MWA Project Meeting - July 2022

20 Jul 2022, 08:00 → 21 Jul 2022, 15:20 Australia/Perth

Dear all,

We are pleased to announce the 2022 mid-year MWA Project Meeting, on July 20-21.

This two-day event will focus on early career researcher science with the MWA.

The program will have sessions hosted at local hubs and broadcast online via the video conferencing software Webex. The talks will also be recorded and stored on the MWA's Youtube channel.

Please register your attendance and view the meeting timetable using the links on the side menu.

Wednesday, 20 July

08:00 → 08:50 Management: Welcome and Overview

08:00 Welcome by Board Chair

Speaker: Phil Edwards

08:10 MWA Director's Update

Speaker: Steven Tingay

08:30 Principal Scientist's Update

Speakers: Christopher Riseley, Ben McKinley

08:50 → 10:25 Science: EoR

08:50 EoR Analysis Bonanza

Systematics and foregrounds cloud the Epoch of Reionisation (EoR) measurement, and thus the EoR team focuses on building, developing, and publishing mitigation methods. A lot of recent effort into decreasing these systematics has been pushed into simulations like WODEN by Jack Line, calibration pipelines like hyperdrive by Chris Jordan, and smooth kernel implementations in FHD by Nichole Barry. We present preliminary results on combining these new methodologies together to decrease systematics on the EoR measurement using MWA data.

Speaker: Nichole Barry (Curtin University)

09:10 Uncovering the detailed antenna bandpass using MWAX

As spectral calibration precision is the greatest limiting factor for EoR science, understanding individual antenna behavior is crucial. The new MWAX correlator provides a unique opportunity to examine antenna spectral shape without the nonlinearities and other digital artifacts present in Legacy correlator data. By removing coarse channel polyphase filter shapes and cable reflections we uncover the underlying antenna bandpass as well as some unexpected residual digital artifacts. This work reveals a diversity of bandpasses with previously unseen features, informing new directions in precision calibration for EoR and other science.

Speaker: Pyxie Star (University of Washington)

09:30 (Multi-system) Spherical Harmonic Transit Interferometry

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 159 MHz Southern Sky map with the Engineering Development Array (EDA2), one of the Square Kilometre Array (SKA) prototype systems using Murchison Widefield Array (MWA) dipoles. This is achieved through spherical harmonic transit interferometry, using ARTEmIS: the All-Sky Telescope m-mode Imaging Suite. Our results show that we can accurately map emissions on a multitude of angular scales and with temperature scales that are in agreement with other well-established low-frequency sky maps. Furthermore, we introduce multi-system spherical harmonic transit interferometry; where multiple arrays and their observations can be combined to form a complete radio continuum image, without the need for ad-hoc regression.

Speaker: Mike Kriele (ICRAR - Curtin University/UWA)

10:00 Foreground Removal with Gaussian Process Regression

Observing the Epoch of Reionization(EoR) through the redshifted 21-cm line of Hl will revolutionize the study of the first stars, galaxies, and intergalactic medium in the early Universe. This signal carries the information on the fraction of neutral hydrogen, spin temperature, CMB temperature, and cosmological parameters. The redshifted 21-cm line is, however buried under foregrounds that are many orders of magnitude brighter. We must eliminate the foreground signals accurately.

One of the methods to remove foregrounds is Gaussian Process Regression(GPR). This method will statistically separate the 21cm line from most foregrounds and other contaminants. Mertens et al. 2020 show that GPR is capable for removing foregrounds on Low-Frequency Array (LOFAR).
In this talk, we show the result of foreground removal using GPR to Murchison Widefield Array (MWA) observation data.

Speaker: Takumi Ito

10:25 → 10:45 Coffee

10:45 → 12:30 Science: PFT/Transients

10:45 Science update: Pulsars and Fast Transients

I will give an overview of recent activities and updates on the pulsars and fast transient science theme within MWA science, including the progress being made with the SMART pulsar survey project, the VCSbeam development for enabling science with MWAX VCS, and other highlights from the pulsars and fast transient projects with the MWA.

