons regions of extreme star formation. This is due to the radio galaxy being powered by a massive and rapidly growing black hole. Scaling relations then suggest that this black hole will be in the most massive dark matter halo. This project will take advantage of low-frequency radio surveys with the Murchison Widefield Array (MWA) and a plethora of other higher frequency radio data (from ATCA to ALMA) to study how the radio galaxy impacts the cluster and how the cluster impacts the radio galaxy.

This project will comprise three parts:

(i) Compiling and modelling high to low radio frequency observations to measure the powersand ages of the radio jets.

(ii) Modelling the expected X-ray emission from the radio galaxy due to the interaction ofreletivitic electrons in the jet with the Cosmic Microwave Background via Inverse Comptonlosses. These predictions can be compared with X-ray emission from eROSITA.

(iii) Using high and low resolution radio images to search for evidence of Sunyaev-Zel’dovicheffect in proto-clusters at high redshift. Such results will provide the first direct measure ofthe total mass (including dark matter) of these proto-clusters.

Fig 1: The Spiderweb Galaxy. Deep Hubble image of the core of the MRC 1138-262 protocluster at z = 2.2 obtained with the Advanced Camera for Surveys.(Miley et al., 2006). Superimposed on the HST image are contours of Lyα (blue) obtained with ESO's very Large Telescope (VLT), delineating the gaseous nebula and radio 8GHz contours (red) obtained with NRAO's VLA, delineating the non-thermal radio emission.

Research FieldRadio Astronomy Project SuitabilityPhD Honours

Project SupervisorDr Nick [email protected] Co-Supervisors Dr Guillaume Drouart


The ionization bubbles in the early Universe

After the beginning in the big bang, the Universe cooled as it expanded. At a redshift of approximately 1100, the hydrogen recombined and cosmic microwave background (CMB) photons were emitted. Thereafter, the Universe became neutral and dark, as it entered into the so called `Dark Ages’, that continued up until a redshift of about 20, when the first stars and galaxies came into existence. These first sources produced ionizing photons that (re-)ionized the surrounding neutral hydrogen. The ionized regions thus created, also known as HII bubbles keep on expanding with time as they eat through (ionize) the neutral hydrogen in the Universe. The neutral hydrogen, however, has a characteristic signal at very low frequencies that is known as the 21 cm spin-flip (hyperfine) line. By detecting this redshifted line provides a probe of the sizes of diminishing neutral hydrogen islands (and conversely that of the sizes of expanding HII bubbles).

The Square Kilometer Array (SKA) will measure the 21 cm signal precisely. The ionized HII bubbles created by stellar populations in first galaxies expand as they are fuelled by ionizing photons generated during the lifetime of stars, and the dynamics of their expansion can be worked out with radiative transfer equations. It is of paramount importance to know whether an expanding HII bubble will break out of the galaxy or not. However, the brute force method that envisages detailed radiative transfer calculation for every galaxy in a simulation running at cosmological scales is computationally not feasible.

The idea is to develop remedies to bypass the brute force approach, and this project therefore will undertake the modelling of HII bubbles in galaxies. The stars act as sources and the already ionized gas has a tendency to recombine that acts as sink. The aim is to derive an efficacy factor, that is, how many photons per H atom are needed to ionize a galaxy. The project can be extended to investigate the implications for 21 cm power spectrum which is one of the main objectives of major radio telescopes (MWA, SKA). A parallel study will be carried out to investigate the variation in efficacy factor for bubbles expanding in different hydrostatic density profiles.

The Epoch of Reionization and early HII bubbles: image taken

from Loeb 2006

Research Field Cosmic reionization/gas dynamics


Project Supervisor Dr Mahavir Sharma [email protected]

Co-Supervisors A/Prof Cathryn Trott [email protected]

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The time domain radio sky from SKA-Low prototypes

SKA-Low prototype systems AAVS1 and EDA2 have been surveying the low frequency radio sky since 2017. These radio telescopes see the entire sky with a time resolution of a few seconds. This project will process archival data to search for transient and variable radio sources, taking advantage of the all-sky field-of-view of the telescopes.

The SKA-Low prototype systems AAVS1 and EDA2 consist of 256 antenna “dipoles” pseudo-randomly arranged in an area 35 metres in diameter.

Aims of project

(i) re-process data from AAVS1/EDA2 with a focus on time-domain imaging and source detection

(ii) identification of sources of transient/variable radio emission

(iii) working towards building a pseudo real-time imaging systemfor EDA2 data

This project exploits the opportunity for end-to-end data processing for an SKA-Low prototype system, enabled by the combination of engineering and science-focussed activities for SKA at CIRA.

