MWA Virtual Project Meeting - June 2021

22 Jun 2021, 08:00 → 23 Jun 2021, 15:20 Australia/Perth

Dear all, dates have been announced for the mid-2021 project meeting:

Time Zone / Location	Project Meeting Day #1	Project Meeting Day #2
Providence/Toronto   (GMT- 4)	21 June, 2000-0300	22 June, 2000-0300
Bologna (GMT+2)	22 June, 0200-0900	23 June, 0200-0900
Perth/Shanghai (GMT+8)	22 June, 0800-1500	23 June, 0800-1500
Tokyo (GMT+9)	22 June, 0900-1600	23 June, 0900-1600
Melbourne (GMT+10)	22 June, 1000-1700	23 June, 1000-1700

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 will 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.  

Tuesday, 22 June

08:00 → 09:00 Management: Welcome - Day 1

08:00 Welcome by MWA Board Chair

Speaker: Stuart Wyithe

08:10 Director's Report

Speaker: Prof. Steven J. Tingay (Curtin Institute for Radio Astronomy)

08:40 Principal Engineer Update

Speaker: Prof. Randall Wayth (Curtin University)

09:00 → 10:00 Engineering & Operations: Upgrades & Updates

09:00 MWAX Update

Abstract TBA

Speakers: Dr Ian Morrison (ICRAR/Curtin), Brian Crosse (Curtin)

09:20 MWA ASVO and Archive Update

In this talk, we present that latest updates and plans for the MWA ASVO data portal, the state of the MWA Archive and the latest updates from the Pawsey Supercomputing Centre.

Speakers: Greg Sleap (Curtin University/Murchison Widefield Array), Harrison Barlow

09:40 Telescope Monitor & Control

Updates on the M&C front, and what it means for MWA astronomers

Speaker: Andrew Williams (MWA Telescope)

10:00 → 10:20 Coffee

10:20 → 11:00 Engineering & Operations: Upgrades & Updates

10:20 Verifying the proposed signal processing architecture for future MWA upgrades

The proposed signal processing architecture for the next phase of the MWA consists of number of improvements including a new over-sampled coarse PFB and an FFT based ultra-fine channeliser. This architecture is designed to eliminate aliasing at the coarse channel edges, a problem that continues to plague MWA data to this day. Strict requirements, particularly those for EoR science, impose limits on the extent that systematic errors can contaminate the spectrum after 100 hours of integration. Therefore, we conducted an experiment that emulates the full signal chain within the lab and integrated the data for a duration of 100 hours. I present the findings from this experiment and our progress towards verifying the new architecture can meet these requirements.

Speaker: Mr Jake Jones (ICRAR - Curtin University)

10:40 Site Update

Speaker: Andrew McPhail

11:00 → 11:30 Discussion

11:30 → 12:30 Lunch

12:30 → 14:30 Science: EoR

12:30 EoR Update

Speaker: Cathryn Trott (ICRAR - Curtin University)

12:50 hyperdrive: New MWA calibration software

hyperdrive is a spiritual successor to the Real-Time System (RTS) calibration software commonly employed by the MWA EoR team, but with a focus on usability, testing and efficiency. It currently operates similar to André Offringa's calibrate program, but is 2-3x faster and supports many more input and output formats. At the time of writing, comparisons with the RTS are forthcoming, although it is anticipated that the calibration results are comparable while completing calibration faster and using 25x fewer GPU-equipped-supercomputer nodes. Also of note is that it is written in Rust, not C++, and supports using GPUs for further accelerated processing. The homepage is here: https://github.com/MWATelescope/mwa_hyperdrive

In this talk, I will detail why hyperdrive exists, its design philosophy, and its next steps over the coming years.