Speaker: Ramesh Bhat (Dr)

11:15 The discovery of new VCS pulsars in dense stellar environments

I am happy to report some progress from Shanghai Astronomical Observatory, which is contineously in deep collaboration with the MWA observatory. With the archival MWA-VCS data and the computational platform of China SKA regional prototype in SHAO, we got preliminary results of the discovery of new pulsars in dense stellar environment, which is considered to be difficult in low-frequency radio observations. One is the re-detection of five "FAST" GCpsrs and the discovery of a possible new GCpsr in M2, and one is along the sight of the galactic bulge with both X-ray and optical counterparts. Our discoveries prove the ability of MWA-VCS, that low-frequency time-domain astronomy may do more than what we thought to be.

Speaker: Zhongli Zhang (Shanghai Astronomical Observatory)

11:35 pulsar_spectra: an open source flux density catalogue and pulsar spectra fitting software

We present the pulsar_spectra software repository, an open-source pulsar flux density catalogue and automated spectral fitting software that finds the best spectral model and produces publication-quality plots. The Python-based software includes features that enable users in the astronomical community to add newly published spectral measurements to the catalogue as they become available. This project is an example of how you can be a collaborative member of the astronomical community through software development.

Speaker: Nicholas Swainston (Curtin University)

11:45 SMART discovery of an unusual nulling, sub-pulse drifting pulsar

We announce the independent discovery of PSR J0027-1956 with the Murchison Widefield Array (MWA) in the ongoing Southern-sky MWA Rapid Two-meter (SMART) pulsar survey. J0027-1956 is an intermittent pulsar, with a nulling fraction of ~77%. This pulsar highlights the advantages of the survey's long dwell times (~80 min), which, when fully searched, will be sensitive to the expected population of similarly bright, intermittent pulsars with long nulls. A single-pulse analysis in the MWA's 140-170 MHz band also reveals a complex sub-pulse drifting behavior, including both rapid changes of the drift rate characteristic of mode switching pulsars, as well as a slow, consistent evolution of the drift rate within modes. The combination of nulling and sub-pulse drifting properties make this pulsar an ideal test bed for prevailing models of drifting behavior such as the carousel model.

Speaker: Sam McSweeney (CIRA, Curtin University)

12:05 Spectral evolution of pulsar radio emission using SKA-Low precursor stations

With their broad range of applications from performing exquisite tests of strong-field gravity to detecting ultra-low-frequency gravitational waves, pulsars are a key science driver for the Square Kilometre Array (SKA). Pulsar radio emission properties in the low-frequency band of the SKA (50-350 MHz) remain underexplored, yet are important for furthering our understanding of the detectable population of pulsars with the SKA and its pathfinders. Of particular interest are features such as a spectral flattening or turn-over that may occur at frequencies below 400 MHz, which will inform population studies and pulsar science planned with the low-frequency SKA (SKA-Low). In an effort to explore this, we have undertaken low-frequency studies of a modest sample of southern pulsars using the two precursor stations now operational at the Murchison site, where the SKA-Low will be built. The high-time resolution capabilities of these stations have been used to perform an initial census of the southern pulsar population, and observations were made at multiple spot frequencies across 70-350 MHz. Flux densities were measured using both the stations, and the spectra were modelled using robust fitting methods. Our analysis reveals low-frequency spectral features for a vast majority of pulsars, and for 16 pulsars we present updated spectral models. With a five-fold increase in sensitivity expected from the ongoing upgrade, it will become feasible to study a much larger sample of pulsars, the results from which will inform large-scale pulsar surveys planned with the SKA. This early demonstration of pulsar detection capabilities of SKA-Low stations suggests a promising future for low-frequency pulsar astronomy even in the early science phase of SKA-Low.

Speaker: Christopher Lee (Curtin University)

12:30 → 13:00 Science: Highlight Talk

12:30 Detection of frequency-dependent dispersion measures toward PSR J2241-5236 from contemporaneous wide-band observations

Making precise measurements of pulsar dispersion measures (DMs) and applying suitable corrections for them is one of the major challenges in pulsar timing arrays (PTAs). While the advent of wide-band pulsar instrumentation can enable more precise DM measurements and thence improved timing precision, it also necessitates careful assessments of frequency-dependent (chromatic) DMs that was theorised by Cordes et al. (2016). We present the detection of such an effect in our broadband observations of the millisecond pulsar PSR J2241-5236, a high-priority target for current and future PTAs. The observations were made contemporaneously using the wide-band receiver capabilities now available at the Murchison Widefield Array (MWA), the upgraded Giant Metrewave Radio Telescope (uGMRT), and the Parkes (Murriyang) telescopes, thus providing an unprecedentedly large frequency coverage from 80 MHz to 4032 MHz. Our analysis has revealed measurable changes in DMs that scale with the observing frequency. We discuss the potential implications of such a frequency dependence in the measured DMs, and the likely impact on the timing noise budget, and comment on the usefulness of low-frequency observations for advancing PTA efforts.

