Dougal Dobie

University of Sydney

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Tara Murphy

University of Sydney

D. L. Kaplan

University of Wisconsin–Milwaukee

E. Lenc

Australia Telescope National Facility

M. M. Kasliwal

California Institute of Technology

K. W. Bannister

Commonwealth Scientific and Industrial Research Organisation

David E. Kaplan

Johns Hopkins University

A. Stewart

University of Sydney

C. Lynch

University of North Carolina at Asheville

Ziteng Wang

International Centre for Radio Astronomy Research

Igor Andreoni

Joint Space Science Institute

Cooperative Institutions

Centre National de la Recherche Scientifique

625

California Institute of Technology

429

Consejo Nacional de Investigaciones Científicas y Técnicas

285

Goddard Space Flight Center

249

Université Paris Cité

247

Chinese Academy of Sciences

234

ARC Centre of Excellence for Gravitational Wave Discovery

220

Max Planck Society

198

National Institute for Astrophysics

189

University of Alaska Anchorage

183

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A search for radio afterglows from gamma-ray bursts with the Australian Square Kilometre Array Pathfinder

Monthly Notices of the Royal Astronomical Society (2021)

James K. Leung Tara Murphy G. Ghirlanda D. L. Kaplan E. Lenc

We present a search for radio afterglows from long gamma-ray bursts using the Australian Square Kilometre Array Pathfinder (ASKAP). Our search used the Rapid ASKAP Continuum Survey, covering the entire celestial sphere south of declination $+41^\circ$, and three epochs of the Variables and Slow Transients Pilot Survey (Phase 1), covering $\sim 5,000$ square degrees per epoch. The observations we used from these surveys spanned a nine-month period from 2019 April 21 to 2020 January 11. We crossmatched radio sources found in these surveys with 779 well-localised (to $\leq 15''$) long gamma-ray bursts occurring after 2004 and determined whether the associations were more likely afterglow- or host-related through the analysis of optical images. In our search, we detected one radio afterglow candidate associated with GRB 171205A, a local low-luminosity gamma-ray burst with a supernova counterpart SN 2017iuk, in an ASKAP observation 511 days post-burst. We confirmed this detection with further observations of the radio afterglow using the Australia Telescope Compact Array at 859 days and 884 days post-burst. Combining this data with archival data from early-time radio observations, we showed the evolution of the radio spectral energy distribution alone could reveal clear signatures of a wind-like circumburst medium for the burst. Finally, we derived semi-analytical estimates for the microphysical shock parameters of the burst: electron power-law index $p = 2.84$, normalised wind-density parameter $A_* = 3$, fractional energy in electrons $\epsilon_{e} = 0.3$, and fractional energy in magnetic fields $\epsilon_{B} = 0.0002$.

10.1093/mnras/stab326

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An ASKAP Search for a Radio Counterpart to the First High-significance Neutron Star–Black Hole Merger LIGO/Virgo S190814bv

The Astrophysical Journal Letters (2019)

Dougal Dobie A. Stewart Tara Murphy E. Lenc Ziteng Wang

Abstract We present results from a search for a radio transient associated with the LIGO/Virgo source S190814bv, a likely neutron star–black hole (NSBH) merger, with the Australian Square Kilometre Array Pathfinder. We imaged a 30 deg 2 field at Δ T = 2, 9, and 33 days post-merger at a frequency of 944 MHz, comparing them to reference images from the Rapid ASKAP Continuum Survey observed 110 days prior to the event. Each epoch of our observations covers 89% of the LIGO/Virgo localization region. We conducted an untargeted search for radio transients in this field, resulting in 21 candidates. For one of these, AT2019osy, we performed multiwavelength follow-up and ultimately ruled out the association with S190814bv. All other candidates are likely unrelated variables, but we cannot conclusively rule them out. We discuss our results in the context of model predictions for radio emission from NSBH mergers and place constrains on the circum-merger density and inclination angle of the merger. This survey is simultaneously the first large-scale radio follow-up of an NSBH merger, and the most sensitive widefield radio transients search to-date.

