ORCID Profile
0000-0001-9550-628X
Current Organisation
Curtin University
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Publisher: Oxford University Press (OUP)
Date: 30-05-2022
Abstract: We present a low-frequency (170–200 MHz) search for prompt radio emission associated with the long GRB 210419A using the rapid-response mode of the Murchison Widefield Array (MWA), triggering observations with the Voltage Capture System for the first time. The MWA began observing GRB 210419A within 89 s of its detection by Swift, enabling us to capture any dispersion delayed signal emitted by this gamma-ray burst (GRB) for a typical range of redshifts. We conducted a standard single pulse search with a temporal and spectral resolution of $100\\, \\mu$s and 10 kHz over a broad range of dispersion measures from 1 to $5000\\, \\text{pc}\\, \\text{cm}^{-3}$, but none were detected. However, fluence upper limits of 77–224 Jy ms derived over a pulse width of 0.5–10 ms and a redshift of 0.6 & z & 4 are some of the most stringent at low radio frequencies. We compared these fluence limits to the GRB jet–interstellar medium interaction model, placing constraints on the fraction of magnetic energy (ϵB ≲ [0.05–0.1]). We also searched for signals during the X-ray flaring activity of GRB 210419A on minute time-scales in the image domain and found no emission, resulting in an intensity upper limit of $0.57\\, \\text{Jy}\\, \\text{beam}^{-1}$, corresponding to a constraint of ϵB ≲ 10−3. Our non-detection could imply that GRB 210419A was at a high redshift, there was not enough magnetic energy for low-frequency emission, or the radio waves did not escape from the GRB environment.
Publisher: BMJ
Date: 07-2019
DOI: 10.1136/BMJOPEN-2019-030836
Abstract: Suicide rates in India are among the highest in the world, equating to over 200 000 suicides annually. Reports of suicides are a routine feature in major newspapers in India, and reporters may selectively present ‘newsworthy’ suicide stories. The aim of this paper was to systematically investigate whether mass media reports of suicides reflect the epidemiological data on suicide in a high suicide state in India. We undertook a content analysis study to extract sociodemographic data on suicides reported among nine of the most highly read daily newspapers in the high suicide southern state of Tamil Nadu between June and December 2016. A total of 1258 newspaper articles were retrieved containing reports on 1631 suicides. Two-tailed binomial tests on aggregate frequencies assessed whether the sociodemographic characteristics of suicides in the newspaper articles were different to the population suicide statistics for Tamil Nadu. We identified some statistically significant discrepancies between suicide characteristics in the population and the media. Suicides involving females (p .001), those aged under 30 years (p .001), separated or widowed males (p .001), unmarried females (p .001), those using methods with a higher case fatality rate (ie, hanging (p .001), jumping off high structures (p .001) and coming under vehicles (p .001) and those who were students (p .001) or working in the agricultural sector (p .001) were significantly over-reported relative to their occurrence in the broader population. Suicides involving men (p .001), those aged over 30 years and above (p .001), those who were married and suicides by poisoning (p .001) were significantly under-reported relative to their occurrence in the broader population. The suicide characteristics in the print media were not entirely representative of suicides in the broader Tamil Nadu population, which may lead the general public to develop misunderstandings about suicide in their state. The discrepancies we identified will inform tailored suicide prevention education for media professionals.
Publisher: Oxford University Press (OUP)
Date: 15-09-2020
Abstract: Aiming to fill a crucial gap in our observational knowledge of the early Universe, experiments around the world continue to attempt to verify the claimed detection of the redshifted 21-cm signal from Cosmic Dawn by the EDGES experiment. This sky-averaged or ‘global’ signal from neutral hydrogen should be detectable at low radio frequencies (50–200 MHz), but is difficult to measure due to bright foreground emission and difficulties in reaching the required levels of instrumental-calibration precision. In this paper, we outline our progress toward using a novel new method to measure the global redshifted 21-cm signal. Motivated by the need to use alternative methods with very different systematic errors to EDGES for an independent result, we employ an array of closely spaced antennas to measure the global-sky signal interferometrically, rather than using the conventional approach with a single antenna. We use simulations to demonstrate our newly developed methods and show that, for an idealized instrument, a 21-cm signal could theoretically be extracted from the visibilities of an array of closely spaced dipoles. We verify that our signal-extraction methods work on real data using observations made with a Square-Kilometre-Array-like prototype, the Engineering Development Array-2. Finally, we use the lessons learned in both our simulations and observations to lay out a clear plan for future work, which will ultimately lead to a new global redshifted 21-cm instrument: the All-Sky SignAl Short-Spacing INterferometer (ASSASSIN).
