2022-A and 2022-B, Extended

The telescope will be in the long baseline (extended) configuration for the duration of the 2022-A and 2022-B observing periods.

Accepted allocations of observing time are detailed below for the 2022-A period (May 1, 2022 to September 30, 2022). There will be no formal Call for Proposals for 2022-B; instead, all observations will be using Director's Discretionary Time (DDT), subject to availability of the array. Applications for DDT proposals can be submitted at any time to the MWA Director (following the CfP template, with Parts B through D answered in brief).

Approved Proposals




Science Theme



Visibility Time Requested


VCS Time Requested



Rapid-response MWA observations of UTMOST-2D Fast Radio Bursts

We request the use of the MWA rapid-response mode to perform triggered VCS observations onfast radio bursts (FRBs) detected by the recently-upgraded UTMOST-2D radio telescope. Theorigin of FRBs remains a mystery, and there is debate as to whether there are two different FRBpopulations; repeaters and non-repeaters. While the majority of bursts have been detected around~1GHz, there are now reported detections (from a repeating FRB) with LOFAR between110-188 MHz. Observations of FRBs at low frequencies are important as they allow us to place constraints on the circumburst medium and help us to understand the FRB emission mechanism. For example, is the lack of low frequency (<300 MHz) FRB detections due to free-free absorption or is it a clue about the burst physics? Could FRBs be broadband or do we expect a single emitter to produce signals that have an individually narrow band-width but occurring over the entire radio frequency range? To perform FRB searches with the MWA, the high time resolution of the VCS mode is required to detect these narrow-band (ms) signals. However, blind searches are not viable for the MWA VCS due to the high data collection rate, and a dedispersion search on this data volume is not computationally feasible. Instead, we propose to perform triggered VCS observations from FRBs detected with UTMOST-2D. For a typical FRB DM range of 300-3000 pc cm^-3, the response time of UTMOST-2D transmitting an alert and MWA repointing is less than the expected dispersion delay between the observing frequencies of the two telescopes. Taking into account this delay along with the expected dispersion sweep across the MWA band, we only require 5 minutes of VCS data capture per trigger to search for a signal via incoherent and coherent beam-forming at the FRB position provided by UTMOST-2D.TransientsY00.17 (10 minutes)
Bhat (1)

Commissioning the Voltage Dump Mode of MWAX for triggering on ASKAP FRB detections

We propose to undertake science commissioning of the voltage dump functionality of the MWAXVCS, in response to external triggers from other facilities such as ASKAP, and to gear up the MWA for its continued exploitation for low-frequency triggering on FRBs. The FRB field has astonishingly flourished over the past half decade, with multiple significant breakthroughs including an explosion in their tally with CHIME coming online, and the first interferometric localisation with ASKAP. Measurements of their scattering, scintillation, polarisation and Faraday rotation properties are becoming routine, and theoretical efforts to understand their origin and progenitors continue unabated. With its large field of view (∼30deg2) and interferometric advantages, ASKAP has emerged as the front runner in the field, with 20+ FRBs localised to arcsecond precision. The MWA’s co-location at the Murchison site provides unique opportunities for undertaking efficient co-observing and triggering observations. Our shadowing campaigns in 2018-2019 yielded the most stringent constraints on the low-frequency emission from the class of non-repeating FRBs. In 2020, the focus shifted to the development and testing of voltage dump modes and strategies toward optimising them. Through this proposal we will interface, test and commission such a mode for the new high time resolution system, MWAX VCS. Simultaneous detection of even a single FRB would mean a huge payoff, and will further tighten the constraints on the spectral and scattering properties for the class of non-repeating FRBs, besides putting an end to the long-standing puzzle about an apparent lack of their emission at low frequencies. While this proposal is primarily focused on triggering in coordination with ASKAP, the capability we develop will also support other similar projects that are being conceived or considered, in coordination with FAST, UTMOST and CHIME, and is thus vital to support a broader range of transient projects with the MWA.TransientsY07.5  (+ engineering test time)
Bhat (2)

