2020 MWA Virtual Project Meeting

15 Jul 2020, 08:00 → 17 Jul 2020, 15:00 Australia/Perth

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)

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Watch the livestream/recordings

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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.

Wednesday, 15 July

08:00 → 10:00 Management: Board Meeting

10:00 → 10:20 Coffee

10:20 → 12:00 Management: Board Meeting

12:00 → 13:00 Lunch

13:00 → 15:00 Management: Board Meeting

Thursday, 16 July

08:00 → 08:40 Management: Welcome

08:00 Welcome by MWA Board Chair

Speaker: Stuart Wyithe

08:10 MWA Director's Report

Speaker: Melanie Johnston-Hollitt (ICRAR/Curtin)

08:30 Principal Scientist's Update

Speaker: Adam Beardsley

08:40 → 10:00 Science: EoR

08:40 Multi-redshift upper limits on the signal from the Epoch of Reionisation using the Murchison Widefield Array

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)

09:00 A Unified Calibration Framework for 21 cm Cosmology

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)

09:20 Measuring MWA Beam Shapes Using Satellites

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)

09:40 WODEN: An MWA specific GPU simulation code

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 → 10:20 Coffee

10:20 → 12:00 Science: SHI

10:20 SHI Update

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 The MWA IPS Phase-II Survey

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 First radio evidence for impulsive heating of the quiet solar corona

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 Probing fine spatial, temporal and spectral structures of the Sun

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 Solar flux density calibration with in-field sources for MWA solar observation

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 → 13:00 Lunch

13:00 → 15:20 Science: GEG

13:00 GEG Update

Speaker: Chenoa Tremblay

13:20 An MWA Phase II follow up of diffuse, non-thermal radio emission in galaxy clusters

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)

13:40 Dying radio galaxies as seen by MWA, ASKAP and ATCA

The jets produced by accretion onto super-massive black holes inflate into cocoons of shocked plasma (radio galaxies). While a majority of such sources have an active galactic nucleus, the central activity in a small fraction of radio galaxies switches off, giving rise to a dying radio galaxy. This talk presents the results of Quici et al. (in prep), which identifies a complete sample of active and dying radio galaxies using MWA, ASKAP and ATCA radio data. We discuss the challenges associated with identifying complete samples of dying radio galaxies. By considering the energetics (between ~100 MHz and 10 GHz), we present supporting evidence that dying radio galaxies fade rapidly once the AGN switches off. We constrain the fraction of dying radio galaxies, in a flux limited sample, between 6% and 12% and discuss the potential implications of these values in terms of the radio-loud AGN duty cycle. We present a peculiar dying radio galaxy candidate in which the morphology of the radio emission is in some tension with its spectral energy distribution, and discuss the possible evolutionary scenarios. Finally we discuss how complete samples of radio galaxies, such as that used for this study, can be used to probe the duty cycle of radio-loud AGN.

Speaker: Benjamin Quici (Curtin University for Radio Astronomy (CIRA))

14:00 Centaurus A like you have never seen it before

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

14:20 All-sky results from the POlarised GLEAM Survey (POGS)

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)

14:40 An update on the GLEAM 4-Jy (G4Jy) Sample

Radio-loud active galactic nuclei (AGN) feature heavily in our understanding of galaxy evolution. However, when it comes to studying their properties as a function of redshift and/or environment, the most-detailed studies tend to be limited by small-number statistics. In this talk, we will give an update on this new sample of 1,863 of the brightest radio-sources in the southern sky (Dec. < 30 deg). These were observed at low radio-frequencies as part of the GaLactic and Extragalactic All-sky MWA (GLEAM) survey, conducted using the Murchison Widefield Array (MWA). This instrument allows us to select radio-loud AGN in an orientation-independent way (i.e. minimising the bias caused by Doppler boosting, inherent in high-frequency surveys). In addition, the location of the MWA in a protected, radio-quiet zone means that we have excellent spectral coverage, with 20 flux-density measurements spanning a frequency range of 72-231 MHz. We have made a compilation of radio sources with integrated flux-density > 4 Jy at 151 MHz, which we refer to as the GLEAM 4-Jy (G4Jy) Sample (White et al., 2020a, 2020b). Following repeated visual inspection (using multi-wavelength information) and thorough checks against the literature, the G4Jy catalogue is now publicly available (see https://github.com/svw26/G4Jy), and includes mid-infrared identifications for 86% of the sources. For 129 sources, there is ambiguity concerning candidate host-galaxies, and this includes four sources (B0424−728, B0703−451, 3C 198, and 3C 403.1) where we question the existing identification. These ‘ambiguous’ sources have been followed-up using MeerKAT Open Time (PI: White), and we will present a few of those that have been re-imaged recently. With over 10 times as many sources as the best-studied, low-frequency radio-source sample that is optically complete (the revised Third Cambridge Catalogue of Radio Sources; 3CRR), the G4Jy Sample will allow models of radio-loud AGN to be tested more robustly.

Speaker: Sarah White (SARAO - Rhodes University)

15:00 Unexpected Spectral Variability at Low Frequencies

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, 17 July

08:00 → 09:00 Engineering & Operations: Upgrades

08:00 MWA data life cycle and future plans

Speaker: Greg Sleap (Curtin)

08:20 Phase III Overview

Speaker: Mia Walker (MWA)

08:40 MWAX - New MWA correlator update and capabilities

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)

09:00 → 10:00 Science: Phase III Discussion

Convener: Prof. Melanie Johnston-Hollitt (ICRAR/Curtin)

10:00 → 10:20 Coffee

10:20 → 11:20 Engineering & Operations: Updates

10:20 Site Activity Update

Speaker: Andrew McPhail

10:40 Getting the MWA to produce the data you want

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 Calibration database for the MWA ASVO

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 → 12:00 Science: Transients

11:20 Transients Update

Speaker: Paul Hancock

11:40 Looking for cosmic rays with the MWA at 15ns time resolution

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 → 13:00 Lunch

13:00 → 13:20 Science: Transients

13:00 Introduction of SHAO Transient Pipeline (STEP)

Speaker: Zhijun Xu

13:20 → 14:40 Science: VCS

13:20 VCS science update

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)

13:40 Frequency-dependent polarisation in high time resolution studies of PSR B0031-07's single pulses

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)

14:00 Dispersion measure investigation towards millisecond pulsars with the MWA

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)

14:20 MWA-VCS pulsar search and beamforming on CSKAP

Speaker: Zhongli Zhang

14:40 → 15:00 Management: Wrap-up