ORCID Profile
0000-0002-5119-4808
Current Organisation
Curtin University
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Research Topics
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Top 5 Research Topics
ANZSRC Field of Research (FoR)
Astronomical and Space Sciences | Cosmology and Extragalactic Astronomy | Galactic Astronomy | Astronomical and Space Instrumentation | Space and Solar Physics |
ANZSRC Socio-Economic Objective (SEO)
Expanding Knowledge in the Physical Sciences | Scientific Instruments | Information Processing Services (incl. Data Entry and Capture) | Expanding Knowledge in Technology | Environmentally Sustainable Construction not elsewhere classified
Related Links
Publications
AMI observations of northern supernova remnants at 14-18 GHz
Publisher: Oxford University Press (OUP)
Date: 11-06-2009
Follow-up observations at 16 and 33���GHz of extragalactic sources fromWMAP3-yr data: II ��� Flux density variability
Publisher: Oxford University Press (OUP)
Date: 12-2009
Calibration database for the Murchison Widefield Array All-Sky Virtual Observatory
Publisher: Cambridge University Press (CUP)
Date: 2020
DOI: 10.1017/PASA.2020.17
Abstract: We present a calibration component for the Murchison Widefield Array All-Sky Virtual Observatory (MWA ASVO) utilising a newly developed PostgreSQL database of calibration solutions. Since its inauguration in 2013, the MWA has recorded over 34 petabytes of data archived at the Pawsey Supercomputing Centre. According to the MWA Data Access policy, data become publicly available 18 months after collection. Therefore, most of the archival data are now available to the public. Access to public data was provided in 2017 via the MWA ASVO interface, which allowed researchers worldwide to download MWA uncalibrated data in standard radio astronomy data formats (CASA measurement sets or UV FITS files). The addition of the MWA ASVO calibration feature opens a new, powerful avenue for researchers without a detailed knowledge of the MWA telescope and data processing to download calibrated visibility data and create images using standard radio astronomy software packages. In order to populate the database with calibration solutions from the last 6 yr we developed fully automated pipelines. A near-real-time pipeline has been used to process new calibration observations as soon as they are collected and upload calibration solutions to the database, which enables monitoring of the interferometric performance of the telescope. Based on this database, we present an analysis of the stability of the MWA calibration solutions over long time intervals.
The discovery of an unusual repeating radio transient
Publisher: Universite de Geneve
Date: 22-08-2022
Abstract: We have discovered a new kind of repeating radio source using a sensitive low-frequency radio telescope in outback Western Australia. Its unusual properties indicate it could be a kind of never-before-detected object: an ultra-long-period magnetar.
Modelling and peeling extended sources with shapelets: A Fornax A case study
Publisher: Cambridge University Press (CUP)
Date: 2020
DOI: 10.1017/PASA.2020.18
Abstract: To make a power spectrum (PS) detection of the 21-cm signal from the Epoch of Reionisation (EoR), one must avoid/subtract bright foreground sources. Sources such as Fornax A present a modelling challenge due to spatial structures spanning from arc seconds up to a degree. We compare modelling with multi-scale (MS) CLEAN components to ‘shapelets’, an alternative set of basis functions. We introduce a new image-based shapelet modelling package, SHAMFI. We also introduce a new CUDA simulation code (WODEN) to generate point source, Gaussian, and shapelet components into visibilities. We test performance by modelling a simulation of Fornax A, peeling the model from simulated visibilities, and producing a residual PS. We find the shapelet method consistently subtracts large-angular-scale emission well, even when the angular resolution of the data is changed. We find that when increasing the angular resolution of the data, the MS CLEAN model worsens at large angular scales. When testing on real Murchison Widefield Array data, the expected improvement is not seen in real data because of the other dominating systematics still present. Through further simulation, we find the expected differences to be lower than obtainable through current processing pipelines. We conclude shapelets are worthwhile for subtracting extended galaxies, and may prove essential for an EoR detection in the future, once other systematics have been addressed.
The spectral energy distribution of powerful starburst galaxies – I. Modelling the radio continuum
Publisher: Oxford University Press (OUP)
Date: 09-10-2017
Searching for the Synchrotron Cosmic Web Again: A replication attempt - ADDENDUM
Publisher: Cambridge University Press (CUP)
Date: 2022
DOI: 10.1017/PASA.2022.39
Radio observations of supernova remnant G1.9+0.3
Publisher: Oxford University Press (OUP)
Date: 09-12-2019
Abstract: We present 1–10 GHz radio continuum flux density, spectral index, polarization, and rotation measure (RM) images of the youngest known Galactic supernova remnant (SNR) G1.9+0.3, using observations from the Australia Telescope Compact Array. We have conducted an expansion study spanning eight epochs between 1984 and 2017, yielding results consistent with previous expansion studies of G1.9+0.3. We find a mean radio continuum expansion rate of (0.78 ± 0.09) per cent yr−1 (or ∼8900 km s−1 at an assumed distance of 8.5 kpc), although the expansion rate varies across the SNR perimetre. In the case of the most recent epoch between 2016 and 2017, we observe faster-than-expected expansion of the northern region. We find a global spectral index for G1.9+0.3 of −0.81 ± 0.02 (76 MHz–10 GHz). Towards the northern region, however, the radio spectrum is observed to steepen significantly (∼−1). Towards the two so-called (east and west) ‘ears’ of G1.9+0.3, we find very different RM values of 400–600 and 100–200 rad m2, respectively. The fractional polarization of the radio continuum emission reaches (19 ± 2) per cent, consistent with other, slightly older, SNRs such as Cas A.
Radio continuum observations of Class I protostellar discs in Taurus: constraining the greybody tail at centimetre wavelengths★
Publisher: Oxford University Press (OUP)
Date: 09-02-2012
Towards net zero emissions, recovered silicon from recycling PV waste panels for silicon carbide crystal production
Publisher: Elsevier BV
Date: 07-2023
GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey III: South Galactic Pole data release
Publisher: Cambridge University Press (CUP)
Date: 2021
DOI: 10.1017/PASA.2021.5
Abstract: We present the South Galactic Pole (SGP) data release from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. These data combine both years of GLEAM observations at 72–231 MHz conducted with the Murchison Widefield Array (MWA) and cover an area of 5 113 $\\mathrm{deg}^{2}$ centred on the SGP at $20^{\\mathrm{h}} 40^{\\mathrm{m}} \\mathrm{RA} 05^{\\mathrm{h}} 04^{\\mathrm{m}}$ and $-48^{\\circ} \\mathrm{Dec} -2^{\\circ} $ . At 216 MHz, the typical rms noise is ${\\approx}5$ mJy beam –1 and the angular resolution ${\\approx}2$ arcmin. The source catalogue contains a total of 108 851 components above $5\\sigma$ , of which 77% have measured spectral indices between 72 and 231 MHz. Improvements to the data reduction in this release include the use of the GLEAM Extragalactic catalogue as a sky model to calibrate the data, a more efficient and automated algorithm to deconvolve the snapshot images, and a more accurate primary beam model to correct the flux scale. This data release enables more sensitive large-scale studies of extragalactic source populations as well as spectral variability studies on a one-year timescale.
Estimating the Jet Power of Mrk 231 during the 2017–2018 Flare
Publisher: American Astronomical Society
Date: 04-03-2020
Further Sunyaev-Zel’dovich observations of two Planck ERCSC clusters with the Arcminute Microkelvin Imager★
Publisher: Oxford University Press (OUP)
Date: 09-05-2011
10C survey of radio sources at 15.7 GHz - I. Observing, mapping and source extraction★
Publisher: Oxford University Press (OUP)
Date: 28-06-2011
The POlarised GLEAM Survey (POGS) II: Results from an all-sky rotation measure synthesis survey at long wavelengths
Publisher: Cambridge University Press (CUP)
Date: 2020
DOI: 10.1017/PASA.2020.20
Abstract: The low-frequency linearly polarised radio source population is largely unexplored. However, a renaissance in low-frequency polarimetry has been enabled by pathfinder and precursor instruments for the Square Kilometre Array. In this second paper from the POlarised GaLactic and Extragalactic All-Sky MWA Survey-the POlarised GLEAM Survey, or POGS-we present the results from our all-sky MWA Phase I Faraday Rotation Measure survey. Our survey covers nearly the entire Southern sky in the Declination range $-82^\\circ$ to $+30^\\circ$ at a resolution between around three and seven arcminutes (depending on Declination) using data in the frequency range 169−231 MHz. We have performed two targeted searches: the first covering 25 489 square degrees of sky, searching for extragalactic polarised sources the second covering the entire sky South of Declination $+30^\\circ$ , searching for known pulsars. We detect a total of 517 sources with 200 MHz linearly polarised flux densities between 9.9 mJy and 1.7 Jy, of which 33 are known radio pulsars. All sources in our catalogues have Faraday rotation measures in the range $-328.07$ to $+279.62$ rad m −2 . The Faraday rotation measures are broadly consistent with results from higher-frequency surveys, but with typically more than an order of magnitude improvement in the precision, highlighting the power of low-frequency polarisation surveys to accurately study Galactic and extragalactic magnetic fields. We discuss the properties of our extragalactic and known-pulsar source population, how the sky distribution relates to Galactic features, and identify a handful of new pulsar candidates among our nominally extragalactic source population.
The Arcminute Microkelvin Imager★
Publisher: Oxford University Press (OUP)
Date: 21-12-2008
Follow-up observations at 16 and 33���GHz of extragalactic sources fromWMAP3-yr data: I ��� Spectral properties
Publisher: Oxford University Press (OUP)
Date: 12-2009
Arcminute microkelvin imager observations of unmatched Planck ERCSC LFI sources at 15.75GHz
Publisher: Oxford University Press (OUP)
Date: 03-2012
DOI: 10.1111/J.1745-3933.2011.01195.X
Abstract: The Planck Early Release Compact Source Catalogue includes 26 sources with no obvious matches in other radio catalogues (of predominantly extragalactic sources). Here we present observations made with the Arcminute Microkelvin Imager Small Array (AMI SA) at 15.75 GHz of the eight unmatched sources at δ +10°. Of the eight, four are detected and are associated with known objects. The other four are not detected with the AMI SA, and are thought to be spurious.
