GCN Circular 25445
Subject
LIGO/Virgo S190814bv: No radio counterpart detected in ASKAP observations
Date
2019-08-22T07:57:20Z (5 years ago)
From
Dougal Dobie at VAST <ddobie94@gmail.com>
Dougal Dobie (University of Sydney/CSIRO), Adam Stewart (University of Sydney),
Ziteng Wang (University of Sydney), Tara Murphy (University of
Sydney),Emil Lenc (CSIRO),
David Kaplan (UWM), Aidan Hotan (CSIRO), Kunal Mooley (NRAO, Caltech),
Gregg Hallinan (Caltech),
David McConnell (CSIRO), Julie Banfield (CSIRO), Wasim Raja (CSIRO),
Matthew Whiting (CSIRO),
Vanessa Moss (CSIRO), Igor Andreoni (Caltech) and the OzGrav, JAGWAR
and GROWTH collaborations.
We report observations of the localisation region of S190814bv (LVC,
GCN 25324) with the
Australian Square Kilometre Array Pathfinder (ASKAP) on 2019-08-16 at
a central frequency
of 943 MHz with a bandwidth of 288 MHz.
We have observed a single 30 sq. deg. field centered on
RA = 00:50:37.5
Dec = -25:16:57.4
which covers approximately 85% of the sky localisation from the
LALInference skymap (GCN 25333),
with a median rms of 34 uJy.
We have searched for radio emission within 5 arcseconds of the
location of the 124 optical transients
reported on the Transient Name Server by the DECam-GROWTH and DESGW
teams between 2019-08-16 and 2019-08-22
as at 2019-08-22 03:00 UTC. We report coincident compact radio
emission at the location of 14 of them:
| Name | RA | Dec | Int. Flux (uJy) | err. (uJy) | Notes |
| AT 2019nqa | 00:52:39.1 | -25:00:15 | 258 | 30 | |
| AT 2019nqy | 00:56:23.2 | -24:41:11 | 393 | 29 | |
| AT 2019nqz | 00:46:46.5 | -24:20:12 | 870 | 30 | (a) |
| AT 2019nsr | 00:57:27.6 | -26:16:44 | 290 | 36 | (c) |
| AT 2019nto | 00:42:03.5 | -24:48:19 | 342 | 28 | (c) |
| AT 2019nuk | 00:54:57.9 | -26:08:03 | 233 | 28 | (b) |
| AT 2019nul | 00:55:16.4 | -26:56:35 | 204 | 28 | (b) |
| AT 2019nun | 00:56:48.7 | -24:54:31 | 377 | 29 | (b,c) |
| AT 2019nuo | 00:56:03.9 | -23:18:15 | 388 | 36 | (c) |
| AT 2019nup | 00:55:04.3 | -26:46:12 | 446 | 33 | (c) |
| AT 2019nzj | 00:52:05.3 | -26:11:03 | 759 | 29 | |
| AT 2019nzn | 00:55:19.9 | -24:09:29 | 233 | 32 | (c) |
| AT 2019oay | 00:45:25.2 | -25:53:43 | 348 | 31 | |
| AT 2019ocs | 01:00:11.4 | -25:53:22 | 352 | 29 | |
(a) reported in GCN25391
(b) reported in GCN25393
(c) source possibly extended
We have also performed a preliminary search for transients using TraP
(Swinbank et al. 2015) comparing this
observation to the Rapid ASKAP Continuum Survey (RACS, [1]) at a
detection threshold of 0.95 mJy, corresponding
to 5 times the lowest rms of the RACS image. We find one candidate
transient located at
RA = 00:54:34.6 +/- 0.02 arcsec
Dec = -28:02:35.3 +/- 0.01 arcsec
which we note is outside the 95% confidence region of S190814bv. We
measure a flux density of 3.4 mJy in this
observation and a local rms noise of 0.25 mJy in the 888 MHz RACS
image observed on 2019-04-26. We measured an
integrated flux density of 0.74 mJy in the RACS image using TraP. We
also note that there is a radio source
coincident with this location in the image from the Very Large Array
Sky Survey (VLASS) observed on 2019-06-29
with a flux density of ~1.6 mJy at 3 GHz.
We conducted follow-up of this source with the Australia Telescope
Compact Array (ATCA) on 2019-08-21 with two
2048 MHz bands centered on 5.5 and 9 GHz. We measure preliminary flux
densities of 2.88 +/- 0.03 mJy and
2.93 +/- 0.02 mJy at 5.5 and 9 GHz, with respective in-band spectral
indices of +0.17 and -0.37.
Combining the near-contemporaneous ATCA and ASKAP measurements we find
a flat spectral index. Based on these
observations this candidate is likely to be an unrelated AGN.
The ASKAP observation is publicly available on the CSIRO ASKAP Science
Data Archive [2] under Scheduling Block ID 9602.
Further analysis of this ASKAP observation is ongoing and further
epochs are planned.
Thank you to CSIRO staff for supporting these observations.
[1] https://www.atnf.csiro.au/content/racs
[2] https://casda.csiro.au/