Speaker: Dr Christopher Jordan (Curtin University )

13:10 159MHz Spherical Harmonic Diffuse Southern Sky Map Created with the Engineering Development Array (EDA2)

One of the major priorities of international radio astronomy is to study the early
universe through the detection of the 21 cm HI line from the Epoch of Reionisation
(EoR). Due to the weak nature of the 21 cm signal, an important part in the detection of the EoR is removing contaminating foregrounds from our observations as they are multiple orders of magnitude brighter. One method to achieve this is through the generation of sky maps spanning a wide range of frequencies and angular scales to filter out these contaminants. Complementing the existing low-frequency sky maps, we have constructed a Southern Sky map with the Engineering Development Array (EDA2), one of the Square Kilometre Array (SKA) prototype systems. This is achieved through spherical harmonic transit interferometry; employing the m-mode formalism. Our results show that we can accurately map emissions on a multitude of angular scales by constraining the parameters in generating the spherical harmonic modes. This sky map is the first in a series of SKA precursor sky maps and serves as an initial step towards the creation of a well constrained and characterised diffuse foreground model.

Speaker: Mr Mike Kriele (International Centre for Radio Astronomy Research (ICRAR), Curtin University; ARC Centre of Excellence for All-Sky Astrophysics in 3 Dimensions; Eindhoven University of Technology)

13:30 Ionospheric effects on MWA Epoch of Reionisation observations.

The Epoch of Reionisation (EoR) is the period within which the neutral universe transitioned to an ionised one. This period remains unobserved using low-frequency radio interferometers which target the 21 cm signal of neutral hydrogen emitted in this era. The Murchison Widefield Array (MWA) radio telescope was built with the detection of this signal as one of its major science goals. One of the most significant challenges towards a successful detection is that of calibration, especially in the presence of the Earth's ionosphere. By introducing refractive source shifts, distorting source shapes and scintillating flux densities, the ionosphere is a major nuisance in low-frequency radio astronomy. We introduce SIVIO, a software tool developed for simulating observations of the MWA through different ionospheric conditions estimated using thin screen approximation models and propagated into the visibilities. This enables us to directly assess the impact of the ionosphere on observed EoR data and the resulting power spectra. We show that the simulated data captures the dispersive behaviour of ionospheric effects. We then investigate the effects of different ionospheric turbulence levels and spatial structure on the 21 cm power spectrum both in simulations and observed MWA data, as well as, improved methods in MWA ionospheric calibration. In turn, this will inform on the best strategies of identifying and efficiently eliminating ionospheric contamination in EoR data moving into the Square Kilometre Array era.

Speaker: Kariuki Chege (Curtin University)

13:50 The Long Baseline Epoch of Reionisation Survey -- Improved models for MWA EoR0 Field

One of the principal systematic constraints on the Epoch of Reionisation (EoR) experiment is the accuracy of the foreground calibration model. Recent results have shown that highly accurate models of extended foreground sources, and including models for sources in both the primary beam and its
sidelobes are necessary for reducing foreground power. To improve the source models in the EoR fields observed by the Murchison Widefield Array (MWA), we conducted the Long Baseline Epoch of Reionisation Survey (LoBES). This survey consists of multi-frequency observations of the main MWA EoR fields and their eight neighbouring fields using the MWA Phase II extended array. We present the results of the first half of this survey centred on the MWA EoR0 observing field (centred at RA (J2000) 0 h , Dec (J2000) −27 ◦ ). This half of the survey covers an area of 3069 sq-deg, with an average rms of 2.1 mJy/beam. The resulting catalogue contains a total of 80824 sources, with 16 separate spectral measurements between 100 and 230 MHz, and spectral modelling for 78% of these sources. Over this region, we estimate that the catalogue is 90% complete at 32 mJy, and 70% complete at 10.5 mJy. Testing the performance of the new source models we measure lower residual rms values for peeled sources, particularly for extended sources, in a set of MWA Phase I data. For simulated MWA data, there is a factor of 3 improvements in the removal of foreground power on all angular scales in the 2-dimensional power-spectrum. In both data and simulation, it is clear that the LoBES sky models significantly improve upon the current sky model used by the Australian MWA EoR group for the EoR0
field.

Speaker: Christene Lynch (ICRAR-Curtin/ASTRO3D)

14:10 MWA Japan Science Update

In this talk, we will show recent science updates from MWA Japan. In particular, we first highlight the MWA ultralow (75-100 MHz) data analysis. In this work, using 15 hours of MWA Phase I data, we analyzed the systematics related to the ultra-low frequency observation such as the ionosphere and RFI. Based on the careful investigation, we selected 6 hours of clean datasets, and the best upper limits have been obtained on the 21cm power spectrum at z=15. We also show theoretical prediction for the constraints on the AGN luminosity function from the 21cm line imaging by assuming the MWA observation. As AGNs create a unique 21cm line profile, we can count the number of the AGNs at high redshift. Using the number of AGNs, we can constrain the model of AGN luminosity function. Finally, we will briefly introduce on-going projects.

