LIGO/Virgo S190814bv: No radio counterpart detected in ASKAP observations
Abstract
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/
- Publication:
-
GRB Coordinates Network
- Pub Date:
- August 2019
- Bibcode:
- 2019GCN.25445....1D