Publisher: American Astronomical Society
Date: 06-12-2017
Publisher: American Astronomical Society
Date: 04-2021
Abstract: We report the discovery of the first new pulsar with the Murchison Widefield Array (MWA), PSR J0036−1033, a long-period (0.9 s) nonrecycled pulsar with a dispersion measure (DM) of 23.1 pc cm −3 . It was found after processing only a small fraction (∼1%) of data from an ongoing all-sky pulsar survey. Follow-up observations have been made with the MWA, the upgraded Giant Metrewave Radio Telescope (uGMRT), and the Parkes 64 m telescopes, spanning a frequency range from ∼150 MHz to 4 GHz. The pulsar is faint, with an estimated flux density ( S ) of ∼1 mJy at 400 MHz and a spectrum , where ν is frequency. The DM-derived distance implies that it is also a low-luminosity source (∼0.1 mJy kpc 2 at 1400 MHz). The analysis of archival MWA observations reveals that the pulsar’s mean flux density varies by up to a factor of ∼5–6 on timescales of several weeks to months. By combining MWA and uGMRT data, the pulsar position was determined to arcsecond precision. We also report on polarization properties detected in the MWA and Parkes bands. The pulsar’s nondetection in previous pulsar and continuum imaging surveys, the observed high variability, and its detection in a small fraction of the survey data searched to date, all hint at a larger population of pulsars that await discovery in the southern hemisphere, with the MWA and the future low-frequency Square Kilometre Array.
Publisher: Springer Science and Business Media LLC
Date: 15-06-2020
DOI: 10.1186/S12888-020-02715-9
Abstract: Debunking suicide myths, such as ‘asking someone about suicide could make them start thinking about it’ is a common strategy in suicide prevention education. However, there has been little research investigating the relationship between suicide myths and helping behavior toward people at risk of suicide. We aimed to identify sociodemographic characteristics associated with belief in eight common suicide myths and the associations between beliefs in these myths and helping intentions and behaviors toward a family member or friend in severe distress or at risk of suicide. We conducted a random digit dial (mobile and landline) survey of 3002 Australian adults. We asked respondents about their beliefs in suicide myths, intentions to help a person in severe distress or at risk of suicide presented in a vignette, and helping actions taken toward such a person in the last 12 months. We weighted this data to be representative of the Australian population. Regression analyses were undertaken to determine associations between sociodemographic and exposure characteristics and beliefs in suicide myths, and between beliefs in myths and helping intentions and behaviors. Being male, speaking a language other than English at home and being over 60 years were associated with the strongest beliefs in suicide myths. The strongest and most consistent associations were found between belief in the myth ‘asking someone about suicide could make them start thinking about it’, risk assessment intentions and behaviours and intentions to undertaken actions not recommended for suicide prevention. Identifying those sociodemographic groups most likely to believe in suicide myths allows targeted intervention for suicide prevention education ‘debunking’ suicide myths. By isolating those myths that are most commonly believed, and their specific effects on helping intentions and behaviors, suicide prevention educators can target these specific myths to have the most effect on helping behavior. Our findings suggest that targeting the myth ‘asking someone about suicide could make them start thinking about it’ may have the greatest effects on helping behavior, and that men, those aged over 60 years and those speaking a language other than English at home could most benefit from myth ‘debunking’.