Speaker: Shintaro Yoshiura (NAOJ)

Wednesday, 23 June

08:00 → 08:20 Management: Welcome - Day 2

08:00 Principal Scientist Update

Speakers: Christopher Riseley (Alma Mater Studiorum - Universita di Bologna), Benjamin McKinley (Curtin University)

08:20 → 09:50 Science: GEG

08:20 GEG Update

Speaker: Chenoa Tremblay (CSIRO)

08:40 GLEAM-X Update

The successor to the GaLactic and Extragalactic All-sky MWA (GLEAM) survey, GLEAM-eXtended uses the Phase II extended configuration of the MWA to survey the GLEAM sky at twice the resolution and up to an order of magnitude higher sensitivity. In 2020 we completed observations across the entire southern sky. The team is finalising the first data release, covering 2,000 square degrees, down to an RMS noise level of <1.5 mJy/beam in all Stokes parameters. We cover 72 — 231 MHz, illuminating the low-frequency behaviour of over 100,000 radio sources, and also perform searches for new polarised sources. Through creating the first data release we have learned valuable lessons on calibration and ionospheric behaviour, which we would like to share with the collaboration. The initial data release will be available for early science within the collaboration, pending publication later this year.

Speakers: Natasha Hurley-Walker (Curtin / ICRAR), Xiang Zhang (CSIRO Astronomy & Space Science)

09:10 The GLEAMing of the first supermassive black holes: a combined MWA/LOFAR study to constrain low-frequency spectral turnover

High-redshift radio galaxies are vital laboratories for studying massive galaxy formation and evolution in the early Universe (review by Miley & De Breuck 2008). We have developed a new selection technique for finding these rare, powerful systems, making use of spectral curvature in the Murchison Widefield Array (MWA) 72-231 MHz GLEAM survey (Hurley-Walker et al. 2017; Franzen et al. 2021). In a pilot study of four sources in the 60 deg$^2$ GAMA-09 field, we discovered the second-most distant radio galaxy currently known (GLEAM J0856 at redshift z = 5.55; Drouart et al. 2020), with the possibility that a second source is also at z > 5 (GLEAM J0917; Drouart et al. 2021, submitted). While GLEAM offers excellent coverage of the low-frequency radio spectrum of both J0856 and J0917, we have combined these data with Low-Frequency Array (LOFAR) 34-66 MHz observations to better constrain the spectral curvature properties, search for and model a spectral turnover, and assess the accuracy of low-frequency flux density scales. By identifying the mechanism(s) responsible for a spectral turnover, we will gain new insights into the physical conditions at the end of, and possibly during, the Epoch of Reionisation.

Speaker: Jess Broderick (ICRAR/Curtin)

09:30 Synchrofit: a python-based synchrotron spectral fitting code

For this talk I will present synchrofit (synchrotron fitter), which implements a reduced dimensionality parameterisation of standard synchrotron spectrum models, and provides fitting routines applicable for active galactic nuclei and supernova remnants. The Python code includes the Jaffe-Parola model (JP), Kardashev-Pacholczyk model (KP), and continuous injection models (CI/KGJP) for both constant or Maxwell-Boltzmann magnetic field distributions. An adaptive maximum likelihood algorithm is invoked to fit these models to multi-frequency radio observations; the adaptive mesh is customisable for either optimal precision or computational efficiency. Principally, synchrofit is designed to parameterize an integrated radio spectrum by physical properties such as the injection index, break frequency, and (if applicable) the remnant fraction. With knowledge of redshift and magnetic field, these quantities can then be related to the spectral age of the emission (which synchrofit provides functions for). I also show how synchrofit can be adapted to produce spatially-resolved spectral age maps.