Figure 1: An example all-sky image generated by the SKA-Low prototype system AAVS1.

Figure 2: The Engineering Development Array (EDA) prototype system for SKA-Low


Project Suitability

Honours (as appropriate)

Project Supervisor A/Prof Randall Wayth [email protected]

Co-Supervisors

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Towards more realistic MWA simulations using OSKAR

The Murchison Widefield Array (MWA) is a low frequency radio (think FM radio waves) interferometer consisting of 2048 dipole antennas, spread over 5km out in the WA outback. The MWA is indirectly capable of imaging the radio sky by correlating and processing the signals captured by each antenna, rather than immediately making an image like a traditional optical telescope. The data collected by the telescope is affected by a slew of instrumental effects such as receiver noise, reflections within cables connecting antennas, and frequency related effects imparted by the analogue signal processing known as the ‘bandpass’. All these effects must be understood and mitigated to enable science.

Real data contains unknown astrophysical and atmospheric effects as well as these instrumental effects, making it hard to isolate and understand each effect. Realistically simulating observations gives us a path to individually investigate each effect and test our calibration and imaging software. Simulating interferometric data is computationally expensive, and as such requires efficient code. OSKAR is such a simulation package and utilises GPU acceleration to simulate up to millions of radio sources. In the images below, a real observation is shown on the left, and an OSKAR simulation shown on the right, showing excellent agreement.

Figure – Left: 2 minutes of real MWA data imaged. Each bright spot is an image of a radio-emitting galaxy. Right: 2 minutes of MWA data simulated using OSKAR and 300,000 radio sources

OSKAR is a generic package and as such does not include the instrumental quirks of the MWA. The aims of this project then would be:

• Add instrumental effects, such as the bandpass and cable reflections into the OSKARsimulation pipeline. This could either be done internally to the OSKAR code or added to thedata after the fact, depending on the computational experience of the student

• Test how well our current calibration software, the RTS, deals with these instrumental effects,and investigate how this might affect the scientific quality of processed MWA data

• Compare to real data from the MWA• Depending on the scope of the project, think about adding atmospheric effects from the

ionosphere into the OSKAR simulation package

Research Field Radio Astronomy/Computer Engineering

Project Suitability Masters PhD

Project Supervisor Dr Jack Line [email protected]

Co-Supervisors A. Prof Cathryn [email protected]

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Uncovering Southern-sky Pulsars with a Next-generation Low-frequency Radio Telescope

Pulsars – rapidly-rotating, highly-magnetized neutron stars that emit beams of radiation like cosmic light houses – are nature’s premier laboratories for advancing fundamental physics. With applications ranging from testing strong-field gravity to probing the state of ultra-dense matter, they enable us to push the boundaries of physics. While > 2500 pulsars are currently known, a vast majority were found in surveys using large single-dish telescopes such as the Parkes and Green Bank telescopes. Historically, pulsar surveys are proven to be highly rewarding, with a multitude of science enabled by the discoveries of exotic objects and specialised targets, including pulsars in relativistic binary systems, millisecond pulsars, and those with extreme magnetic fields. Not surprisingly, fundamental physics with pulsars is a headline science theme for the Square Kilometre Array (SKA), and conducting a full cosmic census of the Galactic pulsar population is a high-profile key science driver for the SKA.

However, finding pulsars with the SKA precursor and pathfinder telescopes pose numerous challenges. The computational costs involved in beamforming and signal processing are prohibitive, besides the inherent complexity in realising the full potential given their large field of view and attainable survey efficiency. Australia’s Murchison Widefield Array (MWA) – a low-frequency (80-300 MHz) telescope in Western Australia, and an official precursor for the low-frequency SKA – is no exception. Fortunately, with a major recent upgrade (i.e. the Phase 2 MWA), it has become possible to conduct sensitive pulsar searches with the MWA, reaching a survey efficiency ~2-3 orders magnitude higher than that possible with any other currently operational facilities around the world.

This project will involve processing large volumes of (~Petabyte scale) high time resolution data from an all-sky pulsar survey under way at the MWA – the Southern-sky MWA Rapid Two-metre (SMART) pulsar survey. It is an ambitious program to search the vast southern skies with a high sensitivity at low radio frequencies. The survey is expected to discover hundreds of pulsars including dozens of millisecond pulsars (Figure 1), and will serve an important reference for future surveys planned with the upcoming SKA. The MWA’s unique access to the southern sky means exploring a new parameter space, and thence potential for making exciting discoveries, and prospects for high impact science.

