LIGO/Virgo/KAGRA S251112cm
GCN Circular 42867
Mankeun Jeong, Myungshin Im, Seo-Won Chang, Hyeonho Choi (SNU/SNU ARC), Gregory S.-H. Paek (IfA), and Chung-Uk Lee (KASI), on behalf of the GECKO team
We observed the S251112cm sky localization region (Updated; GCN 42690) following the LIGO/Virgo/KAGRA trigger. Optical imaging was obtained with the three 1.6-m Korea Microlensing Telescope Network (KMTNet) telescopes at CTIO, SAAO, and SSO, with most of the data taken from SSO.
We surveyed the southern portion (decl. < -10 deg) of the S251112cm 90% localization region, covering ~1,012 deg^2 from 2025-11-13 to 2025-11-27. During the first three nights, we obtained R and I imaging with 480 sec total exposure per field (four dithered 120 sec exposures) over ~180 deg^2. For the remainder of the run, observations were conducted in R-band only with the same 480 sec per-field exposure.
A fraction of the surveyed area overlaps with regions having KMTNet Synoptic Survey of the Southern Sky (KS4) reference images. Difference image analysis has been completed for ~60 deg^2, with additional processing ongoing.
Below we list transient candidates re-identified from TNS and new GECKO sources detected in our imaging. Redshifts are adopted from the GLADE+ host-galaxy associations.
| Name | RA (deg) | Dec (deg) | R (AB mag) | I (AB mag) | Date-Obs (UTC) | Redshift |
|---|---|---|---|---|---|---|
| AT2025aebs | 354.16948 | -33.01666 | 20.42 ± 0.05 | 20.66 ± 0.07 | 2025-11-16T12:24:50 | 0.1642 |
| AT2025adbw | 3.31215 | -36.40843 | 19.07 ± 0.02 | — | 2025-11-14T14:23:37 | — |
| AT2025abnc | 7.50565 | -34.96515 | 19.95 ± 0.05 | 20.54 ± 0.08 | 2025-11-14T12:40:10 | 0.1067 |
| GECKO25dryb | 1.69517 | -33.38614 | 18.95 ± 0.01 | 19.05 ± 0.05 | 2025-11-14T13:39:42 | 0.2094 |
| GECKO25drxk | 1.53192 | -35.03043 | 18.89 ± 0.01 | 18.86 ± 0.03 | 2025-11-14T13:39:42 | 0.2408 |
| GECKO25dulp | 358.59508 | -35.91373 | 19.58 ± 0.06 | 18.65 ± 0.03 | 2025-11-16T13:40:59 | 0.0859 |
| GECKO25dukb | 356.10091 | -34.07094 | 18.37 ± 0.01 | 18.13 ± 0.01 | 2025-11-16T12:24:50 | 0.1269 |
All newly identified GECKO candidates lie close to the center of the host galaxy, whose redshifts exceed the estimated distance of S251112cm, indicating they are unrelated to the GW event's physical origin.
Further difference imaging and transient vetting across the remaining fields are underway.
The GECKO network (Im et al. 2023; Paek et al. 2024) operates 0.5–1 m class telescopes worldwide for EM follow-up of gravitational-wave events. KMTNet is operated by the Korea Astronomy and Space Science Institute. We thank the KMTNet staff for their support during these observations.
GCN Circular 42825
J. H. Gillanders (Oxford), A. Aryan, T.-W. Chen, Y.-H. Lee, C.-S. Lin (all NCU), A. K. H. Kong (NTHU), S. J. Smartt (Oxford), Y. J. Yang (NYUAD), A. Sankar.K, Y.-C. Pan, C.-C. Ngeow, M.-H. Lee, C.-H. Lai, W.-J. Hou, H.-C. Lin, H.-Y. Hsiao, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, L. L. Fan, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report:
Here we report follow-up observations of the candidate optical counterpart AT 2025adht (first reported by Franz et al., GCN 42675; see also Anand et al., GCN 42677; Burkhonov et al., GCN 42798) to the LIGO-Virgo-KAGRA (LVK) gravitational-wave event S251112cm (LVK Collaboration, GCN 42650).
We observed AT 2025adht utilizing the 1m LOT at Lulin Observatory in Taiwan, as part of the Kinder collaboration (Chen & Yang et al. 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). The first LOT epoch of observations began at 20:31 UTC on November 21, 2025 (MJD 61000.855), 9.225 days after the GW trigger. The second LOT epoch began at 20:16 UTC, or MJD 61001.845, 10.207 days after the GW trigger.
We utilized the astroalign (Beroiz et al. 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al. 2022, ApJ, 935, 167) packages to align and stack the individual frames. We utilized the Python-based package AutoPhOT (Brennan & Fraser 2022, A&A, 667, A62) to perform template subtraction with the DESI Legacy Survey (Dey et al. 2019, AJ 157, 168) DR10 images using the 'hotpants' (Becker 2015, ascl.soft. ascl:1504.004) algorithm.