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

09:50 → 10:10 Coffee

10:10 → 11:10 Science: Transients

10:10 Transients Update

Speaker: Paul Hancock

10:30 Space Surveillance Using the Murchison Wide-field Array

The growing number of Low Earth Orbit (LEO) objects has been an increasing concern for the Space Domain Awareness (SDA) community and the astronomy community. While the rapidly increasing number of satellites demands the development of a wide field-of-view SDA sensors that is capable of performing simultaneous detections, many recent studies have also highlighted the importance of understanding the near-earth environment for astronomy in optical, infrared, and radio wavelengths. Hence, we address these issues by using a low-frequency radio-interferometer, the Murchison Widefield Array (MWA), to perform space surveillance using passive radar techniques, whilst understanding its impact on FM band observations performed from the Murchison Radio-Observatory (home to the MWA and the future low-frequency Square Kilometer Array). In this talk, I will summarise the non-coherent passive radar capability developed using the MWA. We have developed and tested a LEO blind detection pipeline on archived MWA data, and we detect over 70 unique objects over multiple passes, demonstrating the MWA to be a valuable addition to the global SDA network. We detect LEO objects as small as 0.03 m2 radar cross-section and as far as ~1000 km. Additionally, we also detect FM reflections from Geminid meteors and aircrafts flying over the MWA. For many of the nearby detected objects, we split the MWA into two sub-arrays and perform line-of-sight range measurements using the parallax method. As part of this analysis, we show that the standard MWA RFI flagging strategy misses most of this RFI and that this should be a careful consideration for the SKA. We also demonstrate orbit determination and LEO catalog maintenance capability using the MWA, and the obtained orbital elements are in good agreement with the publicly released orbital elements by the Space Surveillance Network (SSN). Based on our understanding of the MWA SDA system, I conclude the talk by briefly describing the methods to mitigate the impact of FM reflecting LEO satellites on radio-astronomy observations, and how maintaining a catalog of FM reflecting LEO objects is in the best interest of both SDA and radio-astronomy.

Speaker: Steve Prabu (Curtin University)

10:50 SETI Opportunities with the MWA

The Search for Extraterrestrial Intelligence (SETI) kicked off in 1960, when Frank Drake turned the Tatel telescope toward nearby stars to search for 'technosignatures' that would indicate intelligent life beyond Earth. While SETI searches have been running ever since -- including several searches of archival MWA image cubes -- the low-frequency radio sky remains under-explored. In this talk, we discuss SETI opportunites for the MWA: an ideal instrument for low-frequency technosignature searches. I will discuss opportunites to use archival data (e.g. GLEAM), and how higher-resolution data from the upgraded MWAX correlator could greatly improve sensitivity to narrowband signals. I will also detail our collaboration with Breakthrough Listen, in which we are setting up a commensal system to run realtime, ultra-fine resolution (~Hz) searches of MWA beamformed data. I will report on progress on this system to date, initial results, and forecasts for future surveys.

Speaker: Danny Price (ICRAR/Curtin)

11:10 → 12:10 Science: VCS

11:10 VCS Update

Speaker: Ramesh Bhat (Dr)

11:30 Pulsar polarimetry with the MWA

Pulsars are highly linearly polarised sources whose polarimetry contains a wealth of information about the poorly-understood pulsar radio emission mechanism and the dynamics of the turbulent, relativistic plasma that gives rise to it. However, in order to leverage this information for scientific gain, the polarimetric response of the telescope must be precisely understood. While much fruitful work has been done to understand MWA polarimetry, the use of pulsars as potential polarimetric calibrators has not been fully explored. In this talk, I will discuss how the MWA's Voltage Capture System observations of bright pulsars might be used to improve existing calibration techniques by modelling, and correcting for, polarisation leakage.

Speaker: Dr Sam McSweeney (CIRA, Curtin University)

11:50 The Southern-sky MWA Rapid Two-metre (SMART) pulsar survey. First discoveries and the low-frequency pulsar population

One of the unsolved problems of pulsar physics is the discrepancy between the neutron star birth rate derived from core-collapse supernova rates, and that derived from the observed radio pulsar populations. One method to increase the accuracy of our pulsar population simulations is to improve our understanding of the relatively unexplored low-frequency parameter space.