The GLEAMing of the first supermassive black holes: II. A new sample of high-redshift radio galaxy candidates
Publisher: Cambridge University Press (CUP)
Date: 2022
DOI: 10.1017/PASA.2022.42
Abstract: While unobscured and radio-quiet active galactic nuclei are regularly being found at redshifts $z 6$ , their obscured and radio-loud counterparts remain elusive. We build upon our successful pilot study, presenting a new s le of low-frequency-selected candidate high-redshift radio galaxies (HzRGs) over a sky area 20 times larger. We have refined our selection technique, in which we select sources with curved radio spectra between 72–231 MHz from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. In combination with the requirements that our GLEAM-selected HzRG candidates have compact radio morphologies and be undetected in near-infrared $K_{\\rm s}$ -band imaging from the Visible and Infrared Survey Telescope for Astronomy Kilo-degree Infrared Galaxy (VIKING) survey, we find 51 new candidate HzRGs over a sky area of approximately $1200\\ \\mathrm{deg}^2$ . Our s le also includes two sources from the pilot study: the second-most distant radio galaxy currently known, at $z=5.55$ , with another source potentially at $z \\sim 8$ . We present our refined selection technique and analyse the properties of the s le. We model the broadband radio spectra between 74 MHz and 9 GHz by supplementing the GLEAM data with both publicly available data and new observations from the Australia Telescope Compact Array at 5.5 and 9 GHz. In addition, deep $K_{\\rm s}$ -band imaging from the High-Acuity Widefield K -band Imager (HAWK-I) on the Very Large Telescope and from the Southern Herschel Astrophysical Terahertz Large Area Survey Regions $K_{\\rm s}$ -band Survey (SHARKS) is presented for five sources. We discuss the prospects of finding very distant radio galaxies in our s le, potentially within the epoch of reionisation at $z \\gtrsim 6.5$ .
The most probable host of CHIME FRB 190425A, associated with binary neutron star merger GW190425, and a late-time transient search
Publisher: Oxford University Press (OUP)
Date: 09-12-2022
Abstract: The identification and localization of fast radio bursts (FRBs) to their host galaxies have revealed important details about the progenitors of these mysterious, millisecond-long bursts of coherent radio emission. In this work, we study the most probable host galaxy of the apparently non-repeating CHIME/FRB event FRB 20190425A – a particularly high-luminosity, low-dispersion measure event that was demonstrated in a recent paper to be temporally and spatially coincident with the LIGO-Virgo-KAGRA binary neutron star merger GW190425, suggesting an astrophysical association (p-value 0.0052). In this paper, we remain agnostic to this result, and we confirm UGC10667 as the most probable host galaxy of FRB 20190425A, demonstrating that the host galaxies of low-dispersion measure, one-off CHIME FRBs can be plausibly identified. We then perform multiwavelength observations to characterize the galaxy and search for any afterglow emission associated with the FRB and its putative GW counterpart. We find no radio or optical transient emission in our observations $2.5\\, \\mathrm{yr}$ post-burst. UGC10667 is a spiral galaxy at z ∼ 0.03, dominated by an old stellar population. We find no evidence of a large population of young stars, with nebular emission dominated by star formation at a rate of $1\\!-\\!2\\, ~\\mathrm{M_\\odot \\, yr^{-1}}$. While we cannot rule out a young magnetar as the origin of FRB 20190425A, our observations are consistent with an origin in a long delay-time neutron star binary merger.
Nitric Oxide and Other Molecules: Molecular Modeling and Low-frequency Exploration Using the Murchison Widefield Array
Publisher: American Astronomical Society
Date: 12-2020
GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey II: Galactic plane 345° <l< 67°, 180° <l< 240°
Publisher: Cambridge University Press (CUP)
Date: 2019
DOI: 10.1017/PASA.2019.37
Abstract: This work makes available a further $2\,860~\text{deg}^2$ of the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey, covering half of the accessible galactic plane, across 20 frequency bands s ling 72–231 MHz, with resolution $4\,\text{arcmin}-2\,\text{arcmin}$ . Unlike previous GLEAM data releases, we used multi-scale CLEAN to better deconvolve large-scale galactic structure. For the galactic longitude ranges $345^\circ l 67^\circ$ , $180^\circ l 240^\circ$ , we provide a compact source catalogue of 22 037 components selected from a 60-MHz bandwidth image centred at 200 MHz, with RMS noise $\approx10-20\,\text{mJy}\,\text{beam}^{-1}$ and position accuracy better than 2 arcsec. The catalogue has a completeness of 50% at ${\approx}120\,\text{mJy}$ , and a reliability of 99.86%. It covers galactic latitudes $1^\circ\leq|b|\leq10^\circ$ towards the galactic centre and $|b|\leq10^\circ$ for other regions, and is available from Vizier images covering $|b|\leq10^\circ$ for all longitudes are made available on the GLEAM Virtual Observatory (VO).server and SkyView.
High-energy sources at low radio frequency: the Murchison Widefield Array view ofFermiblazars
Publisher: EDP Sciences
Date: 04-2016
Early-Time searches for coherent radio emission from short GRBs with the Murchison Widefield Array
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.
Candidate radio supernova remnants observed by the GLEAM survey over 345° <l< 60° and 180° <l< 240°
Publisher: Cambridge University Press (CUP)
Date: 2019
DOI: 10.1017/PASA.2019.33
Abstract: We examined the latest data release from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey covering 345° l 60° and 180° l 240°, using these data and that of the Widefield Infrared Survey Explorer to follow up proposed candidate Supernova Remnant (SNR) from other sources. Of the 101 candidates proposed in the region, we are able to definitively confirm ten as SNRs, tentatively confirm two as SNRs, and reclassify five as H ii regions. A further two are detectable in our images but difficult to classify the remaining 82 are undetectable in these data. We also investigated the 18 unclassified Multi-Array Galactic Plane Imaging Survey (MAGPIS) candidate SNRs, newly confirming three as SNRs, reclassifying two as H ii regions, and exploring the unusual spectra and morphology of two others.
New candidate radio supernova remnants detected in the GLEAM survey over 345° <l< 60°, 180° <l< 240°
Publisher: Cambridge University Press (CUP)
Date: 2019
DOI: 10.1017/PASA.2019.34
Abstract: We have detected 27 new supernova remnants (SNRs) using a new data release of the GLEAM survey from the Murchison Widefield Array telescope, including the lowest surface brightness SNR ever detected, G 0.1 – 9.7. Our method uses spectral fitting to the radio continuum to derive spectral indices for 26/27 candidates, and our low-frequency observations probe a steeper spectrum population than previously discovered. None of the candidates have coincident WISE mid-IR emission, further showing that the emission is non-thermal. Using pulsar associations we derive physical properties for six candidate SNRs, finding G 0.1 – 9.7 may be younger than 10 kyr. Sixty per cent of the candidates subtend areas larger than 0.2 deg 2 on the sky, compared to 25% of previously detected SNRs. We also make the first detection of two SNRs in the Galactic longitude range 220°–240°.
AMI-LA radio continuum observations of Spitzer c2d small clouds and cores: Perseus region
Publisher: Oxford University Press (OUP)
Date: 06-2011
A blazar-like radio flare in MRK 231
Publisher: American Astronomical Society
Date: 03-10-2013
Sunyaev-Zel'dovich observations with AMI of the hottest galaxy clusters detected in the XMM-newton cluster survey
Publisher: Oxford University Press (OUP)
Date: 29-06-2013
DOI: 10.1093/MNRAS/STT932
Source Finding in the Era of the SKA (Precursors): Aegean 2.0
Publisher: Cambridge University Press (CUP)
Date: 2018
DOI: 10.1017/PASA.2018.3
Abstract: In the era of the SKA precursors, telescopes are producing deeper, larger images of the sky on increasingly small time-scales. The greater size and volume of images place an increased demand on the software that we use to create catalogues, and so our source finding algorithms need to evolve accordingly. In this paper, we discuss some of the logistical and technical challenges that result from the increased size and volume of images that are to be analysed, and demonstrate how the Aegean source finding package has evolved to address these challenges. In particular, we address the issues of source finding on spatially correlated data, and on images in which the background, noise, and point spread function vary across the sky. We also introduce the concept of forced or prioritised fitting.
Searching for dark matter signals from local dwarf spheroidal galaxies at low radio frequencies in the GLEAM survey
Publisher: Oxford University Press (OUP)
Date: 17-03-2020
Abstract: The search for emission from weakly interacting massive particle (WIMP) dark matter annihilation and decay has become a multipronged area of research not only targeting a erse selection of astrophysical objects, but also taking advantage of the entire electromagnetic spectrum. The decay of WIMP particles into standard model particles has been suggested as a possible channel for synchrotron emission to be detected at low radio frequencies. Here, we present the stacking analysis of a s le of 33 dwarf spheroidal (dSph) galaxies with low-frequency (72–231 MHz) radio images from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. We produce radial surface brightness profiles of images centred upon each dSph galaxy with background radio sources masked. We remove 10 fields from the stacking due to contamination from either poorly subtracted, bright radio sources or strong background gradients across the field. The remaining 23 dSph galaxies are stacked in an attempt to obtain a statistical detection of any WIMP-induced synchrotron emission in these systems. We find that the stacked radial brightness profile does not exhibit a statistically significant detection above the 95 per cent confidence level of ∼1.5 mJy beam−1. This novel technique shows the potential of using low-frequency radio images to constrain fundamental properties of particle dark matter.
Galactic synchrotron distribution derived from 152 H ii region absorption features in the full GLEAM survey
Publisher: Oxford University Press (OUP)
Date: 29-06-2018
G17.8 + 16.7: A new supernova remnant
Publisher: Oxford University Press (OUP)
Date: 07-12-2021
Abstract: Non-thermal radio emission is detected in the region of the gamma-ray source FHES J1723.5 − 0501. The emission has an approximately circular shape 0.8° in diameter. The observations confirm its nature as a new supernova remnant, G 17.8 + 16.7. We derive constraints on the source parameters using the radio data and gamma-ray observations of the region. The distance to the object is possibly in the range 1.4–3.5 kpc. An SNR age of the order of 10 kyr is compatible with the radio and GeV features, but an older or younger SNR cannot be ruled out. A simple one-zone leptonic model naturally explains the multi-wavelength non-thermal fluxes of the source at its location outside the Galactic plane.
