# 2020 MWA Virtual Project Meeting

Australia/Perth
Description

Dear all, new dates have been announced for the project meeting, commencing:

0800 July 16th and 17th (AWST, UTC+8)

0000 July 16th and 17th (UTC)

2200 July 15th and 16th (EDT, UTC-4)

View full timetable

Join the virtual meeting

Watch the livestream/recordings

This meeting will encompass topics from the MWA's key science goals (such as transients, galaxies, solar and ionosphere physics, and the EoR), engineering (research and developments towards MWA Phase III) and management (including updates from the operations team and the Murchison site).

The program is envisaged to have sessions across two days, with a greater time allocation for the science sessions. The sessions will be held as Zoom videoconference meetings, which will also be recorded, live-streamed and stored on the MWA's Youtube channel.

There will be a one day MWA Board meeting preceding the project meeting.

Participants
• Alexander Williamson
• Aman Chokshi
• Amanda Wilbert
• Andrew McPhail
• Andrew Williams
• Atsushi Nishizawa
• Bart Pindor
• Benjamin McKinley
• Benjamin Quici
• Brendan Hennessy
• Brian Crosse
• Bryan Gaensler
• Cathie Zheng
• Cathryn Trott
• Charlotte Sobey
• Chenoa Tremblay
• Chenxi Shan
• Christene Lynch
• Christopher Jordan
• Christopher Riseley
• Dan Hu
• Daniel Jacobs
• Daniel Price
• David Emrich
• David Kenney
• Denis Leahy
• Devojyoti Kansabanik
• Dilpreet Kaur
• Divya Oberoi
• George Heald
• Greg Sleap
• Hariharan Krishnan
• Ian Morrison
• Iver Cairns
• Jack Line
• Jake Jones
• Jess Broderick
• John Morgan
• Jonathan Pober
• Judd Bowman
• Jun Tian
• Kamen Kozarev
• Kathryn Ross
• Keitaro Takahashi
• Lindsay Berkhout
• Luke Pratley
• Mahsa Rahimi
• Marcin Sokolowski
• Maria Kovaleva
• Melanie Johnston-Hollitt
• Mengyao Xue
• Mia Walker
• Miguel Morales
• Minfeng Gu
• Natasha Hurley-Walker
• Nicholas Seymour
• Nicholas Swainston
• Nichole Barry
• O. Ivy Wong
• Parul Janagal
• Paul Hancock
• Philippa Patterson
• Phillip Giersch
• Pyxie Star
• Ramesh Bhat
• Randall Wayth
• Ray Norris
• Rike McLernon
• Rohit Sharma
• Ruby Byrne
• Sam McSweeney
• Sarah White
• Shintaro Yoshiura
• Stefan Duchesne
• Steven Murray
• Stuart Wyithe
• Surajit Mondal
• Susmita Sett
• Takuya Akahori
• Tessa Vernstrom
• Torrance Hodgson
• Yang Lu
• Yongjun Chen
• Yvette Perrott
• Zhijun Xu
• Zhongli Zhang
Contact
• Wednesday, July 15
• 8:00 AM 10:00 AM
Management: Board Meeting
• 10:00 AM 10:20 AM
Coffee 20m
• 10:20 AM 12:00 PM
Management: Board Meeting
• 12:00 PM 1:00 PM
Lunch 1h
• 1:00 PM 3:00 PM
Management: Board Meeting
• Thursday, July 16
• 8:00 AM 8:40 AM
Management: Welcome
• 8:00 AM
Welcome by MWA Board Chair 10m
Speaker: Stuart Wyithe
• 8:10 AM
MWA Director's Report 20m
Speaker: Melanie Johnston-Hollitt (ICRAR/Curtin)
• 8:30 AM
Principal Scientist's Update 10m
• 8:40 AM 10:00 AM
Science: EoR
• 8:40 AM
Multi-redshift upper limits on the signal from the Epoch of Reionisation using the Murchison Widefield Array 20m

Detecting and characterising the neutral hydrogen 21cm signal from the first billion years of the Universe remains a primary goal of most low-frequency radio telescopes. The structure and evolution of this signal encodes key information about the formation of structure in the early Universe, in the period termed the Epoch of Reionisation. In this talk, I will describe recent results from the MWA experiment. We compute the spherically-averaged power spectrum from four seasons of data obtained for the Epoch of Reionisation project observed with the MWA. We measure the EoR power spectrum over a range of scales at redshifts z=6.5-8.7. The largest aggregation of 110 hours on the EoR0 field in the high-band yields a lowest measurement of (43~mK)^2 at k=0.14 hMpc^{-1} and z=6.5 (2 sigma thermal noise plus sample variance). Using the Real-Time System to calibrate and the CHIPS pipeline to estimate power spectra, we select the best observations from the 2013-2016 observing seasons, observing three independent fields and in two frequency bands. We choose the cleanest 8,935 observations (298 hours of data) to form integrated power spectra over the different fields, pointings and redshift ranges.