Black hole (networking)

Pathfinder

10.3847/2041-8213/ab59db

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A Strong Jet Signature in the Late-time Light Curve of GW170817

The Astrophysical Journal Letters (2018)

K. P. Mooley D. A. Frail Dougal Dobie E. Lenc A. Corsi

Abstract We present new 0.6–10 GHz observations of the binary neutron star merger GW170817 covering the period up to 300 days post-merger, taken with the upgraded Karl G. Jansky Very Large Array, the Australia Telescope Compact Array, the Giant Metrewave Radio Telescope and the MeerKAT telescope. We use these data to precisely characterize the decay phase of the late-time radio light curve. We find that the temporal decay is consistent with a power-law slope of t −2.2 , and that the transition between the power-law rise and decay is relatively sharp. Such a slope cannot be produced by a quasi-isotropic (cocoon-dominated) outflow, but is instead the classic signature of a relativistic jet. This provides strong observational evidence that GW170817 produced a successful jet, and directly demonstrates the link between binary neutron star mergers and short-hard gamma-ray bursts. Using simple analytical arguments, we derive constraints on the geometry and the jet opening angle of GW170817. These results are consistent with those from our companion very long baseline interferometry paper, reporting superluminal motion in GW170817.

Superluminal motion

Jansky

Very-long-baseline interferometry

10.3847/2041-8213/aaeda7

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Radio transients and variables in the tenth Deeper, Wider, Faster observing run

Monthly Notices of the Royal Astronomical Society (2022)

Dougal Dobie Joshua Pritchard Yuanming Wang L. W. Graham James Freeburn

ABSTRACT The Deeper, Wider, Faster (DWF) program coordinates observations with telescopes across the electromagnetic spectrum, searching for transients on time-scales of milliseconds to days. The tenth DWF observing run was carried out in near real-time during September 2021, and consisted of six consecutive days of observations of the NGC 6744 galaxy group and a field containing the repeating fast radio burst FRB 190711 with the Australian Square Kilometre Array Pathfinder, the Dark Energy Camera, the Hard X-ray Modulation Telescope, and the Parkes 64-m ‘Murriyang’ radio telescope. In this work, we present the results of an image-domain search for transient, variable, and circularly polarized sources carried out with ASKAP, using data from the observing run along with test observations prior to the run and follow-up observations carried out during and after the run. We identified eight variable radio sources, consisting of one pulsar, six stellar systems (five of which exhibit circularly polarized emission), and one previously uncatalogued source. Of particular interest is the detection of pulses from the ultra-cool dwarf SCR J1845–6357 with a period of 14.2 ± 0.3 h in good agreement with the known optical rotation period, making this the slowest rotating radio-loud ultra-cool dwarf discovered.

Galactic astronomy

Variable star

10.1093/mnras/stac3731

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The Panchromatic Afterglow of GW170817: The full uniform dataset, modeling, comparison with previous results and implications

arXiv (Cornell University) (2020)

Sphesihle Makhathini K. P. Mooley Murray Brightman Kenta Hotokezaka A. J. Nayana

We present the full panchromatic afterglow light curve data of GW170817, including new radio data as well as archival optical and X-ray data, between 0.5 and 940 days post-merger. By compiling all archival data, and reprocessing a subset of it, we have evaluated the impact of differences in data processing or flux determination methods used by different groups, and attempted to mitigate these differences to provide a more uniform dataset. Simple power-law fits to the uniform afterglow light curve indicate a $t^{0.86\pm0.04}$ rise, a $t^{-1.92\pm0.12}$ decline, and a peak occurring at $155\pm4$ days. The afterglow is optically thin throughout its evolution, consistent with a single spectral index ($-0.584\pm0.002$) across all epochs. This gives a precise and updated estimate of the electron power-law index, $p=2.168\pm0.004$. By studying the diffuse X-ray emission from the host galaxy, we place a conservative upper limit on the hot ionized ISM density, $<$0.01 cm$^{-3}$, consistent with previous afterglow studies. Using the late-time afterglow data we rule out any long-lived neutron star remnant having magnetic field strength between 10$^{10.4}$ G and 10$^{16}$ G. Our fits to the afterglow data using an analytical model that includes VLBI proper motion from Mooley et al. (2018), and a structured jet model that ignores the proper motion, indicates that the proper motion measurement needs to be considered while seeking an accurate estimate of the viewing angle.