CHIPS: THE COSMOLOGICAL H i POWER SPECTRUM ESTIMATOR
Publisher: American Astronomical Society
Date: 18-02-2016
The GLEAM 4-Jy (G4Jy) Sample: II. Host galaxy identification for individual sources
Publisher: Cambridge University Press (CUP)
Date: 2020
DOI: 10.1017/PASA.2020.10
Abstract: The entire southern sky (Declination, $\delta 30^{\circ}$ ) has been observed using the Murchison Widefield Array (MWA), which provides radio imaging of $\sim$ 2 arcmin resolution at low frequencies (72–231 MHz). This is the GaLactic and Extragalactic All-sky MWA (GLEAM) Survey, and we have previously used a combination of visual inspection, cross-checks against the literature, and internal matching to identify the ‘brightest’ radio-sources ( $S_{\mathrm{151\,MHz}} $ Jy) in the extragalactic catalogue (Galactic latitude, $|b| ^{\circ}$ ). We refer to these 1 863 sources as the GLEAM 4-Jy (G4Jy) S le, and use radio images (of ${\leq}45$ arcsec resolution), and multi-wavelength information, to assess their morphology and identify the galaxy that is hosting the radio emission (where appropriate). Details of how to access all of the overlays used for this work are available at vw26/G4Jy . Alongside this we conduct further checks against the literature, which we document here for in idual sources. Whilst the vast majority of the G4Jy S le are active galactic nuclei with powerful radio-jets, we highlight that it also contains a nebula, two nearby, star-forming galaxies, a cluster relic, and a cluster halo. There are also three extended sources for which we are unable to infer the mechanism that gives rise to the low-frequency emission. In the G4Jy catalogue we provide mid-infrared identifications for 86% of the sources, and flag the remainder as: having an uncertain identification (129 sources), having a faint/uncharacterised mid-infrared host (126 sources), or it being inappropriate to specify a host (2 sources). For the subset of 129 sources, there is ambiguity concerning candidate host-galaxies, and this includes four sources (B0424–728, B0703–451, 3C 198, and 3C 403.1) where we question the existing identification.
THE MURCHISON WIDEFIELD ARRAY 21 cm POWER SPECTRUM ANALYSIS METHODOLOGY
Publisher: American Astronomical Society
Date: 11-07-2016
EMU Detection of a Large and Low Surface Brightness Galactic SNR G288.8–6.3
Publisher: American Astronomical Society
Date: 07-09-2023
The radio source count at 93.2 GHz from observations of 9C sources using AMI and CARMA
Publisher: Oxford University Press (OUP)
Date: 02-2013
DOI: 10.1093/MNRAS/STT016
An excess of emission in the dark cloud LDN 1111 with the Arcminute Microkelvin Imager
Publisher: Oxford University Press (OUP)
Date: 21-03-2009
A search for long-time-scale, low-frequency radio transients
Publisher: Oxford University Press (OUP)
Date: 30-11-2016
A High-Resolution Foreground Model for the MWA EoR1 Field: Model and Implications for EoR Power Spectrum Analysis
Publisher: Cambridge University Press (CUP)
Date: 2017
DOI: 10.1017/PASA.2017.26
Abstract: The current generation of experiments aiming to detect the neutral hydrogen signal from the Epoch of Reionisation (EoR) is likely to be limited by systematic effects associated with removing foreground sources from target fields. In this paper, we develop a model for the compact foreground sources in one of the target fields of the MWA’s EoR key science experiment: the ‘EoR1’ field. The model is based on both the MWA’s GLEAM survey and GMRT 150 MHz data from the TGSS survey, the latter providing higher angular resolution and better astrometric accuracy for compact sources than is available from the MWA alone. The model contains 5 049 sources, some of which have complicated morphology in MWA data, Fornax A being the most complex. The higher resolution data show that 13% of sources that appear point-like to the MWA have complicated morphology such as double and quad structure, with a typical separation of 33 arcsec. We derive an analytic expression for the error introduced into the EoR two-dimensional power spectrum due to peeling close double sources as single point sources and show that for the measured source properties, the error in the power spectrum is confined to high k ⊥ modes that do not affect the overall result for the large-scale cosmological signal of interest. The brightest 10 mis-modelled sources in the field contribute 90% of the power bias in the data, suggesting that it is most critical to improve the models of the brightest sources. With this hybrid model, we reprocess data from the EoR1 field and show a maximum of 8% improved calibration accuracy and a factor of two reduction in residual power in k -space from peeling these sources. Implications for future EoR experiments including the SKA are discussed in relation to the improvements obtained.
Limits on Fast Radio Bursts and other transient sources at 182 MHz using the Murchison Widefield Array
Publisher: Oxford University Press (OUP)
Date: 03-2016
DOI: 10.1093/MNRAS/STW451
High time resolution search for prompt radio emission from the long GRB 210419A with the Murchison Widefield Array
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.
First limits on the 21 cm power spectrum during the Epoch of X-ray heating
Publisher: Oxford University Press (OUP)
Date: 19-05-2016
Bright radio emission from an ultraluminous stellar-mass microquasar in M 31
Publisher: Springer Science and Business Media LLC
Date: 12-12-2012
DOI: 10.1038/NATURE11697
Abstract: A subset of ultraluminous X-ray sources (those with luminosities of less than 10(40) erg s(-1) ref. 1) are thought to be powered by the accretion of gas onto black holes with masses of ∼5-20M cicled dot, probably by means of an accretion disk. The X-ray and radio emission are coupled in such Galactic sources the radio emission originates in a relativistic jet thought to be launched from the innermost regions near the black hole, with the most powerful emission occurring when the rate of infalling matter approaches a theoretical maximum (the Eddington limit). Only four such maximal sources are known in the Milky Way, and the absorption of soft X-rays in the interstellar medium hinders the determination of the causal sequence of events that leads to the ejection of the jet. Here we report radio and X-ray observations of a bright new X-ray source in the nearby galaxy M 31, whose peak luminosity exceeded 10(39) erg s(-1). The radio luminosity is extremely high and shows variability on a timescale of tens of minutes, arguing that the source is highly compact and powered by accretion close to the Eddington limit onto a black hole of stellar mass. Continued radio and X-ray monitoring of such sources should reveal the causal relationship between the accretion flow and the powerful jet emission.
High-resolution AMI Large Array imaging of spinning dust sources: spatially correlated 8 μm emission and evidence of a stellar wind in L675
Publisher: Oxford University Press (OUP)
Date: 21-03-2010
Detailed Sunyaev-Zel'dovich study with AMI of 19 LoCuSS galaxy clusters: Masses and temperatures out to the virial radius
Publisher: Oxford University Press (OUP)
Date: 02-08-2012
FIRST SEASON MWA EOR POWER SPECTRUM RESULTS AT REDSHIFT 7
Publisher: American Astronomical Society
Date: 09-12-2016
De-distorting ionospheric effects in the image plane
Publisher: Elsevier BV
Date: 10-2018
The Location of Young Pulsar PSR J0837–2454: Galactic Halo or Local Supernova Remnant?
Publisher: American Astronomical Society
Date: 04-2021
Abstract: We present the discovery and timing of the young (age ∼28.6 kyr) pulsar PSR J0837–2454. Based on its high latitude ( b = 98) and dispersion measure (DM = 143 pc cm −3 ), the pulsar appears to be at a z -height of kpc above the Galactic plane, but near the edge of our Galaxy. This is many times the observed scale height of the canonical pulsar population, which suggests this pulsar may have been born far out of the plane. If accurate, the young age and high z -height imply that this is the first pulsar known to be born from a runaway O/B star. In follow-up imaging with the Australia Telescope Compact Array (ATCA), we detect the pulsar with a flux density S 1400 = 0.18 ± 0.05 mJy. We do not detect an obvious supernova remnant around the pulsar in our ATCA data, but we detect a colocated, low-surface-brightness region of ∼15 extent in archival Galactic and Extragalactic All-sky MWA Survey data. We also detect colocated H α emission from the Southern H α Sky Survey Atlas. Distance estimates based on these two detections come out to ∼0.9 kpc and ∼0.2 kpc, respectively, both of which are much smaller than the distance predicted by the NE2001 model (6.3 kpc) and YMW model ( kpc) and place the pulsar much closer to the plane of the Galaxy. If the pulsar/remnant association holds, this result also highlights the inherent difficulty in the classification of transients as “Galactic” (pulsar) or “extragalactic” (fast radio burst) toward the Galactic anticenter based solely on the modeled Galactic electron contribution to a detection.
ON THE DETECTION AND TRACKING OF SPACE DEBRIS USING THE MURCHISON WIDEFIELD ARRAY. I. SIMULATIONS AND TEST OBSERVATIONS DEMONSTRATE FEASIBILITY
Publisher: American Astronomical Society
Date: 16-09-2013
Science with the Murchison Widefield Array: Phase I results and Phase II opportunities
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.