Speaker: Cathryn Trott (ICRAR - Curtin University)
• 9:00 AM
A Unified Calibration Framework for 21 cm Cosmology 20m

Calibration approaches for 21 cm cosmology experiments can be broadly categorized as either ‘sky-based,’ relying on an extremely accurate model of astronomical foreground emission, or ‘redundant,’ requiring a precisely regular array with near-identical antenna response patterns. We show that sky-based and redundant calibration can be unified into a highly general and physically motivated calibration framework based on a Bayesian statistical formalism. This novel calibration framework relaxes the rigid assumptions implicit in each sky-based and redundant calibration. It can account for sky model incompleteness, antenna position offsets, and beam response inhomogeneities. Furthermore, it enables new calibration techniques such as redundant calibration of arrays with no redundant baselines, such as the MWA Phase I. These new techniques could mitigate systematics and reduce calibration error, thereby improving the precision of cosmological measurements.

Speaker: Ruby Byrne (University of Washington)
• 9:20 AM
Measuring MWA Beam Shapes Using Satellites 20m

Understanding the beam shapes of the Murchison Widefield Array(MWA) tiles is particularly important to studies of faint structure such as extragalactic mapping and the Epoch of Reionization (EoR). As teams around the globe improve analysis techniques and their understanding of instrumental effects, the 21cm power spectrum detection of EoR structure is in sight. At this stage, understanding the variations in beam shapes of telescopes such as the MWA, will be crucial. In this study, the beam shapes of 14 MWA tiles are measured, in both polarizations and at multiple pointings, using communication satellites. We aim to understand by how much, and in what way, the MWA beams differ from simulations of ‘ideal’ beam shapes. It is well known that the MWA suffers from polarization leakage, where flux from stokes I leaks into other stokes parameters. This effect is known to be of the order of∼1% at the centre of the beam and∼4% towards the edge of the beam. Our study will reveal the extent of this leakage to a much higher accuracy, which will be beneficial to polarization studies of the ISM and the Ionosphere. We will also demonstrate how other telescopes can implement similar experiments easily, using cheap off-the-shelf equipment.

Speaker: Aman Chokshi (University of Melbourne)
• 9:40 AM
WODEN: An MWA specific GPU simulation code 20m

In this talk I'll introduce WODEN*, an MWA specific simulator capable of simulating point source, Gaussian, and shapelet sky models. The code is designed to run on GPUs, to allow simulations with order > 10$^6$ components to run in good time. The over-arching goal of this code is to propagate a full EoR light cone simulation + foregrounds through to data products that can be ingested by our current EoR pipelines, to test our signal recovery strategies.

I'll overview the current features of WODEN, including utilising existing RTS code to use the FEE MWA primary beam model, and the ERFA library for astrometry. I'll also outline plans for comparing the code to pyuvsim to give confidence in the outputs, and using pyuvdata to create data products.

*(WODEN is not an acronym, its the namesake of the Germanic pagan god)

Speaker: Jack Line (ICRAR Curtin University)
• 10:00 AM 10:20 AM
Coffee 20m
• 10:20 AM 12:00 PM
Science: SHI
• 10:20 AM
SHI Update 20m

The past year has been an eventful one for the SHI Collaboration. Our long term investment in developing the tools and techniques have begun to yield interesting results. The MWA solar group has now established itself globally as one of the leading solar radio physics groups. With dynamic ranges (DR) exceeding 100,000, the MWA solar images now represent the state-of-the-art at metrewaves by a large margin. Using these high DR images, we have demonstrated the ability to detect weak radio emission associated with Coronal Mass Ejections, and model them to estimate the entrained magnetic field. Our detailed studies of the well known type III solar bursts have lead to discovery of novel aspects of these bursts, leading to new insights about these systems. We have made our first forays into polarimetric studies of the solar bursts. We have also developed ways to effectively disentangle the intrinsic variations in emission from the propagation effects, which has remained a challenge. Our work has pushed the flux density of the weakest nonthermal emissions detected three orders of magnitude lower. This promises to have interesting implications for the coronal heating problem, one of our long term science objectives. I will summarise the progress which we have made, touch upon some of the projects in progress and briefly describe our near and short term objectives.