The Southern-sky MWA Rapid Two-meter (SMART) pulsar survey has made its first pulsar discovery, PSR J0036-1033, after processing only $\sim$1% of data. I will discuss how this discovery, along with the survey's growing number of detections of other, known pulsars, informs pulsar population statistics.

Speaker: Nicholas Swainston (Curtin University)

12:10 → 13:10 Lunch

13:10 → 14:30 Science: SHI

13:10 Solar Update

I will present a brief overview of the recent work by MWA Solar group. The aspects covered will range from work on developing the next version solar imaging pipeline which will have the capability to make full Stokes images on the tools and technique development front, to sharing the current status of our ongoing investigations on characterizing the Weak Impulsive Narrowband Quiet Sun Emissions (WINQSEs), which likely hold a tantalizing clue to coronal heating. I will also touch upon our recent work on the discovery of quasi-periodic pulsations (QPPs) in solar active emissions across a large range of flux densities and its implications.

Speaker: Divya Oberoi (National Centre for Radio Astrophysics, Pune India)

13:30 Insights from snapshot spectroscopic radio observations of a weak Type I solar noise storm

We present a high fidelity snapshot spectroscopic radio imaging study of a weak type I solar noise storm which took place during an otherwise exceptionally quiet time. Using high fidelity images from the Murchison Widefield Array, we track the observed morphology of the burst source for 70 minutes and identify multiple instances where its integrated flux density and area are strongly anti-correlated with each other. The type I radio emission is believed to arise due to electron beams energized during magnetic reconnection activity. The observed anti-correlation is interpreted as evidence for presence of MHD sausage wave modes in the magnetic loops and strands along which these electron beams are propagating. Our observations suggest that the sites of these small scale reconnections are distributed along the magnetic flux tube. We hypothesise that small scale reconnections produces electron beams which quickly get collisionally damped.
Hence, the plasma emission produced by them span only a narrow bandwidth and the features seen even a few MHz apart must arise from independent electron beams.
We also find tentative evidence for these small scale reconnections in the AIA maps, substantiating the presence of discernible reconnection activity at the noise storm site even during its quiescent phase.

Speaker: Dr Surajit Mondal (National Centre for Radio Astrophysics, Tata Institute of Fundamental Research)

13:50 Imaging of weak impulsive solar emissions using residual visibilities

Energetically weak bursts contribute most to the solar plasma heating. However, they are difficult to image accurately due to the thermal background from the active region. Broadly, we can distinguish the emission from radio bursts consisting of slowly varying components and transient burst components. To characterise the burst component, we must take out the slowly varying components by subtracting the visibilities of quiet times. For the observations of bursts spanning several hours, removing one static component is too simplistic as the active region's background emission changes in many hours. In this work, we subtract a visibility continuum that quantifies the slowly varying component. This is done by identifying several quiet periods within the observations, later fitting it with an appropriate degree of the polynomial. The residual visibility dataset can be used to image transient burst components and characterise their strength, location and occurrence. By employing this method for an MWA dataset, we have been able to image transient emission up to 10^4 K brightness temperatures.

Speaker: Rohit Sharma (University of Applied Sciences Northwestern Switzerland)

14:10 IPS and Ionospheric Scintillation measurements with the MWA

I will give an update on our Interplanetary Scintillation (IPS) project, in particular the finalised IPS catalogue consisting of over 5000 sources. I will describe the latest comparison with International Lofar, and our efforts to use these more conventional interferometric measurements to calibrate our IPS measurements, and how we might also attempt more detailed mapping of sub-arcsecond source structure.

More broadly we have been applying our IPS technique to EoR observations in order to understand ionospheric scintillation; both as an interesting phenomenon in its own right, and as a potential contaminant in other radio measurements, especially IPS. Early indications are that IPS is significant, and that ionospheric scintillation has a magnitude in line with predictions ($\sim$1% - $\sim$10% scintillation indices). However it is only weakly correlated with other indicators of ionospheric activity.

Speaker: John Morgan

14:30 → 14:40 Management: Wrap Up

14:30 Wrap Up

Speaker: Prof. Steven J. Tingay (Curtin Institute for Radio Astronomy)