10C survey of radio sources at 15.7 GHz - II. First results★
Publisher: Oxford University Press (OUP)
Date: 28-06-2011
The GLEAM 4-Jy (G4Jy) Sample: I. Definition and the catalogue
Publisher: Cambridge University Press (CUP)
Date: 2020
DOI: 10.1017/PASA.2020.9
Abstract: The Murchison Widefield Array (MWA) has observed the entire southern sky (Declination, $\delta 30^{\circ}$ ) at low radio frequencies, over the range 72–231MHz. These observations constitute the GaLactic and Extragalactic All-sky MWA (GLEAM) Survey, and we use the extragalactic catalogue (EGC) (Galactic latitude, $|b| ^{\circ}$ ) to define the GLEAM 4-Jy (G4Jy) S le. This is a complete s le of the ‘brightest’ radio sources ( $S_{\textrm{151\,MHz}} \,\text{Jy}$ ), the majority of which are active galactic nuclei with powerful radio jets. Crucially, low-frequency observations allow the selection of such sources in an orientation-independent way (i.e. minimising the bias caused by Doppler boosting, inherent in high-frequency surveys). We then use higher-resolution radio images, and information at other wavelengths, to morphologically classify the brightest components in GLEAM. We also conduct cross-checks against the literature and perform internal matching, in order to improve s le completeness (which is estimated to be $ .5$ %). This results in a catalogue of 1863 sources, making the G4Jy S le over 10 times larger than that of the revised Third Cambridge Catalogue of Radio Sources (3CRR $S_{\textrm{178\,MHz}} .9\,\text{Jy}$ ). Of these G4Jy sources, 78 are resolved by the MWA (Phase-I) synthesised beam ( $\sim2$ arcmin at 200MHz), and we label 67% of the s le as ‘single’, 26% as ‘double’, 4% as ‘triple’, and 3% as having ‘complex’ morphology at $\sim1\,\text{GHz}$ (45 arcsec resolution). We characterise the spectral behaviour of these objects in the radio and find that the median spectral index is $\alpha=-0.740 \pm 0.012$ between 151 and 843MHz, and $\alpha=-0.786 \pm 0.006$ between 151MHz and 1400MHz (assuming a power-law description, $S_{\nu} \propto \nu^{\alpha}$ ), compared to $\alpha=-0.829 \pm 0.006$ within the GLEAM band. Alongside this, our value-added catalogue provides mid-infrared source associations (subject to 6” resolution at 3.4 $\mu$ m) for the radio emission, as identified through visual inspection and thorough checks against the literature. As such, the G4Jy S le can be used as a reliable training set for cross-identification via machine-learning algorithms. We also estimate the angular size of the sources, based on their associated components at $\sim1\,\text{GHz}$ , and perform a flux density comparison for 67 G4Jy sources that overlap with 3CRR. Analysis of multi-wavelength data, and spectral curvature between 72MHz and 20GHz, will be presented in subsequent papers, and details for accessing all G4Jy overlays are provided at vw26/G4Jy .
AMI Large Array radio continuum observations of Spitzer c2d small clouds and cores★
Publisher: Oxford University Press (OUP)
Date: 12-11-2010
AMI-LA radio continuum observations of Spitzer c2d small clouds and cores: Serpens region
Publisher: Oxford University Press (OUP)
Date: 30-12-2012
Low Altitude Solar Magnetic Reconnection, Type III Solar Radio Bursts, and X-ray Emissions
Publisher: Springer Science and Business Media LLC
Date: 26-01-2018
DOI: 10.1038/S41598-018-19195-3
Abstract: Type III solar radio bursts are the Sun’s most intense and frequent nonthermal radio emissions. They involve two critical problems in astrophysics, plasma physics, and space physics: how collective processes produce nonthermal radiation and how magnetic reconnection occurs and changes magnetic energy into kinetic energy. Here magnetic reconnection events are identified definitively in Solar Dynamics Observatory UV-EUV data, with strong upward and downward pairs of jets, current sheets, and cusp-like geometries on top of time-varying magnetic loops, and strong outflows along pairs of open magnetic field lines. Type III bursts imaged by the Murchison Widefield Array and detected by the Learmonth radiospectrograph and STEREO B spacecraft are demonstrated to be in very good temporal and spatial coincidence with specific reconnection events and with bursts of X-rays detected by the RHESSI spacecraft. The reconnection sites are low, near heights of 5–10 Mm. These images and event timings provide the long-desired direct evidence that semi-relativistic electrons energized in magnetic reconnection regions produce type III radio bursts. Not all the observed reconnection events produce X-ray events or coronal or interplanetary type III bursts thus different special conditions exist for electrons leaving reconnection regions to produce observable radio, EUV, UV, and X-ray bursts.
Erratum: Science with the murchison widefield array: Phase I results and phase II opportunities (Publications of the Astronomical Society of Australia (2019) 36 (1-30) DOI: 10.1017/pasa.2019.41)
Publisher: Cambridge University Press (CUP)
Date: 2020
DOI: 10.1017/PASA.2020.4
Hoinga: a supernova remnant discovered in the SRG/eROSITA All-Sky Survey eRASS1
Publisher: EDP Sciences
Date: 04-2021
DOI: 10.1051/0004-6361/202040156
Abstract: Supernova remnants (SNRs) are observable for about (6−15) × 10 4 yr before they fade into the Galactic interstellar medium. With a Galactic supernova rate of approximately two per century, we can expect to have of the order of 1200 SNRs in our Galaxy. However, only about 300 of them are known to date, with the majority having been discovered in Galactic plane radio surveys. Given that these SNRs represent the brightest tail of the distribution and are mostly located close to the plane, they are not representative of the complete s le. The launch of the Russian-German observatory SRG/eROSITA in July 2019 brought a promising new opportunity to explore the Universe. Here we report findings from the search for new SNRs in the eROSITA all-sky survey data which led to the detection of one of the largest SNRs discovered at wavelengths other than the radio: G249.5+24.5. This source is located at a relatively high Galactic latitude, where SNRs are not usually expected to be found. The remnant, ‘Hoinga’, has a diameter of about 4. °4 and shows a circular shaped morphology with diffuse X-ray emission filling almost the entire remnant. Spectral analysis of the remnant emission reveals that an APEC spectrum from collisionally ionised diffuse gas and a plane-parallel shock plasma model with non-equilibrium ionisation are both able to provide an adequate description of the data, suggesting a gas temperature of the order of kT = 0.1 −0.02 +0.02 keV and an absorbing column density of N H = 3.6 −0.6 +0.7 × 10 20 cm −2 . Various X-ray point sources are found to be located within the remnant boundary but none seem to be associated with the remnant itself. Subsequent searches for a radio counterpart of the Hoinga remnant identified its radio emission in archival data from the Continuum HI Parkes All-Sky Survey and the 408-MHz ‘Haslam’ all-sky survey. The radio spectral index α = −0.69 ± 0.08 obtained from these data definitely confirms the SNR nature of Hoinga. We also analysed INTEGRAL SPI data for fingerprints of 44 Ti emission, which is an ideal candidate with which to study nucleosynthesis imprinting in young SNRs. Although no 44 Ti emission from Hoinga was detected, we were able to set a 3 σ upper flux limit of 9.2 × 10 −5 ph cm −2 s −1 . From its size and X-ray and radio spectral properties we conclude that Hoinga is a middle-aged Vela-like SNR located at a distance of about twice that of the Vela SNR, i.e. at ~500 pc.
Discovery of a pulsar-powered bow shock nebula in the Small Magellanic Cloud supernova remnant DEM S5
Publisher: Oxford University Press (OUP)
Date: 08-04-2019
DOI: 10.1093/MNRAS/STZ971
A study of halo and relic radio emission in merging clusters using the Murchison Widefield Array
Publisher: Oxford University Press (OUP)
Date: 19-01-2017
DOI: 10.1093/MNRAS/STX155
Quantifying ionospheric effects on time-domain astrophysics with the Murchison Widefield Array
Publisher: Oxford University Press (OUP)
Date: 02-09-2015
Long-period Pulsars as Possible Outcomes of Supernova Fallback Accretion
Publisher: American Astronomical Society
Date: 08-2022
Abstract: For about half a century, the radio pulsar population was observed to spin in the ∼0.002–12 s range, with different pulsar classes having a spin-period evolution that differs substantially depending on their magnetic fields or past accretion history. The recent detection of several slowly rotating pulsars has reopened the long-standing question of the exact physics, and observational biases, driving the upper bound of the period range of the pulsar population. In this work, we perform a parameter study of the spin-period evolution of pulsars interacting with supernova fallback matter and specifically look at the fallback accretion disk scenario. Depending on the initial conditions at formation, this evolution can differ substantially from the typical dipolar spin-down, resulting in pulsars that show spin periods longer than their coeval peers. By using general assumptions for the pulsar spin period and magnetic field at birth, initial fallback accretion rates, and including magnetic field decay, we find that very long spin periods (≳100 s) can be reached in the presence of strong, magnetar-like magnetic fields (≳10 14 G) and moderate initial fallback accretion rates (∼10 22 −10 27 g s −1 ). In addition, we study the cases of two recently discovered periodic radio sources, the pulsar PSR J0901–4046 ( P = 75.9 s) and the radio transient GLEAM-X J162759.5–523504.3 ( P = 1091 s), in light of our model. We conclude that the supernova fallback scenario could represent a viable channel to produce a population of long-period isolated pulsars that only recent observation c aigns are starting to unveil.
Antenna array characterization via radio interferometry observation of astronomical sources
Publisher: IEEE
Date: 11-2014
Forging a sustainable future for astronomy
Publisher: Springer Science and Business Media LLC
Date: 15-09-2021
LOW-FREQUENCY OBSERVATIONS OF LINEARLY POLARIZED STRUCTURES IN THE INTERSTELLAR MEDIUM NEAR THE SOUTH GALACTIC POLE
Publisher: American Astronomical Society
Date: 10-10-2016
The Murchison Widefield Array Commissioning Survey: A Low-Frequency Catalogue of 14 110 Compact Radio Sources over 6 100 Square Degrees
Publisher: Cambridge University Press (CUP)
Date: 2014
DOI: 10.1017/PASA.2014.40
Abstract: We present the results of an approximately 6 100 deg 2 104–196 MHz radio sky survey performed with the Murchison Widefield Array during instrument commissioning between 2012 September and 2012 December: the MWACS. The data were taken as meridian drift scans with two different 32-antenna sub-arrays that were available during the commissioning period. The survey covers approximately 20.5 h RA 8.5 h, − 58° Dec −14°over three frequency bands centred on 119, 150 and 180 MHz, with image resolutions of 6–3 arcmin. The catalogue has 3 arcmin angular resolution and a typical noise level of 40 mJy beam − 1 , with reduced sensitivity near the field boundaries and bright sources. We describe the data reduction strategy, based upon mosaicked snapshots, flux density calibration, and source-finding method. We present a catalogue of flux density and spectral index measurements for 14 110 sources, extracted from the mosaic, 1 247 of which are sub-components of complexes of sources.