Advancing the science commissioning of new high-time resolution system MWAX VCS

We propose to carry forward the science commissioning efforts relating to MWAX VCS, the new high time resolution mode for the MWA. With the successful commissioning of the new tied-array beam-former, an important milestone has been reached toward ensuring the continuation of pulsar and fast transient science activities with the upgraded system. The main focus this semester will therefore be to make further progress through a series of science commissioning tasks that were outlined in our original submission (for the 2021 semester), including checking and verifying frequency accuracy and timing stability with the new system, and to undertake quality checks and careful assessments of array calibration and the sensitivity attained, with the eventual goal of delivering the full range of science capabilities that existed for the legacy VCS system. With the continuation of the SMART survey now deferred for 2022B,the focus this semester will be on the completion of commissioning exercise, which will also benefit the execution and timely completion of the SMART survey data project later this year. We will distribute the efforts to span across the semester, and prioritise to suit the LST range of targets and available resources. We have also suitably revised targets and expanded the commissioning exercise to include additional goal of commissioning MWAX VCS for the distributed channel setup (the so-called picket-fence mode)that are useful for precision measurements of dispersion and rotation measures. While the SMART project will indeed benefit from the full range of capabilities and functionalities that we will develop, test, validate and commission through this proposal, the overall exercise is critically important for ensuring continued science exploitation of the MWA for a range of pulsar and fast transient science work – an overarching goal of this project.PulsarsN06.5
Bhat (3)

Timing and imaging follow-up of the third pulsar discovered with the MWA

We request 5.5 hours of MWA time to undertake follow-up observations of PSR J1002−2036, the third pulsar to be discovered with the MWA from our ongoing Southern-sky MWA Rapid Two-metre(SMART) survey project. The pulsar has a rotation period of 1.677 s and a dispersion measure (DM)of 43.172pc cm−3. It was discovered in the ongoing first-pass processing, where we perform a shallow survey, reaching∼30% of the full-array sensitivity. To date,∼5% of the data have been searched (including candidate scrutiny) out to DMs∼250pc cm−3, limiting to basic periodicity (targeting primarily long-period pulsars). The pulsar’s detection in an another SMART observation provided an independent confirmation. Its non-detection in continuum imaging surveys, along with our detection significance(∼10-σin a 10-min observation) suggest that the pulsar is likely a low-luminosity object, akin to the first pulsar (PSR J0036−1033) discovered with the MWA. No archival data are available for useful follow-ups. We propose regular follow-up observations for timing and initial phase connection, and to determine the spin and astrometric parameters, including precise estimation of the spin period and its first derivative. We will also use these data to undertake one of the commissioning goals for MWAX VCS, where we correlate and image for prospective pulsar detection in imaging and for candidate identification to aid pulsar searching efforts. The observations will be distributed into multiple ∼30-minute sessions to make optimal use of available VCS resources and to ensure a logarithmic cadence that is required for phase connection. We request a majority of the time be scheduled in the month of April when the pulsar will still be a nightly object, followed by monthly observations for the remainder of the semester. We will promptly process the data, given our intent to report this discovery in an upcoming publication.PulsarsN05.5

MWA Follow-up of Neutrino Transient Candidates

We request MWA follow-up of neutrino transient candidates detected by the IceCube neutrino telescope. These follow-up observations will either lead to the strongest limits to date on prompt radio emission from neutrino transients, or to the detection of a correlated radio signal. The latter will lead to the localization of the astrophysical sources that emit high-energy neutrinos. In addition, the combined particle and radio detection from a common astrophysical source will contribute to evidence for the origin of cosmic rays. For around 40% of the IceCube neutrino alerts, the source is expected to be visible immediately from the MWA site. We expect to receive and follow up of order two neutrino triggers during 2022-A. The follow-up observations would be disruptive target of opportunity observations. We request 30 minutes of prompt follow-up of each trigger, followed by a second epoch 1–2 weeks later for each trigger (matched in LST range) for comparison.TransientsY30
Hurley-Walker (1)

Monitoring the Galactic Plane for minute-timescale radio transients

Using data from the GaLactic and Extragalactic All-sky MWA eXtended (GLEAM-X)survey, Hurley-Walker et al. 2022 have detected a bright, highly polarised radio transient, with an extremely unusual periodicity of 18.18 minutes. It was switched on for the period of January 2018 to March 2018 inclusive, and despite an exhaustive search, and follow-up DDT with MWA and other telescopes in 2021, we have been unable to find detections outside of this interval. We hypothesise that this transient is part of a heretofore undiscovered population, and propose a monitoring campaign that takes advantage of the MWA’s wide field-of-view and sensitivity to low frequencies to detect more of these objects in near real time, enabling rapid follow-up and better understanding of their nature.TransientsN130 (+ up to 100 follow-up)0 (+ up to 100 follow-up)