Publisher: Cambridge University Press (CUP)
Date: 2019
DOI: 10.1017/PASA.2019.41
Abstract: The Murchison Widefield Array (MWA) is an open access telescope dedicated to studying the low-frequency (80–300 MHz) southern sky. Since beginning operations in mid-2013, the MWA has opened a new observational window in the southern hemisphere enabling many science areas. The driving science objectives of the original design were to observe 21 cm radiation from the Epoch of Reionisation (EoR), explore the radio time domain, perform Galactic and extragalactic surveys, and monitor solar, heliospheric, and ionospheric phenomena. All together $60+$ programs recorded 20 000 h producing 146 papers to date. In 2016, the telescope underwent a major upgrade resulting in alternating compact and extended configurations. Other upgrades, including digital back-ends and a rapid-response triggering system, have been developed since the original array was commissioned. In this paper, we review the major results from the prior operation of the MWA and then discuss the new science paths enabled by the improved capabilities. We group these science opportunities by the four original science themes but also include ideas for directions outside these categories.
Publisher: Elsevier BV
Date: 07-2021
Publisher: Oxford University Press (OUP)
Date: 06-09-2018
Publisher: Wiley
Date: 12-01-2021
DOI: 10.1002/WPS.20832
Publisher: Hogrefe Publishing Group
Date: 07-2017
DOI: 10.1027/0227-5910/A000444
Abstract: Abstract. Background: Since the mid-1990s concerns have been raised regarding the possible links between suicide and the Internet, especially among adolescents and young adults. Aims: To identify the nature and extent of the scientific publications, especially original research studies, on suicide and the Internet, and to investigate how the field has developed over time. In particular, this mapping study looks at types of publications, topic areas, focus of original research papers, and suicide-related variables of interest in publications. Method: A search of three major databases (PubMED, PsycINFO, and Sociological Abstracts) was conducted to identify papers published until the end of January 2015. Results: The study identified 237 publications on suicide and the Internet published from 1997 to the end of January 2015. These included 122 original research papers. The three most frequent topic areas covered in publications were searching for information on suicide, online interventions, and online suicide-related behaviors. The online mediums most frequently studied were online forums/message boards, search engines, intervention and information websites, and social media. Limitations: The mapping study did not include an analysis of results of research studies and did not assess their quality. Conclusion: The field is rapidly evolving, as seen in the recent increase in the number of publications. However, there are gaps in terms of the countries where research is conducted and the coverage of topics.
Publisher: Cambridge University Press (CUP)
Date: 2020
DOI: 10.1017/PASA.2020.4
Publisher: Elsevier BV
Date: 02-2022
Publisher: Cambridge University Press (CUP)
Date: 2021
DOI: 10.1017/PASA.2021.38
Abstract: We present a broadband radio study of the transient jets ejected from the black hole candidate X-ray binary MAXI J1535–571, which underwent a prolonged outburst beginning on 2017 September 2. We monitored MAXI J1535–571 with the Murchison Widefield Array (MWA) at frequencies from 119 to 186 MHz over six epochs from 2017 September 20 to 2017 October 14. The source was quasi-simultaneously observed over the frequency range 0.84–19 GHz by UTMOST (the Upgraded Molonglo Observatory Synthesis Telescope) the Australian Square Kilometre Array Pathfinder (ASKAP), the Australia Telescope Compact Array (ATCA), and the Australian Long Baseline Array (LBA). Using the LBA observations from 2017 September 23, we measured the source size to be $34\\pm1$ mas. During the brightest radio flare on 2017 September 21, the source was detected down to 119 MHz by the MWA, and the radio spectrum indicates a turnover between 250 and 500 MHz, which is most likely due to synchrotron self-absorption (SSA). By fitting the radio spectrum with a SSA model and using the LBA size measurement, we determined various physical parameters of the jet knot (identified in ATCA data), including the jet opening angle ( $\\phi_{\\rm op} = 4.5\\pm1.2^{\\circ}$ ) and the magnetic field strength ( $B_{\\rm s} = 104^{+80}_{-78}$ mG). Our fitted magnetic field strength agrees reasonably well with that inferred from the standard equipartition approach, suggesting the jet knot to be close to equipartition. Our study highlights the capabilities of the Australian suite of radio telescopes to jointly probe radio jets in black hole X-ray binaries via simultaneous observations over a broad frequency range, and with differing angular resolutions. This suite allows us to determine the physical properties of X-ray binary jets. Finally, our study emphasises the potential contributions that can be made by the low-frequency part of the Square Kilometre Array (SKA-Low) in the study of black hole X-ray binaries.
