GCN Circular 42663
P.J. Groot (Radboud/UCT/SAAO) , H. Tranin (Barcelona), J. van Roestel (ISTA), P.M. Vreeswijk (Radboud), D. Pieterse (Radboud), G. Leloudas (DTU Space), N. Blagorodnova (Barcelona), S. Bloemen (Radboud), G. Ramsay (Armagh), S. Scaringi (Durham) report on behalf of the BlackGEM and MeerLICHT consortia:
"The BlackGEM and MeerLICHT telescopes (Groot et al., 2024) reacted to the LVK-announced gravitational wave event S251112cm (LVK2025, GCN Circ. 42650). Both telescope systems covered about 50% of the 90% error box, primarily the part located in the Southern Hemisphere. A detailed overview of observations will be given in a subsequent report. Here we report the detection of AT2025adgp (BGEM J014746.20-514925.5), and AT2025adgq (MLT J002931.8-393051.6) as two newly detected transients in the BlackGEM/MeerLICHT footprint, which, on average, had a limiting magnitude for new transients of q~19.8.
AT2025adgp is located at RA, Dec (ICRS) = 01:47:46.202 -51:49:25.52 (26.942508d, -51.823756d) with an uncertainty of 0.1" in each coordinate. It was detected on 2025-11-13 03:09:48 and 03:25:29 UT in the BlackGEM q-band (440-720 nm) filter using the BG-2 telescope, at, respectively, q=19.31+/-0.12 and q=19.29+/-0.12. The first detection was 11h50m after the LVK Trigger time. The transient is located in the southern outskirts of a face-on spiral galaxy WISExSCOS J014746.23-514922.5, listed in the Regalade catalog (Tranin et al., 2025) at a luminosity distance of D_L =246 Mpc with a large standard deviation, and in the GLADE+ (Dalya et al., 2020) catalog at D_L = 250 +/- 45 Mpc. If the galaxy is the host of AT2025adgp this would put its distance at the upper edge of consistency with the distance to S251112cm as announced by the LVK collaboration at D_S251112cm = 96 +/- 29 Mpc.
AT2025adgq is located at RA,Dec (ICRS) = 00:29:31.8, -39:30:51.6 (7.38245842d, -39.5143190d) with an uncertainty of 0.1” in each coordinate. It was detected on 2025-11-13 00:03:38 and 00:04:43 UT in the BlackGEM q-band (440-720 nm) filter using the MeerLICHT telescope at, q=19.28+/-0.10 in each exposure. The first detection was 08h44m after the LVK trigger. The BlackGEM array also detected AT2025adgq on 2025-11-13 01:05:23 UT and 01:22:00 UT using the BG-2 telescope at q=19.28 +/- 0.10 and q=19.41 +/- 0.1, respectively. The transient is located in the north-eastern elongation of an oblated galaxy, WISExSCOS J002932.49-393059.7, listed in the Regalade catalog at a luminosity distance of D_L = 279 +/- 130 Mpc, and in the GLADE+ catalog at D_L = 300 +/- 68 Mpc. If the galaxy is the host of AT2025adqp this would put its distance at the upper edge of consistency with the distance to S251112cm as announced by the LVK collaboration.
We encourage spectroscopic classification of AT2025adgp and AT2025adgq to confirm their nature and distance, and therefore the possibility of them being a counterpart to S251112cm."
References: Groot et al., 2024, PASP 136, 5003, Tranin et al., 2025, arXiv250813267T, Dalya et al., 2020, VizieR On-line Data Catalog: VII/275; LVK2025, 2025, GCN 42650