Hurley-Walker (2)

GaLactic and Extragalactic All-Sky MWA-eXtended (GLEAM-X) survey

The aim of the GaLactic and Extragalactic All-sky MWA eXtended (GLEAM-X) survey is to create a legacy dataset for innovative low-frequency science which will serve many astronomers over coming years. A deeper all-sky survey at higher resolution will enable a legion of science capabilities, whilst maintaining advantages over LOFAR including larger field-of-view (and survey speed), wider frequency coverage (72—231 MHz ), and better sensitivity to extended emission. We continue the successful snapshot imaging and image-plane combination strategy of GLEAM, and ionospheric triage methods we have developed for GLEAM-X. Based on our results so far, GLEAM-X will have lower noise, higher surface brightness sensitivity, and possess the critical wide bandwidth that sets it apart from complementary surveys such as TGSS. These properties will enable a wide range of continuum science(see Science Justification), and the data are designed to be commensally used for transients science. This wide-area survey will be most useful with uniform, complete sky coverage. We have examined further data taken for GLEAM-X and determined which nights cannot be imaged deeply due to highly active ionospheric weather. We request re-observations of these nights in order to complete our sky coverage.GEGN2520

Pilot study to image lightning in high time and spatial resolution

Lightning is a form of dielectric breakdown of the air, the most powerful emitter of Very High Frequency (VHF) radio waves occurring naturally on Earth. However, the physical mechanisms by which lightning initiates in the atmosphere remain poorly understood, despite centuries of research. Setting up dedicated observatories for studying this phenomenon is challenging, requiring both large bandwidths and sufficiently fine time and spatial resolutions in order to accurately map the progress of lightning discharges through the atmosphere. However, these requirements can be met by latest-generation radio telescopes, as has been recently demonstrated by both the Low Frequency Array (LOFAR) and the Long Wavelength Array (LWA). The MWA in its extended configuration is an ideal instrument for carrying out such studies. Its newly commissioned MWAX Voltage Capture System (VCS), coupled with the inversion of the coarse PFB is capable of probing incident emission on nanosecond timescales, while its 5 km baselines provide the necessary spatial resolution for a full three-dimensional reconstruction of lightning strikes. The resulting “movies” will enable detailed studies of lightning discharge mechanisms as they occur in nature. We therefore propose a pilot study to demonstrate the MWA’s capability for rapid imaging of lightning dis-charges in the atmosphere, opening up new vistas for MWA science. Other significant outcomes for this project include synergy with existing projects (e.g. cosmic ray research), as well as new opportunities for MWA outreach and industry engagement.High time-resolution: lightningY05

Monitoring of X-ray binary transient outbursts with the MWA

We propose pointed MWA observations of any nearby, bright (≳50 mJy) outbursting X-ray binary(XRB) during the 2022–A observing semester. The low-frequency behaviour of radio jets in XRBs is still not well constrained, especially at frequencies<500 MHz. XRBs can produce two different types of radio jets over the course of a single outburst. Optically thick, flat-spectrum, compact steady jets are observed during the hard state, whereas steep-spectrum, relativistically-moving transient jets are detected near the peak of the outburst, when the source undergoes a transition from the hard to the soft X-ray spectral state. Our previous monitoring of XRB jets with the MWA has detected both types of jets, and ascertained their physical parameters. However, deeper, higher-cadence observations would address several unresolved questions. For compact jets, we aim to acquire high-sensitivity broadband spectra to determine whether there is any low-frequency break, which has not previously been detected but would provide information on the spatial extent of the jet (Malzac 2014).For transient jets, multiple broadband observations (MHz to GHz) over the course of a full outburst, coupled to VLBI monitoring to determine the source expansion, would allow us to characterise the evolution of the magnetic field strength as the jets evolved and expanded. Our previous study was limited to a single such spectrum, and better time coverage would show how the magnetic field strength, the minimum energy and the structure of the transient jet knot evolve as it propagates downstream.TransientsY300