Publisher: Cambridge University Press (CUP)
Date: 2023
DOI: 10.1017/PASA.2023.18
Abstract: In Paper I, we presented an overview of the Southern-sky MWA Rapid Two-metre (SMART) survey, including the survey design and search pipeline. While the combination of MWA’s large field-of-view and the voltage capture system brings a survey speed of ${\\sim} 450\\, {\\textrm{deg}}^{2}\\,\\textrm{h}^{-1}$ , the progression of the survey relies on the availability of compact configuration of the Phase II array. Over the past few years, by taking advantage of multiple windows of opportunity when the compact configuration was available, we have advanced the survey to 75% of the planned sky coverage. To date, about 10% of the data collected thus far have been processed for a first-pass search, where 10 min of observation is processed for dispersion measures out to 250 ${\\textrm{pc cm}}^{-3}$ , to realise a shallow survey that is largely sensitive to long-period pulsars. The ongoing analysis has led to two new pulsar discoveries, as well as an independent discovery and a rediscovery of a previously incorrectly characterised pulsar, all from ${\\sim} 3\\% $ of the data for which candidate scrutiny is completed. In this sequel to Paper I, we describe the strategies for further detailed follow-up including improved sky localisation and convergence to timing solution, and illustrate them using ex le pulsar discoveries. The processing has also led to re-detection of 120 pulsars in the SMART observing band, bringing the total number of pulsars detected to date with the MWA to 180, and these are used to assess the search sensitivity of current processing pipelines. The planned second-pass (deep survey) processing is expected to yield a three-fold increase in sensitivity for long-period pulsars, and a substantial improvement to millisecond pulsars by adopting optimal de-dispersion plans. The SMART survey will complement the highly successful Parkes High Time Resolution Universe survey at 1.2–1.5 GHz, and inform future large survey efforts such as those planned with the low-frequency Square Kilometre Array (SKA-Low).
Publisher: Cambridge University Press (CUP)
Date: 2019
DOI: 10.1017/PASA.2021.58
Abstract: Many short gamma-ray bursts (GRBs) originate from binary neutron star mergers, and there are several theories that predict the production of coherent, prompt radio signals either prior, during, or shortly following the merger, as well as persistent pulsar-like emission from the spin-down of a magnetar remnant. Here we present a low frequency (170–200 MHz) search for coherent radio emission associated with nine short GRBs detected by the Swift and/or Fermi satellites using the Murchison Widefield Array (MWA) rapid-response observing mode. The MWA began observing these events within 30–60 s of their high-energy detection, enabling us to capture any dispersion delayed signals emitted by short GRBs for a typical range of redshifts. We conducted transient searches at the GRB positions on timescales of 5 s, 30 s, and 2 min, resulting in the most constraining flux density limits on any associated transient of 0.42, 0.29, and 0.084 Jy, respectively. We also searched for dispersed signals at a temporal and spectral resolution of 0.5 s and 1.28 MHz, but none were detected. However, the fluence limit of 80–100 Jy ms derived for GRB 190627A is the most stringent to date for a short GRB. Assuming the formation of a stable magnetar for this GRB, we compared the fluence and persistent emission limits to short GRB coherent emission models, placing constraints on key parameters including the radio emission efficiency of the nearly merged neutron stars ( $\\epsilon_r\\lesssim10^{-4}$ ), the fraction of magnetic energy in the GRB jet ( $\\epsilon_B\\lesssim2\\times10^{-4}$ ), and the radio emission efficiency of the magnetar remnant ( $\\epsilon_r\\lesssim10^{-3}$ ). Comparing the limits derived for our full GRB s le (along with those in the literature) to the same emission models, we demonstrate that our fluence limits only place weak constraints on the prompt emission predicted from the interaction between the relativistic GRB jet and the interstellar medium for a subset of magnetar parameters. However, the 30-min flux density limits were sensitive enough to theoretically detect the persistent radio emission from magnetar remnants up to a redshift of $z\\sim0.6$ . Our non-detection of this emission could imply that some GRBs in the s le were not genuinely short or did not result from a binary neutron star merger, the GRBs were at high redshifts, these mergers formed atypical magnetars, the radiation beams of the magnetar remnants were pointing away from Earth, or the majority did not form magnetars but rather collapse directly into black holes.