Extragalactic Peaked-spectrum Radio Sources at Low Frequencies
Publisher: American Astronomical Society
Date: 17-02-2017
CONFIRMATION OF WIDE-FIELD SIGNATURES IN REDSHIFTED 21 cm POWER SPECTRA
Publisher: American Astronomical Society
Date: 10-07-2015
A radio transient with unusually slow periodic emission
Publisher: Springer Science and Business Media LLC
Date: 26-01-2022
DOI: 10.1038/S41586-021-04272-X
Abstract: The high-frequency radio sky is bursting with synchrotron transients from massive stellar explosions and accretion events, but the low-frequency radio sky has, so far, been quiet beyond the Galactic pulsar population and the long-term scintillation of active galactic nuclei. The low-frequency band, however, is sensitive to exotic coherent and polarized radio-emission processes, such as electron-cyclotron maser emission from flaring M dwarfs
The Murchison Widefield Array Transients Survey (MWATS). A search for low frequency variability in a bright Southern hemisphere sample
Publisher: Oxford University Press (OUP)
Date: 18-10-2018
G64.5+0.9: a new shell supernova remnant with unusual central emission
Publisher: Oxford University Press (OUP)
Date: 09-2009
A Southern-Sky Total Intensity Source Catalogue at 2.3 GHz from S-Band Polarisation All-Sky Survey Data
Publisher: Cambridge University Press (CUP)
Date: 2017
DOI: 10.1017/PASA.2017.5
Abstract: The S -band Polarisation All-Sky Survey has observed the entire southern sky using the 64-m Parkes radio telescope at 2.3 GHz with an effective bandwidth of 184 MHz. The surveyed sky area covers all declinations δ ⩽ 0°. To analyse compact sources, the survey data have been re-processed to produce a set of 107 Stokes I maps with 10.75 arcmin resolution and the large scale emission contribution filtered out. In this paper, we use these Stokes I images to create a total intensity southern-sky extragalactic source catalogue at 2.3 GHz. The source catalogue contains 23 389 sources and covers a sky area of 16 600 deg 2 , excluding the Galactic plane for latitudes | b | 10°. Approximately, 8% of catalogued sources are resolved. S -band Polarisation All-Sky Survey source positions are typically accurate to within 35 arcsec. At a flux density of 225 mJy, the S -band Polarisation All-Sky Survey source catalogue is more than 95% complete, and ~ 94% of S -band Polarisation All-Sky Survey sources brighter than 500 mJy beam −1 have a counterpart at lower frequencies.
Microwave observations of spinning dust emission in NGC6946⋆
Publisher: Oxford University Press (OUP)
Date: 07-2010
DOI: 10.1111/J.1745-3933.2010.00878.X
Abstract: We report new cm-wave measurements at five frequencies between 15 and 18GHz of the continuum emission from the reportedly anomalous ‘region 4’ of the nearby galaxy NGC6946. We find that the emission in this frequency range is significantly in excess of that measured at 8.5GHz, but has a spectrum from 15 to 18GHz consistent with optically thin free–free emission from an ultracompact Hii region. In combination with previously published data, we fit four emission models containing different continuum components using the Bayesian spectrum analysis package radiospec. These fits show that, in combination with data at other frequencies, a model with a spinning dust component is slightly preferred to those that possess better-established emission mechanisms.
A joint analysis of AMI and CARMA observations of the recently discovered SZ galaxy cluster system AMI-CL J0300+2613
Publisher: Oxford University Press (OUP)
Date: 14-06-2013
DOI: 10.1093/MNRAS/STT873
Sunyaev-Zel’dovich observation of the Bullet-like cluster Abell 2146 with the Arcminute Microkelvin Imager★
Publisher: Oxford University Press (OUP)
Date: 09-05-2011
Parametrizing Epoch of Reionization foregrounds: a deep survey of low-frequency point-source spectra with the Murchison Widefield Array
Publisher: Oxford University Press (OUP)
Date: 11-02-2016
DOI: 10.1093/MNRAS/STW310
Ionospheric Modelling using GPS to Calibrate the MWA. I: Comparison of First Order Ionospheric Effects between GPS Models and MWA Observations
Publisher: Cambridge University Press (CUP)
Date: 2015
DOI: 10.1017/PASA.2015.29
Abstract: We compare first-order (refractive) ionospheric effects seen by the MWA with the ionosphere as inferred from GPS data. The first-order ionosphere manifests itself as a bulk position shift of the observed sources across an MWA field of view. These effects can be computed from global ionosphere maps provided by GPS analysis centres, namely the CODE. However, for precision radio astronomy applications, data from local GPS networks needs to be incorporated into ionospheric modelling. For GPS observations, the ionospheric parameters are biased by GPS receiver instrument delays, among other effects, also known as receiver DCBs. The receiver DCBs need to be estimated for any non-CODE GPS station used for ionosphere modelling. In this work, single GPS station-based ionospheric modelling is performed at a time resolution of 10 min. Also the receiver DCBs are estimated for selected Geoscience Australia GPS receivers, located at Murchison Radio Observatory, Yarragadee, Mount Magnet and Wiluna. The ionospheric gradients estimated from GPS are compared with that inferred from MWA. The ionospheric gradients at all the GPS stations show a correlation with the gradients observed with the MWA. The ionosphere estimates obtained using GPS measurements show promise in terms of providing calibration information for the MWA.
Interactions between the Jet and Disk Wind in Nearby Radio-intermediate Quasar III Zw 2
Publisher: American Astronomical Society
Date: 02-2023
Abstract: Disk winds and jets are ubiquitous in active galactic nuclei (AGN), and how these two components interact remains an open question. We study the radio properties of the radio-intermediate quasar III Zw 2. We detect two jet knots, J1 and J2, on parsec scales that move at a mildly apparent superluminal speed of 1.35 c . Two γ -ray flares were detected in III Zw 2 in 2009–2010, corresponding to the primary radio flare in late 2009 and the secondary radio flare in early 2010. The primary 2009 flare was found to be associated with the ejection of J2. The secondary 2010 flare occurred at a distance of ∼0.3 pc from the central engine, probably resulting from the collision of the jet with the accretion disk wind. The variability characteristics of III Zw 2 (periodic radio flares, unstable periodicity, multiple quasiperiodic signals and the possible harmonic relations between them) can be explained by the global instabilities of the accretion disk. These instabilities originating from the outer part of the warped disk propagate inward and can lead to modulation of the accretion rate and consequent jet ejection. At the same time, the wobbling of the outer disk may also lead to oscillations of the boundary between the disk wind and the jet tunnel, resulting in changes in the jet–wind collision site. Object III Zw 2 is one of the few cases observed with jet–wind interactions, and the study in this paper is of general interest for gaining insight into the dynamic processes in the nuclear regions of AGN.
MURCHISON WIDEFIELD ARRAY OBSERVATIONS OF ANOMALOUS VARIABILITY: A SERENDIPITOUS NIGHT-TIME DETECTION OF INTERPLANETARY SCINTILLATION
Publisher: American Astronomical Society
Date: 07-08-2015
GLEAM: The GaLactic and Extragalactic All-Sky MWA Survey
Publisher: Cambridge University Press (CUP)
Date: 2015
DOI: 10.1017/PASA.2015.26
Abstract: GLEAM, the GaLactic and Extragalactic All-sky MWA survey, is a survey of the entire radio sky south of declination + 25° at frequencies between 72 and 231 MHz, made with the MWA using a drift scan method that makes efficient use of the MWA’s very large field-of-view. We present the observation details, imaging strategies, and theoretical sensitivity for GLEAM. The survey ran for two years, the first year using 40-kHz frequency resolution and 0.5-s time resolution the second year using 10-kHz frequency resolution and 2 s time resolution. The resulting image resolution and sensitivity depends on observing frequency, sky pointing, and image weighting scheme. At 154 MHz, the image resolution is approximately 2.5 × 2.2/cos (δ + 26.7°) arcmin with sensitivity to structures up to ~ 10° in angular size. We provide tables to calculate the expected thermal noise for GLEAM mosaics depending on pointing and frequency and discuss limitations to achieving theoretical noise in Stokes I images. We discuss challenges, and their solutions, that arise for GLEAM including ionospheric effects on source positions and linearly polarised emission, and the instrumental polarisation effects inherent to the MWA’s primary beam.
A blind detection of a large, complex, Sunyaev-Zel’dovich structure★
Publisher: Oxford University Press (OUP)
Date: 02-05-2012
Low-Frequency Carbon Recombination Lines in the Orion Molecular Cloud Complex
Publisher: Cambridge University Press (CUP)
Date: 2018
DOI: 10.1017/PASA.2018.13
Abstract: We detail tentative detections of low-frequency carbon radio recombination lines from within the Orion molecular cloud complex observed at 99–129 MHz. These tentative detections include one alpha transition and one beta transition over three locations and are located within the diffuse regions of dust observed in the infrared at 100 μm, the Hα emission detected in the optical, and the synchrotron radiation observed in the radio. With these observations, we are able to study the radiation mechanism transition from collisionally pumped to radiatively pumped within the H ii regions within the Orion molecular cloud complex.
A Molecular Line Survey around Orion at Low Frequencies with the MWA
Publisher: American Astronomical Society
Date: 21-06-2018
Spectral variability of radio sources at low frequencies
Publisher: Oxford University Press (OUP)
Date: 11-12-2020
Abstract: Spectral variability of radio sources encodes information about the conditions of intervening media, source structure, and emission processes. With new low-frequency radio interferometers observing over wide fractional bandwidths, studies of spectral variability for a large population of extragalactic radio sources are now possible. Using two epochs of observations from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey that were taken one year apart, we search for spectral variability across 100–230 MHz for 21 558 sources. We present methodologies for detecting variability in the spectrum between epochs and for classifying the type of variability: either as a change in spectral shape or as a uniform change in flux density across the bandwidth. We identify 323 sources with significant spectral variability over a year-long time-scale. Of the 323 variable sources, we classify 51 of these as showing a significant change in spectral shape. Variability is more prevalent in peaked-spectrum sources, analogous to gigahertz-peaked spectrum and compact steep-spectrum sources, compared to typical radio galaxies. We discuss the viability of several potential explanations of the observed spectral variability, such as interstellar scintillation and jet evolution. Our results suggest that the radio sky in the megahertz regime is more dynamic than previously suggested.