An Interplanetary Scintillation Survey with the extended Phase II MWA

We propose to conduct daily observations of Interplanetary Scintillation (IPS). We can use these observations for both space weather monitoring, and for determining the arcsecond-scale structure of the detected sources. With 8⨉10 minute observations per day we can cover all solar elongations where we can make optimum IPS measurements, following the survey methodology used in 2019A and 2020A/B. Following our practise in 2020B, we wish to continue to intersperse our standard (81MHz and 162MHz) frequency with observations at 215MHz (1⨉10 minute observation per day) as this provides extremely valuable information on Galactic scatter broadening, as well as spectral information on the compact components). Aside from that (and a few observations in September which will allow access to fields that were not successfully observed in previous years), the main focus of these observations will be for space weather analysis. A large number of significant events in early 2022 mean it is likely that the Sun will be active through much of 2022A. We also have a new PhD student who has already written an IPS data reduction pipeline, and the aim is that much of this data will processed in a much more timely fashion than in previous years. In contrast to most other projects using the long-baseline MWA, IPS is not strongly affected by bandwidth smearing and we can accept 40kHz frequency resolution, reducing the archive volume of our observations by a factor of 4.SHIN274.60

MWA Observations of the Sun

A hundred hours of observing time for solar observations is requested during the 2022-Aobserving semester. These data will be used to address science objectives for solar burst science (Goal A); studies of weak non-thermal radiation (Goal B); quiet sun science (Goal C), imaging of CME plasma (Goal D) and observations coordinated with various spacecraft and the updated GMRT (Goals E and F). Goal A will focus on detailed investigations of individual events seen in the MWA data, using the unsurpassed spectroscopic snapshot imaging ability of the MWA to address some key solar physics questions. Detailed observations of type II bursts and type III bursts will be one focus. Goal B will address studies of the numerous short lived and narrow band emission features, significantly weaker than those seen by most other instruments revealed by the MWA. These emission features do not resemble any known types of solar bursts, but are possible radio signatures of the “nanoflares' which have long been suspected to play a role in coronal heating. A large database of these events is needed to be able explore this possibility and to reliably estimate their contribution to coronal heating. These observations will contribute to this database. Goal C will focus on characterising the Sun’s background thermal emissions, their short and long term variability and look for evidence of a scattering disc around the Sun. Goal D makes use of our high dynamic range capability to directly image the gyrosynchrotron emission from the CME plasma. Goal E proposes opportunistic coordinated observations with the Parker Solar Probe, the Solar Orbiter and the Chandrayaan-2. Goal F proposes coordinated observations with the upgraded GMRT to verify unexpected presence of linear polarization in some active solar emissions observed using the MWA.SHIN1000

A low-frequency hunt for the diffuse radio halo in Abell 3667

Merging galaxy clusters are highly complex and dynamically active physical systems that play host to a broad range of rich physical processes such as shocks and turbulence. These processes mediate the deposition of gravitational potential energy into the magnetised thermal plasma that makes up the bulk of the baryonic matter content of a cluster, and can give rise to spectacular non-thermal phenomena: large-scale diffuse radio sources. However, the details of the mechanisms responsible for the generation of these sources, the canonical radio relics and haloes, are poorly understood; to truly unlock the secrets of particle acceleration in the intracluster medium (ICM), we require deep observations across a broad radio frequency range, combined with X-ray and optical data. We are proposing deep low-frequency observations of the galaxy cluster Abell 3667 with the MWA across the 72 – 300 MHz frequency range. This cluster is the prototypical merging cluster in the southern sky, and is known to host a pair of spectacular radio relics either side of the cluster centre, as well as an ultra-faint radio halo that has recently been detected for the first time using mid-frequency data from the MeerKAT telescope in South Africa. Our new observations will allow us to map the spectral index of the radio halo for the first time, as well as studying the spectral index profile of the radio relics at higher sensitivity and resolution than ever before at these frequencies. We will use state-of-the-art techniques to unlock the complex physics of turbulent acceleration in the ICM (which generates the radio halo) and diffusive shock acceleration (DSA; which powers the radio relics). We emphasise the game-changing nature of our deep observations, which will have the sensitivity and resolution to revolutionise our understanding of this spectacular and nearby cluster merger.GEGN31 (+ calibrators)0

