TITLE: GCN CIRCULAR NUMBER: 39286 SUBJECT: LIGO/Virgo/KAGRA S250206dm: continued in SOAR galaxy targeted observations and identification of one possible transient DATE: 25/02/11 15:01:05 GMT FROM: James Freeburn at Swinburne University of Technology jamesfreeburn54@gmail.com
James Freeburn (Swinburne/OzGrav), Sarah Teague (UNC), Jonathan Carney (UNC), Igor Andreoni (UNC), Charles Kilpatrick (Northwestern), Olga Volchansky (UMD), Andre Santos (CBPF), Clecio De Bom (CBPF):
We continued (Freeburn et al., GCN 39196) follow up observations of the gravitational wave trigger S250206dm (GCN 39175, GCN 39178, GCN 39184, GCN 39231) using the Goodman High Throughput Spectrograph mounted on the SOAR 4.1-meter telescope in imaging mode via Target of Opportunity observations (PI Andreoni). We observed 30 galaxies in the highest probability region (Cook at al. GCN 39174, GCN 39177, GCN 39185, GCN 39235) using the list produced by crossmatching the sky localization with the NED Local Volume Sample (NED-LVS; Cook et al. 2023). Specifically, we considered the galaxy list obtained using the LVK S250206dm-7-Update sky localization (Cook at al. GCN 39235), focusing on the Southern high probability area.
Observations were acquired from 2025-02-09 06:48 UT until 09:18 UT. Each galaxy was observed with 3 x 60s exposures in i-band which resulted in a typical depth of ~22 AB magnitude.
We used the SOAR/Goodman observations from 2025-02-07 (Freeburn et al. GCN 39196) as science images and the observations from 2025-02-09 as templates. From a preliminary analysis of the resultant difference images, we find one low significance candidate, AT2025ber, at 16:31:50.40 -69:31:44.29, in the 51% localisation contour of the S250206dm updated skymap. It is in the vicinity of the NED-LVS galaxy WISEA J163202.83-693109.0, which is a galaxy with a spectroscopic redshift of z=0.07743 and a luminosity distance of 354.7 Mpc. The separation distance between WISEA J163202.83-693109.0 and AT2025ber is ~100kpc. Given this large separation distance, it is unlikely that WISEA J163202.83-693109.0 is the host galaxy to AT2025ber, but such a large separation would not be unprecedented for a compact binary merger (see, e.g., Fong et al. 2013). The photometry is provided below in AB magnitudes:
2025-02-07 i = 22.0 +/- 0.2 g > 22.4
2025-02-09 i > 22.2
From MPChecker, we do not find any known asteroid associated with AT2025ber. However, given the brightness of this event, and the fact that it was found in a single image, we caution the possibility that this is an uncatalogued asteroid. There is no coincident source in archival DELVE data (Drlica-Wagner et al., 2021) which places upper limits in gri > 23.5 AB mag.
A list of the observed galaxies which are still within the 90% probability volume is presented in the table below. The completed pointings were uploaded to TreasureMap: https://treasuremap.space/alerts?graceids=S250206dm
object_name coordinates WISEA J161708.84-674024.7 16:17:08.87 -67:40:22.49 WISEA J162759.57-693615.7 16:27:59.57 -69:36:15.71 WISEA J154439.56-665529.0 15:44:39.56 -66:55:29.08 WISEA J155633.83-693531.5 15:56:33.83 -69:35:31.55 WISEA J160843.41-685023.4 16:08:43.41 -68:50:23.44 WISEA J160915.94-690504.9 16:09:15.95 -69:05:04.94 WISEA J161332.77-674621.1 16:13:32.78 -67:46:21.13 WISEA J165614.58-695645.9 16:56:14.58 -69:56:46.00 WISEA J163330.53-670950.7 16:33:30.54 -67:09:50.72 WISEA J154538.24-703944.1 15:45:38.25 -70:39:44.12 WISEA J153057.77-694546.5 15:30:57.77 -69:45:46.58 WISEA J160838.27-700230.8 16:08:38.27 -70:02:30.85 WISEA J161213.79-710729.1 16:12:13.79 -71:07:29.14 WISEA J165744.21-680430.9 16:57:44.21 -68:04:30.93 WISEA J163202.83-693109.0 16:32:02.84 -69:31:09.01 WISEA J164922.44-690054.7 16:49:22.44 -69:00:54.76 WISEA J161735.32-701416.0 16:17:35.32 -70:14:16.00 WISEA J163253.56-702946.2 16:32:53.57 -70:29:46.22 ESO 069- G 003 16:24:32.07 -68:49:12.91 WISEA J161946.23-690837.2 16:19:46.23 -69:08:37.26 WISEA J155653.84-695749.1 15:56:53.88 -69:57:49.18 WISEA J165438.30-670413.8 16:54:38.30 -67:04:13.82 WISEA J163224.97-700239.7 16:32:24.97 -70:02:39.78 WISEA J155231.27-695346.6 15:52:31.31 -69:53:46.61 WISEA J155145.65-695137.1 15:51:45.63 -69:51:36.90 WISEA J154932.61-695540.7 15:49:32.96 -69:55:41.02 WISEA J160323.17-681358.2 16:03:23.27 -68:14:00.31 WISEA J160100.07-690900.0 16:01:00.10 -69:09:00.00 WISEA J161133.67-692644.0 16:11:33.73 -69:26:43.58 WISEA J161459.65-691110.1 16:15:05.66 -69:11:09.89
We thank the NOIRLab and SOAR staff for their excellent support.
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