Speaker: Dilpreet Kaur (Curtin University-ICRAR)

Thursday, 21 July

08:00 → 08:25 Science: SHI

08:00 Imaging-spectroscopy of a band-split type II solar radio burst with the Murchison Widefield Array

Type II solar radio bursts are believed to be caused by magnetohydrodynamics (MHD) shock-accelerated electrons in the solar corona. Often type IIs exhibit fine structures in their dynamic spectra. For example, both fundamental and harmonic bands of type II bursts are split into two sub-bands. This is generally believed to be coming from upstream and downstream regions of the shock; however, this explanation remains unconfirmed. Here we present results from imaging analysis of type II radio burst band-splitting and fine structures observed by the Murchison Widefield Array (MWA) on 2014-Sep-28. The MWA provides high-sensitivity imaging spectroscopy in the range of 80-300 MHz with a time resolution of 0.5 s and a frequency resolution of 40 kHz. Our analysis provides rare evidence that band-splitting is caused by emission from multiple parts of the shock (as opposed to the upstream/downstream hypothesis). We also examine the small-scale motion of type II fine structure radio sources in MWA images. We suggest that this small-scale motion may arise due to propagation effects from coronal turbulence, and not because of the physical motion of the shock location. The study of the systematic and small-scale motion of fine structures may therefore provide a measure of turbulence in different regions of the shock and corona.

Speaker: Shilpi Bhunia (Trinity College Dublin)

08:25 → 09:05 Science: GEG

08:25 Precision Map of Diffuse Galactic Emission Across the Southern Galactic Cap

We present the recently published full Stopes map of galactic diffuse emission across 11k square degrees of the Southern galactic cap. While observed and processed under the auspices of the MWA EoR collaboration, we think this map might be of scientific interest to the wider MWA astrophysics community. Features include deep removal of extra-galactic sources, complete coverage on 1-9 degree scales, and careful calibration and processing so accurate scientific comparisons can be made across instruments and wavebands.

Speaker: Miguel Morales (University of Washington)

08:45 Using low frequency variability to find frustrated AGN

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). We have conducted a spectral variability survey of 15 sources over 72MHz to 10GHz using simultaneous observations with the MWA and the ATCA over a year. We will present the results of this survey which detects small scale structures (~mas scales) within AGN despite the low resolution of the ATCA and MWA (arcsecond to arcminute), confirmed with images using the LBA. In this talk we will discuss the power of spectral variability for determining morphologies and absorption mechanisms for compact peaked spectrum AGN which has been otherwise inconclusive.

Speaker: Kathryn Ross (ICRAR - Curtin University)

09:05 → 10:30 Engineering & Operations: Updates

09:05 Principal Engineer's Update

Speaker: Randall Wayth

09:30 The Dragons of Direction Dependent Calibration

With the success of Chris Jordan’s fast, consistent, and user-friendly implementation of direction independent calibration, Hyperdrive has seen a surge in popularity amongst astronomers looking to calibrate data from observations made with the new MWAX correlator, delivering noticeable improvements in calibration quality compared to its predecessors. Finally, we are ready to tackle the challenge of direction dependent calibration.

Dev will dissect the road ahead, unravelling the concepts behind each component in detail to compare the approaches of existing pipelines.

Speaker: Dev Null (Curtin)

09:55 MWA-ASVO Update

Speaker: Harrison Barlow

10:10 Data Retention

Speaker: Greg Sleap

10:30 → 10:50 Coffee

10:50 → 11:50 Discussion block - MWA Archive

Speaker: Greg Sleap

11:50 → 12:00 Management: Wrap-up

11:50 Wrap-up

Speaker: Steven Tingay