Measuring Variable Optical Depths with Spectral Variability

Gigahertz-peaked spectrum (GPS) radio sources are a unique subset of active galactic nuclei (AGN) which can display compact, double-lobe morphology. GPS sources are identified by a spectral peak in their radio spectral energy distributions(SED) in the gigahertz regime, typically have sizes of 1−20 kpc, and show little to no polarisation or variability. Compact radio galaxies can also peak at MHz frequencies (often referred to as Megahertz-peaked spectrum (MPS) sources) we refer collectively to all sources displaying a peak in their SED as peaked spectrum sources (PSS), regardless of peak frequency. PSS have played a pivotal role in shaping our understanding evolutionary paths of radio galaxies as they are hypothesised to be the progenitors to massive, radio-loud AGN (O’Dea, 1998). In 2020, we performed roughly simultaneous observations with the MWA and the ATCA to obtain broad-band spectra for 15 different PSS with 8 different epoch in order to study the spectral variability. All 15 PSS were previously identified as variable in our earlier survey using the GaLactic and Extragalactic All-sky MWA Survey (GLEAM; Hurley-Walker et al., 2017; Wayth et al., 2015). In this study, we identified several different types of variability at MHz frequencies but no long term GHz variability. Furthermore, we were able to attribute the variability for several sources to intrinsic physical properties including variations in the optical depth and an expanding ejection travelling away from the central AGN. To follow up, we have proposed for short timescale observations (hours to days) with the ATCA(Apr22 semester) to characterise the interstellar scintillation. We propose continued monitoring of these 15 PSS targets on a monthly time cadence to further constrain the intrinsic variability and determine the physical properties of the PSS. We request 6 epochs of observations with the MWA roughly separated by a month.GEGN750

Lensing magnification of the EoR 21cm signal by massive cluster: foreground modelling with extended array

Measuring the high redshift 21cm signal of neutral hydrogen during the Cosmic Dawn (CD) and Epoch of Reionization (EoR) is on e of the principle science goals of the Murchison Widefield Array (MWA). A major challenge preventing the detection is the presence of the overwhelming foreground contamination from the diffused Galactic emissions and extragalactic sources, which are at least four orders of magnitude brighter than the expected 21cm signal. The success of the signal detection relies on robust foreground removal, which has been extensively explored over the past decade. However, there is a significant uncertainty in providing signal estimates with regard to foreground residuals and signal loss from cleaning procedure. 

Instead of developing more complicated and efficient foreground-cleaning methods, it is promising to detect the 21cm signal that has been enhanced by the strong gravitational lensing of the galaxy clusters. Our simulation shows that the faint 21cm signal can be magnified by about 1-3 orders of magnitude in both power spectrum and imaging of the ionization structure of the IGM during EoR. Moreover, this method has a unique advantage in that it can only enhance the 21cm signal but not the Galactic emission, which is dominated foreground.

Here we propose an MWA-HFF project to detect the EoR 21cm signal with a magnification map generated by the strong gravitational lensing of massive clusters. In particular, we will focus on Abell S1063 in the HFFs with the consistent magnification maps from eight teams. In the current extended configuration, we will build the foreground model of this field for detecting the magnified 21cm signal in the forthcoming compact configuration.


Commissioning the commensal FRB search pipeline using the MWAX real-time beamformer 