Panchromatic film

Very-long-baseline interferometry

Proper motion

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Citations (18)

LIGO/Virgo G298048: Correction to ATCA 8.5 GHz observations

GRB Coordinates Network (2017)

C. Lynch Thomas W. Murphy David E. Kaplan K. W. Bannister Dougal Dobie

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LIGO/Virgo G298048: ATCA observations of candidate host galaxies

GRB Coordinates Network (2017)

K. W. Bannister C. Lynch David E. Kaplan Tara Murphy Dougal Dobie

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Characterizing Pulsars Detected in the Rapid ASKAP Continuum Survey

arXiv (Cornell University) (2023)

Akash Anumarlapudi Anna Ehlke Megan L. Jones D. L. Kaplan Dougal Dobie

We present the detection of 661 known pulsars observed with the Australian SKA Pathfinder (ASKAP) telescope at 888 MHz as a part of the Rapid ASKAP Continuum Survey (RACS). Detections were made through astrometric coincidence and we estimate the false alarm rate of our sample to be ~0.5%. Using archival data at 400 and 1400 MHz, we estimate the power law spectral indices for the pulsars in our sample and find that the mean spectral index is -1.78 +/- 0.6. However, we also find that a single power law is inadequate to model all the observed spectra. With the addition of the flux densities between 150 MHz and 3 GHz from various imaging surveys, we find that up to 40% of our sample shows deviations from a simple power law model. Using Stokes V measurements from the RACS data, we measured the circular polarization fraction for 9% of our sample and find that the mean polarization fraction is ~10% (consistent between detections and upper limits). Using the dispersion measure (DM) derived distance we estimate the pseudo luminosity of the pulsars and do not find any strong evidence for a correlation with the pulsars' intrinsic properties.

Spectral index

10.48550/arxiv.2308.00100

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LIGO/Virgo S190814bv: Additional candidates identified in DECam images by the DECam-GROWTH team

GRB Coordinates Network (2019)

D. A. Goldstein Igor Andreoni M. Hankins J. Sollerman Shreya Anand

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Radio afterglows from tidal disruption events: An unbiased sample from ASKAP RACS

arXiv (Cornell University) (2024)

Akash Anumarlapudi Dougal Dobie D. L. Kaplan Tara Murphy A. Horesh

Late-time ($\sim$ year) radio follow-up of optically-discovered tidal disruption events (TDEs) is increasingly resulting in detections at radio wavelengths, and there is growing evidence for this late-time radio activity to be common to the broad class of sub-relativistic TDEs. Detailed studies of some of these TDEs at radio wavelengths are also challenging the existing models for radio emission. Using all-sky multi-epoch data from the Australian Square Kilometre Array Pathfinder (ASKAP), taken as a part of the Rapid ASKAP Continuum Survey (RACS), we searched for radio counterparts to a sample of optically-discovered TDEs. We detected late-time emission at RACS frequencies (742-1032\,MHz) in five TDEs, reporting the independent discovery of radio emission from TDE AT2019ahk and extending the time baseline out to almost 3000\,days for some events. Overall, we find that at least $22^{+15}_{-11}$\% of the population of optically-discovered TDEs has detectable radio emission in the RACS survey, while also noting that the true fraction can be higher given the limited cadence (2 epochs separated by $\sim 3\,$ years) of the survey. Finally, we project that the ongoing higher-cadence ($\sim 2$\,months) ASKAP Variable and Slow Transients (VAST) survey can detect $\sim 20$ TDEs in its operational span (4\,yrs), given the current rate from optical surveys.

Sample (material)

10.48550/arxiv.2407.12097

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