Speaker: Divya Oberoi (National Centre for Radio Astrophysics, Pune India)
• 10:40 AM
The MWA IPS Phase-II Survey 20m

The IPS project is part way through its 2nd year of daily observations in phase-II extended configuration. We have already reduced over 100 observations covering over 3000 square degrees.

In this talk I will discuss the early results from this survey, with revised sensitivity and source count estimates, as well as early astrophysical results, including the possible detection of a new population of compact steep spectrum objects, distinct from peaked-spectrum sources.

Speaker: John Morgan
• 11:00 AM
First radio evidence for impulsive heating of the quiet solar corona 20m

In this talk we will explore the relevance of nanoflare based models for heating the quiet sun corona. Using metrewave data from the Murchison Widefield Array, we present the first successful detection of impulsive emissions down to flux densities of ~1mSFU, about two orders of magnitude weaker than earlier attempts. These impulsive emissions have durations less than about a 1s and are present throughout the quiet solar corona. The median fractional time occupancy of these impulsive emissions at a given region is 5%.The histograms of these impulsive emissions follow a powerlaw distribution and show signs of clustering at small timescales. Our estimate of the energy which must be dumped in the corona to generate these impulsive emissions is consistent with the coronal heating requirements. Additionally, the statistical properties of these impulsive emissions are very similar to those recently determined for magnetic switchbacks by the Parker Solar Probe (PSP). We hope that this work will lead to a renewed interest in relating these weak impulsive emissions to the energy deposited in the corona, the quantity of physical interesting from a coronal heating perspective, and explore their relationship with the magnetic switchbacks observed by the PSP.

Speaker: Surajit Mondal (National Centre for Radio Astrophysics)
• 11:20 AM
Probing fine spatial, temporal and spectral structures of the Sun 20m

The Sun is a vast laboratory of plasma. In solar corona, the plasma rests in the heterogeneous magnetic field networks, which are rooted in the photosphere. Besides, solar plasma in corona is also dynamic, which is most drastically seen during a solar flare. Overall, solar emission is inherently variable in space and time. The MWA solar observations have captured this variability and produced most detailed solar maps at meter wavelengths at a fine time cadence. Here, I will present the results from two pieces of work from MWA solar data.

I. At meter wavelengths, coronal propagation effects like scattering and refraction are quite significant and significantly alter the observed brightness distribution of the solar emission. However, these effects have remained hard to quantify. I will present a quantitative comparison of the perceived brightness distribution in the MWA solar maps with simulated thermal bremsstrahlung at corresponding frequencies. We find that the scattering extensively re-distributes the brightness within the solar disk. To give rise to this observed behaviour, coronal density inhomogeneities 1%-5% are required.

II. MWA solar observations have demonstrated the presence of a large population of the energetically-weak releases associated with an active region. Motivated by this, we perform a near-simultaneous study of a gyro-synchrotron (GS) radio source using L-band of VLA and MWA. This source was highly variable, long-lasting and was associated with a complex active region. I will discuss the results from the source modelling and the energy released by such long-term GS sources.

Speaker: Rohit Sharma (University of Applied Sciences Northwestern Switzerland)
• 11:40 AM
Solar flux density calibration with in-field sources for MWA solar observation 20m

Absolute flux density calibration of the Sun is a challenging problem. Due to the very large field of view and high primary beam sidelobes of MWA, the measured flux density of a typical calibrator is significantly contaminated by solar contribution while the Sun is above the horizon. Hence calibrators are observed before sunrise and after sunset, resulting in a significant time separation between the calibrator and source observations. Additionally the Sun is observed using additional attenuation in the signal path, while the calibrators are not.
Absolute flux density calibration is however essential for several solar science goals. Oberoi et al. (2017) developed an innovative non-imaging technique for this. It yields ~10-60% uncertainty in flux density scale and depends on availability of multiple short baseline. The latter restricts its applicability for MWA phase-II extended configuration.
Our autonomous imaging pipeline for solar observations (AIRCARS; Mondal et al. 2019) gives us the ability to make very high dynamic range ($10^3-10^5$) solar images routinely. Recent improvements to this pipeline now allow us to detect several background galactic and extra-galactic sources in the presence of the Sun. We can now also image the large angular scale Galactic plane, with the Sun in the FoV. Taking advantage of this and the availability of catalogue flux densities of these in-field sources, we arrive at the absolute flux density calibration for the Sun. This method has lead to an order of magnitude reduction in the uncertainty on flux density calibration.
These developments also mark the next steps towards our long term science goals of extending the MWA IPS observation time window during the daytime and measuring the CME magnetic field using Faraday rotation of background linear polarized radiation.