This proposal will undertake the science commissioning of the real-time FRB search pipeline using the real-time incoherent beamformer implemented in the new MWA correlator (MWAX). In the last few years, the FRB field witnessed significant breakthroughs resulting from significant efforts of groups around the world. The interferometric localisations of several FRBs detected at GHz frequencies by the ASKAP CRAFT group enabled localisations of host galaxies and redshift measurements, which confirmed their extra-galactic origin. At lower frequencies, the CHIME telescope detected large sample of repeating and non-repeating FRBs at frequencies between 400 – 800 MHz, which enabled studies of physical properties of these two, apparently different, populations. Many CHIME FRBs were detected down to 400 MHz, which is only 100 MHz higher than highest observing frequencies of the MWA. Moreover, CHIME repeating FRBs were observed by LOFAR and one of them (FRB 20180916B) was indeed detected down to 110 MHz resulting in the first ever FRB detections below 300 MHz. The LOFAR observations, coordinated with the APERTIF radio telescope operating at GHz frequencies, showed that the low-frequency bursts are typically observed at different epochs than the high frequency signals. Hence, besides on-going efforts to detect low-frequency counterparts of ASKAP FRBs by triggering and shadowing ASKAP with the MWA (Sokolowski et al., 2018 and project G0034), it is also important to develop an autonomous real-time FRB detection capability and perform complementary real-time FRB searches with the MWA and other low-frequency instruments at the MRO. These kinds of developments will enable independent discoveries of FRBs without reliance on external triggers. Although sensitivity to FRBs in the incoherent mode is reduced by about a factor of≈11, our estimations based on the current FRB rates at these frequencies show that it should be possible to detect at least several FRBs per year assuming continuous sky observations. Nevertheless, even non-detections will firmly establish FRB rates at frequencies below 300 MHz, which are currently highly uncertain. Furthermore, the goal of the project is to develop the commensal observing mode and perform these kinds of searches during all types.High time-resolution: FRBsN20 (+ engineering test time)0

Rapid-response MWA observations of Swift gamma-ray bursts

We request the use of the MWA rapid-response mode to perform triggered VCS observations of Swift gamma-ray bursts (GRBs) during the 2022A semester. The prompt and early-time radio emission associated with GRBs is still a poorly explored regime, particularly at MHz frequencies. There are two main classes of GRBs: short and long. Short GRBs (SGRBs) are linked with binary neutron star (BNS)mergers and predicted to produce prompt, coherent emission (such as fast radio bursts, FRBs; Totani,2013; Falcke & Rezzolla, 2014; Zhang, 2014), the detection of which would allow us to distinguish between different binary merger models and scenarios. Long GRBs (LGRBs) are linked with core-collapse supernovae, and could also generate low-frequency prompt radio emission (Katz, 2016;Falcke & Rezzolla, 2014), though it remains unclear whether this emission can escape from the local environment (Zhang, 2014). As prompt radio emission becomes delayed with decreasing frequency due to dispersion, such signals associated with GRBs may not arrive for seconds up to several minutes following the initial burst alerts at MWA frequencies. Given that the MWA rapid-response mode can automatically repoint the telescope within 20 seconds of receiving an alert, MWA is uniquely capable of being on-target in time to observe the earliest prompt emission. The MWA VCS observation with its high temporal resolution is most suitable for searching for the prompt radio emission associated with GRBs. We focus on Swift alerts, which, unlike Fermi alerts, provide ~arcsec localisations for GRBs. This enables us to localise the GRB to within a synthesised beam of MWA and coherently beamform the VCS data, which can maximize our sensitivity. Even with non-detection, such rapid-response MWA VCS observations have the sensitivities necessary to rule out some GRB models, which will in-turn constrain different neutron star equation-of-state models. These experiments also directly test transient strategies for SKA-Low.TransientsY02
XuSearching for the repeating FRBs at low radio frequenciesSince the first discovered FRB, about six hundred sources have been detected. The majority of the FRBs are observed not to repeat. However, the discovery of FRB 121102 revealed that at least a subset of FRBs exhibit a repeating nature. Recently LOFAR reported the detection of the repeater FRB 20180916B at 110-188MHz, by far the lowest-frequency detections of any FRB to date. We expect synergy MWA and FAST observations to detect repeating FRBs below 110 MHz and compare the low-frequency properties with other frequencies. In addition, we will use Machine Learning methods to process the data to increase the chance of detecting weak FRBs.TransientsN04
X. Zhang

Monitoring a quadruple M dwarf system for minute-timescale radio flares

Using data from the GaLactic and Extragalactic All-sky MWA eXtended (GLEAM-X) survey, Zhang et al. have detected a highly polarised radio transient. This transient was on for 40 minutes in October 2020; after an in-depth search within the MWA archival data, no further detection was made besides this interval. A follow-up observation using ATCA revealed polarised emission at 2 GHz from the source. The transient is located within 10 arcsec of a known quadruple M dwarf system and is therefore catagorised as a flaring star detected by the MWA. We propose a monitoring campaign to detect more flares, investigate the flare rates, confirm the origin of the flare and the emission mechanism.TransientsN400