Moreover, we further utilized AutoPhOT to perform PSF photometry. The details of the observations and the measured magnitudes (in the AB system) are as follows:
Telescope | Filter | MJD (start) | t - t0 (d) | Exposure (s) | Magnitude | avg. Seeing | med. Airmass
LOT | r | 61000.855 | 9.225 | 300 * 6 | 21.83 +/- 0.06 | 1".2 | 1.41
LOT | r | 61001.845 | 10.207 | 300 * 6 | 21.86 +/- 0.08 | 1".2 | 1.46
Burkhonov et al. (GCN 42698) report a (PS1-equivalent) r-band magnitude of 21.64 +/- 0.1 on MJD 60994.009 (2.37 days post-GW trigger). Our observations indicate that AT 2025adht has faded only slightly in the ~week since detection. The slow evolution indicates that AT 2025adht is not some rapidly declining kilonova-like transient; we instead suspect that AT 2025adht is a background supernova near peak, hence the slow evolution. This interpretation is supported by the Legacy Survey's host galaxy phot-z estimate (0.139 +/- 0.033; see also Anand et al., GCN 42677).
The presented magnitudes are calibrated using field stars from the ATLAS-RefCat2 catalog from MAST (Tonry et al. 2018, ApJ, 867, 105) and are not corrected for the expected Galactic foreground extinction of A_r = 0.06 mag in the direction of the transient (Schlafly & Finkbeiner 2011). The methodology and details on the capabilities of Lulin observatory telescopes can be found in Aryan et al. 2025, ApJS, 281, 20. doi:10.3847/1538-4365/adfc69.
GCN Circular 42796
Hemanth Bommireddy (U de Chile), Regis Cartier (UA), Felipe Olivares (U Hawaii), reporting on behalf of the Dark Energy Survey Gravitational Wave (DESGW) spectroscopy team:
We report spectroscopic observations of the transients AT2025adgp, AT2025adhf, and AT2025adhs obtained with the SOAR telescope on 2025-11-14 at 04:10:05 UTC (PI: Bommireddy). For each source, we obtained an exposure of approximately 900s. The spectra were preliminarily reduced and classified using the NGSF spectral classification software (Goldwasser et al. 2022). Based on the reported redshifts (GCN 42675), the top 3 template fits for each event are listed below.
| event | SN type/event/instrument (χ²/dof) |
|---|---|
| AT2025adgp | II/2013fs/KAST (~0.83), Ic-BL/1998bw/DFOSC (~0.82), IIn/2010jl/KAST (~0.88) |
| AT2025adhf | Ic-BL/1998bw/DFOSC (~1.96), Ic-BL/1998bw/EFOSC2-3.6 (~1.99), Ic-BL/1998bw/DFOSC (~2.06) |
| AT2025adhs | SLSN-I/PTF10aagc/LRIS (~1.57), Ia-pec/2000cx/KAST (~1.61), SLSN-I/PTF12dam/DBSP (~1.62) |
We thank the SOAR staff for their support during these observations.
GCN Circular 42777
Y. N. Ma, L. P. Xin, Z. H. Yao, Y. L. Qiu, C. Wu, H. L. Li, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team.
SVOM/VT performed the Target of Opportunity observations of 3 candidates of S251112cm reported by LIGO/Virgo/KAGRA (GCN 42650, GCN 42690). SVOM/VT began observing the field at 2025-11-17, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
We observed AT2025adhf (GCN 42675, GCN 42724), AT2025adkl (GCN 42691), and AT2025addc (GCN 42658), which were reported by the Vera C. Rubin Observatory (GCN 42707). We found that AT2025adhf is located within a galaxy, while AT2025adkl is situated at a galaxy's edge. Here we provide the total magnitudes of the supernovae and the galaxies (using the galactic nuclei as the photometric center), since we do not have the templates for this sources. AT2025addc is an isolated source, and we also provide its magnitude. The magnitudes are:
Name |Observation Date(UTC) |VT_B(AB_mag) |VT_R(AB_mag)
----------------------|----------------------|-------------|-------------
AT2025adhf(+galaxy) |2025-11-17 |17.19+-0.01 |16.41+-0.01
AT2025adkl(+galaxy) |2025-11-18 |20.14+-0.05 |19.50+-0.04
AT2025addc |2025-11-17 |20.45+-0.04 |20.75+-0.07
Our photometry was not corrected for Galactic extinction.
Further analysis of these candidates is ongoing.
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.
GCN Circular 42746
M. Kerr, C.C. Cheung, R. Woolf, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report:
The compact binary merger candidate S251112cm (event time, T0 = 2025-11-12T15:19:22.360 UTC) was identified in LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) data (GCN 42690).