Speaker: Devojyoti Kansabanik (National Centre for Radio Astrophysics - Tata Institute of Fundamental Research, Pune, India)
• 12:00 PM 1:00 PM
Lunch 1h
• 1:00 PM 3:20 PM
Science: GEG
• 1:00 PM
GEG Update 20m
Speaker: Chenoa Tremblay
• 1:20 PM
An MWA Phase II follow up of diffuse, non-thermal radio emission in galaxy clusters 20m

The MWA is a low-frequency radio telescope that can probe galaxy clusters on Mega-parsec scales via their non-thermal, diffuse synchrotron emission. Using the Galactic and Extragalactic All-sky MWA (GLEAM) survey (Wayth et al. 2015, Hurley-Walker et al. 2017), we have identified over 500 candidate sources of such emission, increasing from the known ~ 100 examples. These sources, halos and relics, are thought to be formed through shocks and turbulence in the intra-cluster medium, tracing large-scale structure formation and the magnetic fields permeating the clusters. With the upgrade of the MWA to Phase II, the increase in maximum baseline has resulted in almost double the available resolution. We have been leveraging this increase in resolution to re-observe a selection of our original candidates. We will present our data-processing pipeline, the challenges involved with MWA Phase II data processing, the results from our sample to date, and show that the MWA in its extended configuration is able to better determine the nature of these sources.

Speaker: Stefan Duchesne (International Centre for Radio Astronomy Research - Curtin University)
• 1:40 PM

Speaker: Benjamin Quici (Curtin University for Radio Astronomy (CIRA))
• 2:00 PM
Centaurus A like you have never seen it before 20m

The MWA Phase-2 upgrade has effectively doubled the angular resolution of the array, providing an opportunity to examine extended sources in greater detail. Centaurus A, our closest neighbouring radio galaxy and the largest in angular extent on the sky, is particularly challenging to image due to the large range in brightness and spatial scale that it spans. Incomplete uv-coverage has hampered previous efforts to reveal the complex feedback mechanisms that govern the evolution of the radio source as relativistic particles stream from the dense, bright core to form both large and small-scale structures in the faint radio lobes. I will present new MWA images combining data from both phase 1 and phase 2-extended configurations using joint deconvolution, which provide arguably the best view of the entire radio source to date and the ability to gain new insights into the physics at work in the lobes and the transition regions where energy is transferred between small and large scales.

Speaker: Benjamin McKinley
• 2:20 PM
All-sky results from the POlarised GLEAM Survey (POGS) 20m

Historically, the low-frequency linearly-polarised radio source population has remained largely unexplored. However, the advent of new instrumentation in the SKA Pathfinder and Precursor era, plus recent advances in supercomputing and data processing techniques, have enabled a renaissance in this field.

In this talk, I will present the results of the POlarised GLEAM Survey (POGS), our all-sky MWA Phase I Rotation Measure (RM) survey, which covers almost the entire Southern sky between Dec. -82 and Dec. +30 at a reference frequency of 200 MHz. I will present our catalogue of low-frequency detections of known pulsars, and what our precision RMs (typically more than an order of magnitude more precise than previous measurements) allow us to infer about the magnetised ISM of the Milky Way. I will also discuss the linear polarisation properties of the low-frequency extragalactic radio source population, including what the bulk properties of our sample can tell us about the magnetised IGM, and I will present for the first time an initial investigation of the low-frequency polarised radio source counts.

Speaker: Christopher Riseley (Alma Mater Studiorum - Universita di Bologna)
• 2:40 PM
An update on the GLEAM 4-Jy (G4Jy) Sample 20m

Speaker: Sarah White (SARAO - Rhodes University)
• 3:00 PM
Unexpected Spectral Variability at Low Frequencies 20m