Figure 1: The pulsar population detectable with the SMART pulsar survey under way at the MWA. The filled circles in grey are long-period pulsars (i.e. spin periods ~ seconds) whereas those in colour represent millisecond pulsars.




Co-Supervisors Dr Ian Morrison George Hobbs (CASS)

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Using the Five hundred metre Aperture Spherical Telescope to detect the highest energy cosmic rays

Cosmic rays are the highest-energy particles in nature, impacting the Earth with energies more than a million times higher than can be achieved with the Large Hadron Collider. Yet we don’t know where they come from. This is because cosmic magnetic fields deflect cosmic ray trajectories during propagation. As cosmic ray energy increases, this deflection may become small enough to trace cosmic rays back to their origin – but the highest-energy particles are very rare, arriving at a rate of one per square kilometre per century.

How to detect enough of these ‘ultra-high’ energy cosmic rays? The ‘lunar technique’ is a method for solving this problem. When a cosmic ray interacts, it gives off a burst of radio-wave radiation, lasting a few nanoseconds. By pointing a ground-based radio-telescope at the Moon, cosmic rays hitting the lunar surface might be detected. And the largest single-dish radio telescope in the world – the Five hundred metre Aperture Spherical Telescope (FAST) - has just been completed in Guizhou Province, China. However, to use FAST to detect lunar signals, the effect of the rough lunar surface on the signal shape needs to be modelled. Solving this problem will be the aim of the project.

Aims of project:

(i) Model the rough lunar surface.

(ii) Apply surface-transmission equations to model radio emission from cosmic ray cascades.

(iii) Determine whether current radio telescopes can observe these signals – and then go anddiscover them!

The results of this investigation will inform not just a planned experiment with FAST, but also proposed lunar missions such as LORD (Russia), and potential ground-based radio observations with the Parkes and Effelsburg telescopes (Australia and Germany, respectively). An honours project would target aims (i) and (ii), while a PhD student may have the opportunity of participating in observations, extending their results to experiments searching for neutrinos underneath the Antarctic ice, and potentially visiting international collaborators such as Prof Jaime Alvarez-Muniz in Spain.

(Right) The Five hundred metre Aperture Spherical Telescope (FAST). This instrument will be used to search for cosmic rays hitting the Moon. (Below) Bootprint of an astronaut on an Apollo mission. Data from these missions will be used to model the lunar surface.

Research Field Particle physics/radio astronomy


Project Supervisor Dr Clancy James [email protected] Co-Supervisors Prof Jaime Alvarez-Muniz, ProfXiang-Ping WuUniversity of Santiago de Compostela, Spain; National Astronomical Observatories, China

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Verification and Measurement of Noise Coupling in a Low-Frequency Radio Telescope

A low-frequency radio telescope operates in the frequency range of tens to hundreds of MHz. Salient examples in the Western Australian context include the Murchison Widefield Array (MWA) which spans the 80-300 MHz bandwidth and the Low-Frequency Square Kilometre Array (SKA-Low) which covers 50 MHz to 350 MHz. In a low-frequency radio telescope, many antennas in an array are situated close to one another. In this environment, the noise generated by the low-noise amplifiers (LNAs) is re-radiated and pick up by all elements in the array which causes a bias in the correlation matrix produced by the telescope.

The potential impact of this effect to radio astronomy observation has been widely recognized. Theories and calculation methods have been published in the literature to account for this. However, verification of the results has generally been lacking. The primary objective of this project is to fill that gap. This particular project seeks to verify the theory by measuring the antennas under test in a controlled environment such as the anechoic chamber (see figure).

Since the noise generated by this environment is constant ambient noise, we expect this to be the ideal condition to verify the noise coupling theory. We will measure the electromagnetic coupling and noise coupling between two antennas connected to the LNAs with known noise parameters. We will then increase the number of elements to as many as the Curtin University anechoic chamber will accommodate. This is expected to be the first explicit verification of noise coupling in the context of antenna arrays.

Research Field Radio Astronomy Engineering

Project Suitability MPhil/ Honours

Project Supervisor Dr Adrian Sutinjo [email protected]

Co-Supervisors Dr. Budi Juswardy Mr. Daniel Ung

post-graduate research projects

Documents

Transcript of post-graduate research projects