TITLE: GCN CIRCULAR NUMBER: 25445 SUBJECT: LIGO/Virgo S190814bv: No radio counterpart detected in ASKAP observations DATE: 19/08/22 07:57:20 GMT FROM: Dougal Dobie at VAST 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/