Determining the origins of low-frequency (~MHz) variability of extragalactic sources has, until recently, largely been limited to small populations and/or single frequencies. Variability offers a unique opportunity to study both intrinsic properties of sources as well as the intervening media between source and observer. However, large population studies with significant spectral and temporal coverage have only recently become available with the development of radio telescopes like the Murchison Widefield Array (MWA). Using two epochs of the Galactic and Extragalactic All-sky MWA (GLEAM) survey, we have conducted a variability analysis of over 23,000 sources across 100—231MHz over a year-long timescale, the only spectral variability study of its kind. Contrary to expectations, we find a large sub-population of radio galaxies exhibiting large variation in flux density and spectral shape which cannot be explained entirely by either intrinsic or extrinsic mechanisms. Intrinsic origins, such as flaring active galactic nuclei (AGN), suggest a significant component of the flux density comes from the core/jet or evolution of these sources within one year. Extrinsic variability, such as refractive interstellar scintillation, suggests unexpected morphologies, like hot-spots or knots in the lobes of radio galaxies, contradictory to what we expect at low frequencies. Our measured variations suggest that low-frequency variability is more common than previously thought, and highlight the insufficient understanding of the emission mechanisms at low frequencies, and AGN evolutionary scenarios. In the SKA era, as large-scale, spectral variability surveys become achievable, rigorous statistics and understanding of the origins of low-frequency variability is needed. This study provides the first standardised methodology for future statistical analyses and classifications of low-frequency spectral variability.

Speaker: Kathryn Ross
• Friday, July 17
• 8:00 AM 9:00 AM
• 8:00 AM
MWA data life cycle and future plans 20m
Speaker: Greg Sleap (Curtin)
• 8:20 AM
Phase III Overview 20m
Speaker: Mia Walker (MWA)
• 8:40 AM
MWAX - New MWA correlator update and capabilities 20m

Progress continues with MWAX, the MWA’s new 256-tile fringe-stopping, real-time correlator and beamformer. Cross-validation of visibility outputs against the existing correlator continues. The benchmark performance for 256 tiles has been positive and has validated the planned architecture of 24 GPU-accelerated servers for the current receiver architecture. Parallel work towards possible new 'Phase 3' receivers with over-sampling channelisers, different coarse channels bandwidths and increased data rates is under way. The optimum network, GPU selection and server configuration to best utilise these possible new receivers is currently under evaluation together with logistical considerations such as physical locations of equipment and wide area network implications. Downstream tools are beginning to be updated to ingest MWAX visibility sets and first-light images have been successfully generated. Work also continues on the real-time beamformer, a single software component that can form multiple simultaneous beams, a mixture of multiple incoherent beams (of differing time/frequency resolutions) and multiple tied-array beams (of differing directions on the sky). Both the correlator and beamformer ingest data from the new high-time-resolution UDP multicast stream, a feature which also allows other high time resolution consumers (for example, Breakthrough Listen and perhaps in the future an FRB detection pipeline, or any number of novel real-time processing applications) to commensally tap into the MWA data stream with no impact to observations.

Speaker: Brian Crosse (Curtin)
• 9:00 AM 10:00 AM
Science: Phase III Discussion
Convener: Prof. Melanie Johnston-Hollitt (ICRAR/Curtin)
• 10:00 AM 10:20 AM
Coffee 20m
• 10:20 AM 11:20 AM
• 10:20 AM
Site Activity Update 20m
Speaker: Andrew McPhail
• 10:40 AM
Getting the MWA to produce the data you want 20m

In this talk, I won't try and tell you how to get a proposal accepted by the TAC. Instead, I'll talk about how to write 'Part C', the actual details of what you want the telescope to do, if the TAC accepts the proposal. As the person who turns accepted proposals into scheduled MWA observations, I'll describe what information I need, and how to present it in a way that makes my job easier, and helps let you get the best results out of the observations.

Speaker: Andrew Williams (MWA Telescope)
• 11:00 AM
Calibration database for the MWA ASVO 20m

In the last two years the MWA All-Sky Virtual Observatory (ASVO) has been enhanced by addition of the calibration database. This new extension has enabled a possibility of downloading calibrated data sets in standard radio-astronomy data formats (CASA measurement sets or UV FITS files) via the MWA ASVO web page or API. Therefore, allowing any researcher worldwide, without a detailed knowledge of the MWA telescope and data processing, to download calibrated visibility data and create images using standard radio-astronomy software packages. The database has been populated with calibration solutions since the inauguration of the MWA in 2013 using fully automated data processing pipelines, including a near-real-time pipeline, which automatically processes calibration observations shortly after their acquisition.

In this talk, I will present the calibration database, the pipelines and monitoring of long-term stability of the MWA calibration solutions enabled by the near-real-time pipeline.