Publisher: Cambridge University Press (CUP)
Date: 2023
DOI: 10.1017/PASA.2023.17
Abstract: We present an overview of the Southern-sky MWA Rapid Two-metre (SMART) pulsar survey that exploits the Murchison Widefield Array’s large field of view and voltage-capture system to survey the sky south of 30 $^{\\circ}$ in declination for pulsars and fast transients in the 140–170 MHz band. The survey is enabled by the advent of the Phase II MWA’s compact configuration, which offers an enormous efficiency in beam-forming and processing costs, thereby making an all-sky survey of this magnitude tractable with the MWA. Even with the long dwell times employed for the survey (4800 s), data collection can be completed in $ $ 100 h of telescope time, while still retaining the ability to reach a limiting sensitivity of $\\sim$ 2–3 mJy (at 150 MHz, near zenith), which is effectively 3–5 times deeper than the previous-generation low-frequency southern-sky pulsar survey, completed in the 1990s. Each observation is processed to generate $\\sim$ 5000–8000 tied-array beams that tessellate the full $\\sim 610\\, {\\textrm{deg}^{2}}$ field of view (at 155 MHz), which are then processed to search for pulsars. The voltage-capture recording of the survey also allows a multitude of post hoc processing options including the reprocessing of data for higher time resolution and even exploring image-based techniques for pulsar candidate identification. Due to the substantial computational cost in pulsar searches at low frequencies, the survey data processing is undertaken in multiple passes: in the first pass, a shallow survey is performed, where 10 min of each observation is processed, reaching about one-third of the full-search sensitivity. Here we present the system overview including details of ongoing processing and initial results. Further details including first pulsar discoveries and a census of low-frequency detections are presented in a companion paper. Future plans include deeper searches to reach the full sensitivity and acceleration searches to target binary and millisecond pulsars. Our simulation analysis forecasts $\\sim$ 300 new pulsars upon the completion of full processing. The SMART survey will also generate a complete digital record of the low-frequency sky, which will serve as a valuable reference for future pulsar searches planned with the low-frequency Square Kilometre Array.
Publisher: Cambridge University Press (CUP)
Date: 2021
DOI: 10.1017/PASA.2021.15
Abstract: Here we present stringent low-frequency (185 MHz) limits on coherent radio emission associated with a short-duration gamma-ray burst (SGRB). Our observations of the short gamma-ray burst (GRB) 180805A were taken with the upgraded Murchison Widefield Array (MWA) rapid-response system, which triggered within 20s of receiving the transient alert from the Swift Burst Alert Telescope, corresponding to 83.7 s post-burst. The SGRB was observed for a total of 30 min, resulting in a $3\\sigma$ persistent flux density upper limit of 40.2 mJy beam –1 . Transient searches were conducted at the Swift position of this GRB on 0.5 s, 5 s, 30 s and 2 min timescales, resulting in $3\\sigma$ limits of 570–1 830, 270–630, 200–420, and 100–200 mJy beam –1 , respectively. We also performed a dedispersion search for prompt signals at the position of the SGRB with a temporal and spectral resolution of 0.5 s and 1.28 MHz, respectively, resulting in a $6\\sigma$ fluence upper-limit range from 570 Jy ms at DM $=3\\,000$ pc cm –3 ( $z\\sim 2.5$ ) to 1 750 Jy ms at DM $=200$ pc cm –3 ( $z\\sim 0.1)$ , corresponding to the known redshift range of SGRBs. We compare the fluence prompt emission limit and the persistent upper limit to SGRB coherent emission models assuming the merger resulted in a stable magnetar remnant. Our observations were not sensitive enough to detect prompt emission associated with the alignment of magnetic fields of a binary neutron star just prior to the merger, from the interaction between the relativistic jet and the interstellar medium (ISM) or persistent pulsar-like emission from the spin-down of the magnetar. However, in the case of a more powerful SGRB (a gamma-ray fluence an order of magnitude higher than GRB 180805A and/or a brighter X-ray counterpart), our MWA observations may be sensitive enough to detect coherent radio emission from the jet-ISM interaction and/or the magnetar remnant. Finally, we demonstrate that of all current low- frequency radio telescopes, only the MWA has the sensitivity and response times capable of probing prompt emission models associated with the initial SGRB merger event.