The jet/wind outflow in Centaurus A: A local laboratory for AGN feedback
Publisher: Oxford University Press (OUP)
Date: 09-11-2018
Wide-band spectral variability of peaked spectrum sources
Publisher: Oxford University Press (OUP)
Date: 26-03-2022
Abstract: Characterizing spectral variability of radio sources is a technique that offers the ability to determine the astrophysics of the intervening media, source structure, emission, and absorption processes. We present broadband (0.072–10 GHz) spectral variability of 15 peaked-spectrum (PS) sources with the Australia Telescope Compact Array (ATCA) and the Murchison Widefield Array (MWA). These 15 PS sources were observed quasi-contemporaneously with ATCA and the MWA four to six times during 2020 with approximately a monthly cadence. Variability was not detected at 1–10 GHz frequencies but 13 of the 15 targets show significant variability with the MWA at megahertz frequencies. We conclude the majority of variability seen at megahertz frequencies is due to refractive interstellar scintillation of a compact component ∼25 mas across. We also identify four PS sources that show a change in their spectral shape at megahertz frequencies. Three of these sources are consistent with a variable optical depth from an inhomogeneous free–free absorbing cloud around the source. One PS source with a variable spectral shape at megahertz frequencies is consistent with an ejection travelling along the jet. We present spectral variability as a method for determining the physical origins of observed variability and for providing further evidence to support absorption models for PS sources where spectral modelling alone is insufficient.
Bayesian analysis of weak gravitational lensing and Sunyaev-Zel’dovich data for six galaxy clusters★
Publisher: Oxford University Press (OUP)
Date: 15-12-2011
Milliarcsecond structures of variable-peaked spectrum sources
Publisher: Cambridge University Press (CUP)
Date: 2023
DOI: 10.1017/PASA.2023.1
Abstract: Spectral variability offers a new technique to identify small scale structures from scintillation, as well as determining the absorption mechanism for peaked-spectrum (PS) radio sources. In this paper, we present very long baseline interferometry (VLBI) imaging using the long baseline array (LBA) of two PS sources, MRC 0225–065 and PMN J0322–4820, identified as spectrally variable from observations with the Murchison Widefield Array (MWA). We compare expected milliarcsecond structures based on the detected spectral variability with direct LBA imaging. We find MRC 0225–065 is resolved into three components, a bright core and two fainter lobes, roughly 430 pc projected separation. A comprehensive analysis of the magnetic field, host galaxy properties, and spectral analysis implies that MRC 0225–065 is a young radio source with recent jet activity over the last $10^2$ – $10^3$ yr. We find PMN J0322–4820 is unresolved on milliarcsecond scales. We conclude PMN J0322–4820 is a blazar with flaring activity detected in 2014 with the MWA. We use spectral variability to predict morphology and find these predictions consistent with the structures revealed by our LBA images.
DELAY SPECTRUM WITH PHASE-TRACKING ARRAYS: EXTRACTING THE H i POWER SPECTRUM FROM THE EPOCH OF REIONIZATION
Publisher: American Astronomical Society
Date: 19-12-2016
Remnant radio galaxies discovered in a multi-frequency survey
Publisher: Cambridge University Press (CUP)
Date: 2021
DOI: 10.1017/PASA.2020.49
Abstract: The remnant phase of a radio galaxy begins when the jets launched from an active galactic nucleus are switched off. To study the fraction of radio galaxies in a remnant phase, we take advantage of a $8.31$ deg $^2$ subregion of the GAMA 23 field which comprises of surveys covering the frequency range 0.1–9 GHz. We present a s le of 104 radio galaxies compiled from observations conducted by the Murchison Widefield Array (216 MHz), the Australia Square Kilometer Array Pathfinder (887 MHz), and the Australia Telescope Compact Array (5.5 GHz). We adopt an ‘absent radio core’ criterion to identify 10 radio galaxies showing no evidence for an active nucleus. We classify these as new candidate remnant radio galaxies. Seven of these objects still display compact emitting regions within the lobes at 5.5 GHz at this frequency the emission is short-lived, implying a recent jet switch off. On the other hand, only three show evidence of aged lobe plasma by the presence of an ultra-steep-spectrum ( $\\alpha -1.2$ ) and a diffuse, low surface brightness radio morphology. The predominant fraction of young remnants is consistent with a rapid fading during the remnant phase. Within our s le of radio galaxies, our observations constrain the remnant fraction to $4\\%\\lesssim f_{\\mathrm{rem}} \\lesssim 10\\%$ the lower limit comes from the limiting case in which all remnant candidates with hotspots are simply active radio galaxies with faint, undetected radio cores. Finally, we model the synchrotron spectrum arising from a hotspot to show they can persist for 5–10 Myr at 5.5 GHz after the jets switch of—radio emission arising from such hotspots can therefore be expected in an appreciable fraction of genuine remnants.
Murchison Widefield Array rapid-response observations of the short GRB 180805A
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.
The Relativistic Jet-accretion Flow–wind Connection in Mrk 231
Publisher: American Astronomical Society
Date: 16-02-2017
Calibration and Stokes Imaging with Full Embedded Element Primary Beam Model for the Murchison Widefield Array
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.
An analysis of the halo and relic radio emission from Abell 3376 from Murchison Widefield Array observations
Publisher: Oxford University Press (OUP)
Date: 30-06-2015
A Supernova Remnant Counterpart for HESS J1832−085
Publisher: American Astronomical Society
Date: 07-11-2019
AMI observations of Lynds dark nebulae: further evidence for anomalous cm-wave emission
Publisher: Oxford University Press (OUP)
Date: 11-12-2009
AMI SZ observations and Bayesian analysis of a sample of six redshift-one clusters of galaxies
Publisher: Oxford University Press (OUP)
Date: 05-03-2013
DOI: 10.1093/MNRAS/STT212
A new angle for probing field-aligned irregularities with the Murchison Widefield Array
Publisher: American Geophysical Union (AGU)
Date: 06-2016
DOI: 10.1002/2015RS005878
Murchison Widefield Array and XMM-Newton observations of the Galactic supernova remnant G5.9+3.1
Publisher: EDP Sciences
Date: 05-2019
DOI: 10.1051/0004-6361/201834230
Abstract: Aims. In this paper we discuss the radio continuum and X-ray properties of the so-far poorly studied Galactic supernova remnant (SNR) G5.9 + 3.1. Methods. We present the radio spectral energy distribution (SED) of the Galactic SNR G5.9 + 3.1 obtained with the Murchison Widefield Array (MWA). Combining these new observations with the surveys at other radio continuum frequencies, we discuss the integrated radio continuum spectrum of this particular remnant. We have also analyzed an archival XMM-Newton observation, which represents the first detection of X-ray emission from this remnant. Results. The SNR SED is very well explained by a simple power-law relation. The synchrotron radio spectral index of G5.9 + 3.1 is estimated to be 0.42 ± 0.03 and the integrated flux density at 1 GHz to be around 2.7 Jy. Furthermore, we propose that the identified point radio source, located centrally inside the SNR shell, is most probably a compact remnant of the supernova explosion. The shell-like X-ray morphology of G5.9 + 3.1 as revealed by XMM-Newton broadly matches the spatial distribution of the radio emission, where the radio-bright eastern and western rims are also readily detected in the X-ray while the radio-weak northern and southern rims are weak or absent in the X-ray. Extracted MOS1+MOS2+PN spectra from the whole SNR as well as the north, east, and west rims of the SNR are fit successfully with an optically thin thermal plasma model in collisional ionization equilibrium with a column density N H ~ 0.80 × 10 22 cm −2 and fitted temperatures spanning the range kT ~ 0.14–0.23 keV for all of the regions. The derived electron number densities n e for the whole SNR and the rims are also roughly comparable (ranging from ~0.20 f −1∕2 to ~0.40 f −1∕2 cm −3 , where f is the volume filling factor). We also estimate the swept-up mass of the X-ray emitting plasma associated with G5.9+3.1 to be ~46 f −1∕2 M ⊙ .
Characterization of a Low-Frequency Radio Astronomy Prototype Array in Western Australia
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 12-2015
Unexpected circular radio objects at high Galactic latitude
Publisher: Cambridge University Press (CUP)
Date: 2021
DOI: 10.1017/PASA.2020.52
Abstract: We have found a class of circular radio objects in the Evolutionary Map of the Universe Pilot Survey, using the Australian Square Kilometre Array Pathfinder telescope. The objects appear in radio images as circular edge-brightened discs, about one arcmin diameter, that are unlike other objects previously reported in the literature. We explore several possible mechanisms that might cause these objects, but none seems to be a compelling explanation.
The POlarised GLEAM Survey (POGS) I: First results from a low-frequency radio linear polarisation survey of the southern sky
Publisher: Cambridge University Press (CUP)
Date: 2018
DOI: 10.1017/PASA.2018.39
Abstract: The low-frequency polarisation properties of radio sources are poorly studied, particularly in statistical s les. However, the new generation of low-frequency telescopes, such as the Murchison Widefield Array (the precursor for the low-frequency component of the Square Kilometre Array) offers an opportunity to probe the physics of radio sources at very low radio frequencies. In this paper, we present a catalogue of linearly polarised sources detected at 216 MHz, using data from the Galactic and Extragalactic All-sky Murchison Widefield Array survey. Our catalogue covers the Declination range –17° to –37° and 24 h in Right Ascension, at a resolution of around 3 arcminutes. We detect 81 sources (including both a known pulsar and a new pulsar candidate) with linearly polarised flux densities in excess of 18 mJy across a survey area of approximately 6 400 deg 2 , corresponding to a surface density of 1 source per 79 deg 2 . The level of Faraday rotation measured for our sources is broadly consistent with those recovered at higher frequencies, with typically more than an order of magnitude improvement in the uncertainty compared to higher-frequency measurements. However, our catalogue is likely incomplete at low Faraday rotation measures, due to our practice of excluding sources in the region where instrumental leakage appears. The majority of sources exhibit significant depolarisation compared to higher frequencies however, a small sub-s le repolarise at 216 MHz. We also discuss the polarisation properties of four nearby, large-angular-scale radio galaxies, with a particular focus on the giant radio galaxy ESO 422–G028, in order to explain the striking differences in polarised morphology between 216 MHz and 1.4 GHz.