Speaker: Marcin Sokolowski (Curtin University)
• 11:20 AM 12:00 PM
Science: Transients
• 11:20 AM
Transients Update 20m
Speaker: Paul Hancock
• 11:40 AM
Looking for cosmic rays with the MWA at 15ns time resolution 20m

Cosmic rays are the most extreme particles in the Universe and are detectable on Earth. The radio emission produced by cosmic rays when they interact with the Earth’s atmosphere is an excellent tracer of their properties. The low radio frequency interference environment of the Murchison Widefield Array (MWA) makes this instrument ideal for detecting and measuring this radio emission and therefore the study of high energy cosmic rays. From the radio information, the characteristics of the particle such as energy, incident direction, and species have to be reconstructed, aided by the use of air shower simulations. However, the pulses produced by these air showers occur on timescales of the order of 15 ns and the standard output time resolution of the MWA is 100 microseconds. In this talk, I present a new approach that reconstructs MWA voltages to a time resolution of 15 ns and I describe the results from the first detection run. This approach will not only enable the detection of cosmic rays but will also provide a new view of the radio environment of the Murchison Radio Observatory at these timescales.

Speaker: Alexander Williamson (Curtin Institute for Radio Astronomy)
• 12:00 PM 1:00 PM
Lunch 1h
• 1:00 PM 1:20 PM
Science: Transients
• 1:00 PM
Introduction of SHAO Transient Pipeline (STEP) 20m
Speaker: Zhijun Xu
• 1:20 PM 2:40 PM
Science: VCS
• 1:20 PM
VCS science update 20m

I will present an overview of the various scientific and technical development activities around the VCS (pulsar) science, with particular emphasis on the progress being made with the SMART pulsar survey, and the new projects that are being initiated around this initiative.

Speaker: Ramesh Bhat (Ramesh)
• 1:40 PM
Frequency-dependent polarisation in high time resolution studies of PSR B0031-07's single pulses 20m

The emission mechanism of radio pulsars is a long-standing and important open question in astrophysics. Although average pulse profiles can reveal global properties of pulsar magnetospheres, a successful theory emission mechanism must be able to explain the wide variety of phenomena seen at the single pulse level. We have leveraged the recent developments in the MWA-VCS software pipeline to observe PSR B0031-07 at a time resolution of ~50 us ($\nu\sim155\,$MHz, BW $= 30.72\,$MHz). This pulsar exhibits a range of interesting, well-studied single-pulse phenomena, including nulling, subpulse drifting, multiple drift modes, and (occasionally) "giant" pulses. In this talk, we showcase a variety of previously unobserved single-pulse phenomena, including frequency-dependent polarisation that may be the result of the coherent superposition of two orthogonal polarisation modes. Insofar as they can be shown to be truly intrinsic to the source, such observations can offer unprecendented insights into the pulsar emission mechanism.

Speaker: Sam McSweeney (CIRA, Curtin University)
• 2:00 PM
Dispersion measure investigation towards millisecond pulsars with the MWA 20m

With the ability to reconstruct high-time resolution voltage time series at microsecond ($\sim 0.78 \mu$s) time resolution and perform phase-coherent de-dispersion, it has become possible to obtain high-fidelity detections of millisecond pulsars (MSPs) with the MWA. In combination with the large frequency lever arm provided by the MWA this allows measuring pulsar dispersion measures (DMs) at very high precision – almost an order of magnitude better than those currently achievable at conventional timing frequencies ($\sim 1-2$ GHz) for pulsar timing array (PTA) experiments. A particularly interesting target is PSR J$2241$-$5236$, a short period ($2.18$ ms) MSP in a $3.5$-hour, almost circular orbit with a low-mass ($\sim 0.01$ M$_\odot$), white dwarf companion. In this talk, I will present results from our recent measurements from the MWA observations that span the full orbit, and analysis of DM variations to investigate any likely orbital modulations of DM that may be caused by the companion’s winds. I will also present new results from our recent multi-telescope observing campaign undertaken with the MWA, GMRT, and Parkes telescopes to investigate recently theorised chromaticity (frequency dependence) in pulsar DM, which is thought to arise as a consequence of multi-path propagation effects. Much of this analysis is focused on data for MSPs J$2241$-$5236$ and J$2145$-$0750$. These analyses and results also showcase the importance of low-frequency observations in the larger context of global PTA efforts.

Speaker: Dilpreet Kaur (Curtin University-ICRAR)
• 2:20 PM
MWA-VCS pulsar search and beamforming on CSKAP 20m
Speaker: Zhongli Zhang
• 2:40 PM 3:00 PM
Management: Wrap-up