Publisher: SAGE Publications
Date: 04-05-2018
Abstract: Suicide rates in India are among the highest in the world, resulting in an estimated 250,000 suicide deaths annually. How the media communicates with the Indian public on the topic of suicide has thus far gone without sufficient scrutiny. The objective of our study was to assess the quality of newspaper reporting of suicide-related news in India against World Health Organization suicide reporting guidelines. We used content analysis to assess the quality of suicide reporting against World Health Organization guidelines in nine of the most highly read daily newspapers in the southern state of Tamil Nadu between June and December 2016. Five of the nine newspapers under review were in the top 20 most circulated daily newspapers in the country. A total of 1681 suicide articles were retrieved. The mean number of suicide articles per day per newspaper was 0.9%, and 54.5% of articles were 10 sentences or less. The vast majority (95.9%) of articles primarily focused on reporting specific suicide incidents. Harmful reporting practices were very common (e.g. a detailed suicide method was reported in 43.3% of articles), while helpful reporting practices were rare (e.g. just 2.5% gave contact details for a suicide support service). We observed that a daily diet of short and explicit suicide-related news was served up to readers of newspapers. Attempts should be made to understand the perspectives of media professionals in relation to suicide reporting, and to devise strategies to boost the positive contribution that media can make to suicide prevention.
Publisher: Elsevier BV
Date: 04-2022
DOI: 10.1016/J.JAD.2022.02.021
Abstract: Online searches related to suicide may sometimes be an early proxy indicator for behavioural outcomes. We used interrupted time series regression analyses to examine changes in suicide and resilience-related Google searches worldwide and in the United States during the first 12 months of the COVID-19 pandemic. Searches for the word "suicide" were unchanged worldwide (-1% 95%CI, -12%-11%) and in the US (-7% 95%CI, -15%-2%) with decreased searches for "suicide methods" and increased searches for "how to kill yourself" and for resilience-related terms. This study provides potential evidence that suicides may not increase worldwide during the first year of the pandemic.
Publisher: American Astronomical Society
Date: 29-10-2018
Publisher: Cambridge University Press (CUP)
Date: 2017
DOI: 10.1017/PASA.2017.54
Abstract: The Murchison Widefield Array (MWA), located in Western Australia, is one of the low-frequency precursors of the international Square Kilometre Array (SKA) project. In addition to pursuing its own ambitious science programme, it is also a testbed for wide range of future SKA activities ranging from hardware, software to data analysis. The key science programmes for the MWA and SKA require very high dynamic ranges, which challenges calibration and imaging systems. Correct calibration of the instrument and accurate measurements of source flux densities and polarisations require precise characterisation of the telescope’s primary beam. Recent results from the MWA GaLactic Extragalactic All-sky Murchison Widefield Array (GLEAM) survey show that the previously implemented Average Embedded Element (AEE) model still leaves residual polarisations errors of up to 10–20% in Stokes Q. We present a new simulation-based Full Embedded Element (FEE) model which is the most rigorous realisation yet of the MWA’s primary beam model. It enables efficient calculation of the MWA beam response in arbitrary directions without necessity of spatial interpolation. In the new model, every dipole in the MWA tile (4 × 4 bow-tie dipoles) is simulated separately, taking into account all mutual coupling, ground screen, and soil effects, and therefore accounts for the different properties of the in idual dipoles within a tile. We have applied the FEE beam model to GLEAM observations at 200–231 MHz and used false Stokes parameter leakage as a metric to compare the models. We have determined that the FEE model reduced the magnitude and declination-dependent behaviour of false polarisation in Stokes Q and V while retaining low levels of false polarisation in Stokes U.