Long-wave (Radio) Astronomy with Coherent Detection from Radio to THz
Publisher: IOP Publishing
Date: 12-2021
A Large-Scale, Low-Frequency Murchison Widefield Array Survey of Galactic H ii Regions between 260 < l < 340
Publisher: Cambridge University Press (CUP)
Date: 2016
DOI: 10.1017/PASA.2016.19
Abstract: We have compiled a catalogue of H ii regions detected with the Murchison Widefield Array between 72 and 231 MHz. The multiple frequency bands provided by the Murchison Widefield Array allow us identify the characteristic spectrum generated by the thermal Bremsstrahlung process in H ii regions. We detect 306 H ii regions between 260° l 340° and report on the positions, sizes, peak, integrated flux density, and spectral indices of these H ii regions. By identifying the point at which H ii regions transition from the optically thin to thick regime, we derive the physical properties including the electron density, ionised gas mass, and ionising photon flux, towards 61 H ii regions. This catalogue of H ii regions represents the most extensive and uniform low frequency survey of H ii regions in the Galaxy to date.
GaLactic and Extragalactic All-sky Murchison Widefield Array survey eXtended (GLEAM-X) I: Survey description and initial data release
Publisher: Cambridge University Press (CUP)
Date: 2022
DOI: 10.1017/PASA.2022.17
Abstract: We describe a new low-frequency wideband radio survey of the southern sky. Observations covering 72–231 MHz and Declinations south of $+30^\\circ$ have been performed with the Murchison Widefield Array “extended” Phase II configuration over 2018–2020 and will be processed to form data products including continuum and polarisation images and mosaics, multi-frequency catalogues, transient search data, and ionospheric measurements. From a pilot field described in this work, we publish an initial data release covering 1,447 $\\mathrm{deg}^2$ over $4\\,\\mathrm{h}\\leq \\mathrm{RA}\\leq 13\\,\\mathrm{h}$ , $-32.7^\\circ \\leq \\mathrm{Dec} \\leq -20.7^\\circ$ . We process twenty frequency bands s ling 72–231 MHz, with a resolution of 2′–45 ′′ , and produce a wideband source-finding image across 170–231 MHz with a root mean square noise of $1.27\\pm0.15\\,\\mathrm{mJy\\,beam}^{-1}$ . Source-finding yields 78,967 components, of which 71,320 are fitted spectrally. The catalogue has a completeness of 98% at ${{\\sim}}50\\,\\mathrm{mJy}$ , and a reliability of 98.2% at $5\\sigma$ rising to 99.7% at $7\\sigma$ . A catalogue is available from Vizier images are made available via the PASA datastore, AAO Data Central, and SkyView. This is the first in a series of data releases from the GLEAM-X survey.
Selecting and modelling remnant AGNs with limited spectral coverage
Publisher: Oxford University Press (OUP)
Date: 18-05-2022
Abstract: Quantifying the energetics and lifetimes of remnant radio-loud active galactic nuclei (AGNs) is much more challenging than for active sources due to the added complexity of accurately determining the time since the central black hole switched off. Independent spectral modelling of remnant lobes enables the derivation of the remnant ratio, Rrem (i.e. ‘off-time/source age’) however, the requirement of high-frequency (≳5 GHz) coverage makes the application of this technique over large-area radio surveys difficult. In this work, we propose a new method, which relies on the observed brightness of backflow of Fanaroff–Riley type II lobes, combined with the Radio AGN in Semi-Analytic Environments (RAiSE) code, to measure the duration of the remnant phase. Sensitive radio observations of the remnant radio galaxy J2253-34 are obtained to provide a robust comparison of this technique with the canonical spectral analysis and modelling methods. We find that the remnant lifetimes modelled by each method are consistent spectral modelling yields Rrem = 0.23 ± 0.02, compared to Rrem = 0.26 ± 0.02 from our new method. We examine the viability of applying our proposed technique to low-frequency radio surveys using mock radio source populations, and examine whether the technique is sensitive to any intrinsic properties of radio AGNs. Our results show that the technique can be used to robustly classify active and remnant populations, with the most confident predictions for the remnant ratio, and thus off-time, in the longest lived radio sources (& Myr) and those at higher redshifts (z & 0.1).
Sunyaev-Zel’dovich observations of galaxy clusters out to the virial radius with the Arcminute Microkelvin Imager★
Publisher: Oxford University Press (OUP)
Date: 22-11-2011
Assessing Risks and Opportunities Arising from Ecosystem Change in Primary Industries Using Ecosystem-Based Business Risk Analysis Tool
Publisher: Informa UK Limited
Date: 2012
Dark matter annihilation in ω Centauri: Astrophysical implications derived from the MWA radio data
Publisher: Elsevier BV
Date: 12-2020
AMI radio continuum observations of young stellar objects with known outflows★
Publisher: Oxford University Press (OUP)
Date: 21-05-2012
Constraining the Nature of the 18 min Periodic Radio Transient GLEAM-X J162759.5-523504.3 via Multiwavelength Observations and Magneto-thermal Simulations
Publisher: American Astronomical Society
Date: 11-2022
Abstract: We observed the periodic radio transient GLEAM-X J162759.5-523504.3 (GLEAM-X J1627) using the Chandra X-ray Observatory for about 30 ks on 2022 January 22–23, simultaneously with radio observations from the Murchison Widefield Array, MeerKAT, and the Australia Telescope Compact Array. Its radio emission and 18 min periodicity led the source to be tentatively interpreted as an extreme magnetar or a peculiar highly magnetic white dwarf. The source was not detected in the 0.3–8 keV energy range with a 3 σ upper limit on the count rate of 3 × 10 −4 counts s −1 . No radio emission was detected during our X-ray observations either. Furthermore, we studied the field around GLEAM-X J1627 using archival European Southern Observatory and DECam Plane Survey data, as well as recent Southern African Large Telescope observations. Many sources are present close to the position of GLEAM-X J1627, but only two within the 2″ radio position uncertainty. Depending on the assumed spectral distribution, the upper limits converted to an X-ray luminosity of L X 6.5 × 10 29 erg s −1 for a blackbody with temperature kT = 0.3 keV, or L X 9 × 10 29 erg s −1 for a power law with photon index Γ = 2 (assuming a 1.3 kpc distance). Furthermore, we performed magneto-thermal simulations for neutron stars considering crust- and core-dominated field configurations. Based on our multiband limits, we conclude that (i) in the magnetar scenario, the X-ray upper limits suggest that GLEAM-X J1627 should be older than ∼1 Myr, unless it has a core-dominated magnetic field or has experienced fast cooling (ii) in the white dwarf scenario, we can rule out most binary systems, a hot sub-dwarf, and a hot magnetic isolated white dwarf ( T ≳ 10.000 K), while a cold isolated white dwarf is still compatible with our limits.
Searching for the synchrotron cosmic web again: A replication attempt
Publisher: Cambridge University Press (CUP)
Date: 2022
DOI: 10.1017/PASA.2022.9
Abstract: We follow up on the surprising recent announcement by Vernstrom et al. (2021, MNRAS) of the detection of the synchrotron cosmic web. We attempt to reproduce their detection with new observations with the Phase II, extended configuration of the Murchison Widefield Array at 118.5 MHz. We reproduce their detection methodology by stacking pairs of nearby luminous red galaxies (LRGs)—used as tracers for clusters and galaxy groups—contained in our low-frequency radio observations. We show that our observations are significantly more sensitive than those used in Vernstrom et al. and that our angular sensitivity is sufficient. And yet, we make no statistically significant detection of excess radio emission along the bridge spanning the LRG pairs. This non-detection is true both for the original LRG pair catalogue as used in Vernstrom et al., as well as for other larger catalogues with modified selection criteria. Finally, we return to the original data sets used in Vernstrom et al., and find that whilst we clearly reproduce the excess X-ray emission from ROSAT, we are not able to reproduce any kind of broad and extended excess intercluster filamentary emission using the original 118.5 MHz MWA survey data. In the interests of understanding this result, as part of this paper we release images of the 14 fields used in this study, the final stacked images, as well as key components of our stacking and modelling code.
Measuring the global 21-cm signal with the MWA-I: improved measurements of the Galactic synchrotron background using lunar occultation
Publisher: Oxford University Press (OUP)
Date: 06-09-2018
Parametrization effects in the analysis of AMI Sunyaev-Zel’dovich observations★
Publisher: Oxford University Press (OUP)
Date: 30-01-2012
Ionospheric Irregularities Observed During the GLEAM Survey
Publisher: American Geophysical Union (AGU)
Date: 10-2020
DOI: 10.1029/2020RS007106
Discovery of a radio transient in M81
Publisher: Oxford University Press (OUP)
Date: 14-05-2019
Abstract: We report the discovery of a radio transient in the spiral galaxy M81. The transient was detected in early 2015 as part of a two-year survey of M81 made up of 12 epochs using the Karl G. Jansky Very Large Array. While undetected on 2014 September 12, the source was first detected on 2015 January 2, from which point it remained visible at an approximately constant luminosity of LR, ν = 1.5 ± 0.1 × 1024 erg s−1 Hz−1 at the observing frequency of 6 GHz for at least 2 months. Assuming this is a synchrotron event with a rise-time between 2.6 and 112 d, the peak luminosity (at equipartition) corresponds to a minimum energy of 1044 ≲ Emin ≲ 1046 erg and jet power of Pmin ∼ 1039 erg s−1, which are higher than most known X-ray binaries. Given its longevity, lack of short-term radio variability, and the absence of any multiwavelength counterpart (X-ray luminosity Lx ≲ 1036 erg s−1), it does not behave like known Galactic or extragalactic X-ray binaries. The M81 transient radio properties more closely resemble the unidentified radio transient 43.78+59.3 discovered in M82, which has been suggested to be a radio nebula associated with an accreting source similar to SS 433. One possibility is that both the new M81 transient and the M82 transient may be the birth of a short-lived radio bubble associated with a discrete accretion event similar to those observed from the ULX Holmberg II X-1. However, it is not possible to rule out other identifications including long-term supernova shockwave interactions with the surrounding medium from a faint supernova or a background active galaxy.