Observation of spectral turnover pulsar J0738-4042 in Gum nebula 

The turnover of the pulsar spectral index is still no good explanation. Using data from the GaLactic and Extragalactic All-sky MWA eXtended (GLEAM-X) survey, we crossed match the sources, then found a source PSR J0738-4042 spectral index with turnover at low radio frequencies. Turnover may be caused by some kind of absorption in the magnetosphere, loss of efficiency of the emission mechanism, or interstellar effects. The physical mechanism usual explanation for turnover is synchronous-self-absorption (SSA), free-free absorption (FFA), or superimpose. Polarimetric studies of pulsars at low radio frequencies provide important observational perspectives into the pulsar emission mechanism and probe the properties of the magneto-ionic interstellar medium (ISM). High sensitivity observations of pulsars at low radio frequencies are ideal to use both effects and their variation with time and frequency to study the properties of the ISM itself. PSR J0738-4042 is close to the center in Gum nebula which is an extending emission nebula, so the pulsar has a very complex interstellar environment. Therefore, the low-frequency observation of PSR J0738-4042 will help us to study the interstellar absorption near the Gum nebula and clarify the absorption mechanism of the pulsar spectral turnover phenomenon. The shape of a scattered profile and its evolution as a function of frequency give us insights into the underlying geometry, dynamics, and physics of the ISM.High time-resolution: pulsarsN01.5
Z. Zhang

A Pioneer Search of Pulsars in Low Frequency in Globular Clusters

With old stellar environment and extraordinarily high stellar encounter rates, globular clusters (GCs) are ideal regions for the search and study of millisecond pulsars (MSPs). So far, more than 90% of 236 pulsars observed in 36 GCs are MSPs. However, despite of the theoretically steep spectra of MSPs, the lowest frequency of them ever been found in GCs is still as high as 327 MHz. This is probably due to the pulsar signals being smeared out by scattering, or the possible flattening of the pulsar spectra in low-frequency bands. With the high sensitivity of MWA among low-frequency radio arrays, there is a great chance to cross this barrier, to find the first pulsar below 300 MHz among several GC candidates in the MWA field-of-view (FoV). As a first attempt, we propose to take a 1.5 hrs observation, pointed to a region covering two important GCs (NGC 6624 and NGC 6626) simultaneously. We choose a high MWA frequency band of 200.32 - 231.04 MHz (channel no. 157 - 180) to reduce the scattering effect. These two targets both harbour more than 10 known pulsars, with the brightest ones (namely J1824-2452A and B1820-30A) highly possible to be detected in this observation. After proving feasibility, this observation can bring brand new examples to study low-frequency behaviors of pulsars in GCs, to help improving our understanding of GCs, such as the roles they play in the evolution of galaxies.High time-resolution: pulsarsN01.5


*Student PI;  †Open Access proposal

Director's Discretionary Time (DDT) Observations


Visibility Time Requested


VCS Time Requested


Steven Tingay2022-02-15Chang'e 5-T1 rocket booster colliding with the Moon3.3
Steven Tingay2022-06-30Search for missing cube-sat0.25
Steve Prabu2022-03-31Observations for Space Situational Awareness1.2
Steve Prabu2022-07-26Observations for Space Situational Awareness0.5
Steve Prabu2022-09-30Observations for Space Situational Awareness0.1
Natasha Hurley-Walker2022-01-17Follow-up observations of a transient found by the GLEAM-X survey3.7
Ting Yu2022AObservation of spectral turnover pulsar J0738-4042 in Gum nebula
Manisha Caleb2022-03-09Low frequency observations of PSR J0901−4046
Natasha Hurley-Walker2022-06-13Follow-up observations of another transient found by the GLEAM-X survey6
Natasha Hurley-Walker2022-09-13Star-Planet Interaction in the Nearby AU Microscopic Exoplanet System9
Randall Wayth2022-08-18Simultaneous MWA/EDA2 observations for an m-mode all-sky image with 0.1 degree resolution24
Himanshu Tiwari2022-09-15Observations of the same field with, and without, the Moon present in the field.30.7
Natasha Hurley-Walker2022-10-28Follow-up observations of a new long period transient12
Divya Oberoi2022-11-15Solar observations10