Publisher: Elsevier BV
Date: 09-2022
Publisher: American Astronomical Society
Date: 23-08-2018
Publisher: Cambridge University Press (CUP)
Date: 2022
DOI: 10.1017/PASA.2022.14
Abstract: The Murchison Widefield Array (MWA) is a low-frequency aperture array capable of high-time and frequency resolution astronomy applications such as pulsar studies. The large field-of-view of the MWA (hundreds of square degrees) can also be exploited to attain fast survey speeds for all-sky pulsar search applications, but to maximise sensitivity requires forming thousands of tied-array beams from each voltage-capture observation. The necessity of using calibration solutions that are separated from the target observation both temporally and spatially makes pulsar observations vulnerable to uncorrected, frequency-dependent positional offsets due to the ionosphere. These offsets may be large enough to move the source away from the centre of the tied-array beam, incurring sensitivity drops of ${\\sim}30{-}50\\%$ in Phase II extended array configuration. We analyse these offsets in pulsar observations and develop a method for mitigating them, improving both the source position accuracy and the sensitivity. This analysis prompted the development of a multi-pixel beamforming functionality that can generate dozens of tied-array beams simultaneously, which runs a factor of ten times faster compared to the original single-pixel version. This enhancement makes it feasible to observe multiple pulsars within the vast field of view of the MWA and supports the ongoing large-scale pulsar survey efforts with the MWA. We explore the extent to which ionospheric offset correction will be necessary for the MWA Phase III and the low-frequency square kilometre array (SKA-low).
Publisher: Oxford University Press (OUP)
Date: 22-11-2022
Abstract: We present a targeted search for low-frequency (144–215 MHz) fast radio burst (FRB) emission from five repeating FRBs using 23.3 h of archival data taken with the Murchison Widefield Array (MWA) voltage capture system (VCS) between 2014 September and 2020 May. This is the first time that the MWA VCS has been used to search for FRB signals from known repeaters, which enables much more sensitive FRB searches than previously performed with the standard MWA correlator mode. We performed a standard single-pulse search with a temporal and spectral resolution of $400\\, \\mu$s and 10 kHz, respectively, over a $100\\, \\text{pc}\\, \\text{cm}^{-3}$ dispersion measure (DM) range centred at the known DM of each studied repeating FRB. No FRBs exceeding a 6σ threshold were detected. The fluence upper limits in the range of 32–1175 and 36–488 Jy ms derived from 10 observations of FRB 20190711A and four observations of FRB 20201124A, respectively, allow us to constrain the spectral indices of their bursts to ≳−1 if these two repeaters were active during the MWA observations. If free–free absorption is responsible for our non-detection, we can constrain the size of the absorbing medium in terms of the electron temperature T to ${\\lt} 1.00\\times (T/10^4\\,\\text{K})^{-1.35}\\, \\text{pc}$, ${\\lt} 0.92\\times (T/10^4\\,\\text{K})^{-1.35}\\, \\text{pc}$, and ${\\lt} [0.22\\!-\\!2.50]\\times (T/10^4\\,\\text{K})^{-1.35}\\, \\text{pc}$ for FRB 20190117A, FRB 20190711A, and FRB 20201124A, respectively. However, given that the activities of these repeaters are not well characterized, our non-detections could also suggest they were inactive during the MWA observations.
No related grants have been discovered for Thomas Niederkrotenthaler.