AMI limits on 15-GHz excess emission in northern H ii regions
Publisher: Oxford University Press (OUP)
Date: 04-2008
High-resolution Observations of Low-luminosity Gigahertz-Peaked Spectrum and Compact Steep Spectrum Sources
Publisher: Oxford University Press (OUP)
Date: 03-03-2018
DOI: 10.1093/MNRAS/STY564
A broadband radio view of transient jet ejecta in the black hole candidate X-ray binary MAXI J1535–571
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.
A long-period radio transient active for three decades
Publisher: Springer Science and Business Media LLC
Date: 19-07-2023
Erratum: Galactic synchrotron emissivity measurements between 250° < l < 355° from the GLEAM survey with the MWA
Publisher: Oxford University Press (OUP)
Date: 17-08-2017
The GLEAM 200-MHz local radio luminosity function for AGN and star-forming galaxies
Publisher: Cambridge University Press (CUP)
Date: 2021
DOI: 10.1017/PASA.2021.36
Abstract: The GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) is a radio continuum survey at 76–227 MHz of the entire southern sky (Declination $ \\!{+}30^{\\circ}$ ) with an angular resolution of ${\\approx}2$ arcmin. In this paper, we combine GLEAM data with optical spectroscopy from the 6dF Galaxy Survey to construct a s le of 1 590 local (median $z \\approx 0.064$ ) radio sources with $S_{200\\,\\mathrm{MHz}} 55$ mJy across an area of ${\\approx}16\\,700\\,\\mathrm{deg}^{2}$ . From the optical spectra, we identify the dominant physical process responsible for the radio emission from each galaxy: 73% are fuelled by an active galactic nucleus (AGN) and 27% by star formation. We present the local radio luminosity function for AGN and star-forming (SF) galaxies at 200 MHz and characterise the typical radio spectra of these two populations between 76 MHz and ${\\sim}1$ GHz. For the AGN, the median spectral index between 200 MHz and ${\\sim}1$ GHz, $\\alpha_{\\mathrm{high}}$ , is $-0.600 \\pm 0.010$ (where $S \\propto \\nu^{\\alpha}$ ) and the median spectral index within the GLEAM band, $\\alpha_{\\mathrm{low}}$ , is $-0.704 \\pm 0.011$ . For the SF galaxies, the median value of $\\alpha_{\\mathrm{high}}$ is $-0.650 \\pm 0.010$ and the median value of $\\alpha_{\\mathrm{low}}$ is $-0.596 \\pm 0.015$ . Among the AGN population, flat-spectrum sources are more common at lower radio luminosity, suggesting the existence of a significant population of weak radio AGN that remain core-dominated even at low frequencies. However, around 4% of local radio AGN have ultra-steep radio spectra at low frequencies ( $\\alpha_{\\mathrm{low}} -1.2$ ). These ultra-steep-spectrum sources span a wide range in radio luminosity, and further work is needed to clarify their nature.
A high reliability survey of discrete Epoch of Reionization foreground sources in the MWA EoR0 field
Publisher: Oxford University Press (OUP)
Date: 08-07-2016
Mysterious odd radio circle near the large magellanic cloud – an intergalactic supernova remnant?
Publisher: Oxford University Press (OUP)
Date: 04-02-2022
Abstract: We report the discovery of J0624–6948, a low-surface brightness radio ring, lying between the Galactic Plane and the large magellanic cloud (LMC). It was first detected at 888 MHz with the Australian Square Kilometre Array Pathfinder (ASKAP), and with a diameter of ∼196 arcsec. This source has phenomenological similarities to odd radio circles (ORCs). Significant differences to the known ORCs – a flatter radio spectral index, the lack of a prominent central galaxy as a possible host, and larger apparent size – suggest that J0624–6948 may be a different type of object. We argue that the most plausible explanation for J0624–6948 is an intergalactic supernova remnant due to a star that resided in the LMC outskirts that had undergone a single-degenerate type Ia supernova, and we are seeing its remnant expand into a rarefied, intergalactic environment. We also examine if a massive star or a white dwarf binary ejected from either galaxy could be the supernova progenitor. Finally, we consider several other hypotheses for the nature of the object, including the jets of an active galactic nucleus (30Dor) or the remnant of a nearby stellar super-flare.
Robbie: A batch processing work-flow for the detection of radio transients and variables
Publisher: Elsevier BV
Date: 04-2019
A magnetar parallax
Publisher: Oxford University Press (OUP)
Date: 21-08-2020
Abstract: XTE J1810−197 (J1810) was the first magnetar identified to emit radio pulses, and has been extensively studied during a radio-bright phase in 2003–2008. It is estimated to be relatively nearby compared to other Galactic magnetars, and provides a useful prototype for the physics of high magnetic fields, magnetar velocities, and the plausible connection to extragalactic fast radio bursts. Upon the rebrightening of the magnetar at radio wavelengths in late 2018, we resumed an astrometric c aign on J1810 with the Very Long Baseline Array, and s led 14 new positions of J1810 over 1.3 yr. The phase calibration for the new observations was performed with two-phase calibrators that are quasi-colinear on the sky with J1810, enabling substantial improvement of the resultant astrometric precision. Combining our new observations with two archival observations from 2006, we have refined the proper motion and reference position of the magnetar and have measured its annual geometric parallax, the first such measurement for a magnetar. The parallax of 0.40 ± 0.05 mas corresponds to a most probable distance $2.5^{\\, +0.4}_{\\, -0.3}$ kpc for J1810. Our new astrometric results confirm an unremarkable transverse peculiar velocity of ≈200 $\\rm km~s^{-1}$ for J1810, which is only at the average level among the pulsar population. The magnetar proper motion vector points back to the central region of a supernova remnant (SNR) at a compatible distance at ≈70 kyr ago, but a direct association is disfavoured by the estimated SNR age of ∼3 kyr.
Spectral Energy Distribution and Radio Halo of NGC 253 at Low Radio Frequencies
Publisher: American Astronomical Society
Date: 27-03-2017
One unit to rule them all
Publisher: Springer Science and Business Media LLC
Date: 07-2021
Investigating the source of planck-detected AME: High-resolution observations at 15 GHz
Publisher: Hindawi Limited
Date: 2013
DOI: 10.1155/2013/354259
Abstract: The Planck 28.5 GHz maps were searched for potential Anomalous Microwave Emission (AME) regions on the scale of ~ 3° or smaller, and several new regions of interest were selected. Ancillary data at both lower and higher frequencies were used to construct spectral energy distributions (SEDs), which seem to confirm an excess consistent with spinning dust models. Here we present higher resolution observations of two of these new regions with the Arcminute Microkelvin Imager Small Array (AMI SA) between 14 and 18 GHz to test for the presence of a compact ( ~ 10 arcmin or smaller) component. For AME-G107.1+5.2, dominated by the Hii region S140, we find evidence for the characteristic rising spectrum associated with either the spinning dust mechanism for AME or an ultra- /hypercompact Hii region across the AMI frequency band however, for AME-G173.6+208 we find no evidence for AME on scales of ~ 2–10 arcmin.
The Murchison Widefield Array Correlator
Publisher: Cambridge University Press (CUP)
Date: 2015
DOI: 10.1017/PASA.2015.5
Abstract: The Murchison Widefield Array is a Square Kilometre Array Precursor. The telescope is located at the Murchison Radio–astronomy Observatory in Western Australia. The MWA consists of 4 096 dipoles arranged into 128 dual polarisation aperture arrays forming a connected element interferometer that cross-correlates signals from all 256 inputs. A hybrid approach to the correlation task is employed, with some processing stages being performed by bespoke hardware, based on Field Programmable Gate Arrays, and others by Graphics Processing Units housed in general purpose rack mounted servers. The correlation capability required is approximately 8 tera floating point operations per second. The MWA has commenced operations and the correlator is generating 8.3 TB day −1 of correlation products, that are subsequently transferred 700 km from the MRO to Perth (WA) in real-time for storage and offline processing. In this paper, we outline the correlator design, signal path, and processing elements and present the data format for the internal and external interfaces.
The radio spectral energy distribution of infrared-faint radio sources
Publisher: EDP Sciences
Date: 09-2016
AMI galactic plane survey at 16 GHz - II. Full data release with extended coverage and improved processing
Publisher: Oxford University Press (OUP)
Date: 25-08-2015
AMI Galactic Plane Survey at 16 GHz - I. Observing, mapping and source extraction
Publisher: Oxford University Press (OUP)
Date: 16-01-2013
DOI: 10.1093/MNRAS/STS589
A first look for molecules between 103 and 133 MHz using the Murchison Widefield Array
Publisher: Oxford University Press (OUP)
Date: 20-07-2017
Related Organisations
University Of Cambridge
Location: United Kingdom of Great Britain and Northern Ireland
University Of Bristol
Location: United Kingdom of Great Britain and Northern Ireland
Related Funding Activities
EXtending The GLEAM View Of The Universe
Start Date: 2019
End Date: 2022
Funder: Australian Research Council
View Funded ActivityARC Future Fellowships - Grant ID: FT190100231
Start Date: 2020
End Date: 12-2024
Amount: $857,533.00
Funder: Australian Research Council
View Funded ActivitySuper Science Fellowships - Grant ID: FS110200003
Start Date: 08-2011
End Date: 07-2014
Amount: $278,400.00
Funder: Australian Research Council
View Funded ActivityLinkage Infrastructure, Equipment And Facilities - Grant ID: LE210100015
Start Date: 11-2021
End Date: 10-2025
Amount: $1,680,000.00
Funder: Australian Research Council
View Funded Activity