The Glowbug gamma-ray instrument [1,2,3] observed much of the sky to which a high probability for the candidate origin was assigned. Glowbug has an all-sky field-of-view limited only by earth occultation and large-scale structures on the International Space Station (ISS). At T0, the Glowbug boresight was pointed towards R.A., Dec. = 92, 22 deg. We examined three high-probability regions in the contours with positions R.A., Dec. = 346, -13 deg; 173, 43 deg; and 149, 6.5 deg, which were at zenith angles of 110 deg., 68 deg., and 57 deg., respectively, all nominally above the limb of the earth. Positions at lower zenith angles, however, are more likely to be obstructed by ISS structure.
Using 50-2000 keV data and two representative (normal and hard spectrum) GRB templates from [4], we searched for transient gamma-ray signals using maximum likelihood methods and found no plausible counterpart up to 30s before or after T0. We determined 3-sigma upper limits on the flux for a GRB at the three trial positions by selecting data centered on T0 and integrating the posterior probability to determine the flux beyond which the tail probability is 0.27%. For various timescales and the two GRB spectral templates, the range of limits (over the three positions) in units of 1e-7 erg/cm2/s are:
Timescale Normal Hard
------------------------------------
0.128 s: 1.4-2.8 3.0-6.0
1.024 s: 0.8-1.0 1.5-2.0
8.192 s: 0.2-0.4 0.4-1.0
These results do not account for scattering or occultation by structures on the ISS. We do not report results for an assumed soft spectrum due to a likely increase in the low-energy threshold of Glowbug due to accumulated radiation exposure.
The Glowbug sky coverage is complementary to that obtained by Fermi/GBM (GCN 42655).
Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12.
[1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959
[2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O
[3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108
[4] Goldstein, A. et al. 2020, ApJ 895, 40, arXiv:1909.03006
Distribution Statement A: Approved for public release. Distribution is unlimited.
GCN Circular 42725
Kenta Taguchi, Miho Kawabata (Kyoto U.); Ryosuke Itoh (Ibara City); Hiroshi Akitaya, Tomoki Morokuma (ARC/Chiba Tech); Jun Takahashi, Satoshi Honda, Miyako Tozuka, Shigeru Takahashi (Univ. of Hyogo/NHAO); Koji Kawabata, Tatsuya Nakaoka (Hiroshima U.); Haruna Hagio, Ryotaro Kato, Atsuya Ochi, Mahito Sasada, Ichiro Takahashi (Science Tokyo); Nozomu Tominaga, Yousuke Utsumi, Michitoshi Yoshida, Haibin Zhang, Masafumi Niwano, Mitsuru Kokubo, Yuhei Iwata (NAOJ); Masaomi Tanaka (Tohoku University); Yuu Niino, Taiga Sasaoka (U. of Tokyo); Yumiko Oasa, Takahiro Kanai (Saitama Univ.); Yuichiro Sekiguchi (Toho University) on behalf of the J-GEM collaboration
We report imaging follow-up observations for the gravitational-wave event S251112cm (GCN 42650).
Our observations started at 2025-11-12 19:09:29 UT (MJD=60991.80), approximately 3.8 hours after the event, and ended at 2025-11-17 10:18:47 UT (MJD=60996.43).
We conducted galaxy-targeted observations of 135 galaxies (see the table below), selected from the GLADE catalog (v2.4; Dalya et al. 2018) within the probability skymap of S251112cm, using the telescopes and instruments listed below.
After screening out known minor planets, we did not find any apparent transient candidates in these galaxies down to the 5-sigma limiting magnitudes in the AB magnitude system summarized below.
galid ra dec dist g r R i I z J H Ks NoFilt obsid
--------------- -------- -------- ------ ---- ---- ---- ---- ---- ---- ---- ---- ---- ------ -------
GL000835-335128 2.1441 -33.8578 97.4 -- -- 17.2 -- -- -- -- -- -- -- 1
GL094621+030417 146.5879 3.0713 86.9 19.6 18.6 -- 18.8 -- -- -- -- -- 18.3 2,3
GL095807+102135 149.5288 10.3598 77.8 20.4 19.9 19.8 19.8 18.0 -- -- 15.8 -- -- 4,5,2
GL102235+195314 155.6440 19.8871 82.7 19.9 19.6 18.7 19.6 18.0 -- -- -- -- 19.0 5,2,3
GL094620+030244 146.5848 3.0455 87.3 19.6 18.6 -- 18.8 -- -- -- -- -- 18.3 2,3
GL094604+042412 146.5148 4.4033 71.9 18.0 17.1 -- 17.2 -- -- -- -- -- 18.5 2,3
GL093427-023015 143.6119 -2.5041 78.1 19.6 18.6 20.1 18.9 -- -- -- 16.8 -- 14.9 2,3,4
GL100140+104523 150.4186 10.7564 78.3 19.9 19.5 18.6 19.5 17.9 -- -- -- -- 18.6 5,2,3
GL103939+251921 159.9126 25.3226 75.2 19.8 -- 19.9 19.1 -- -- -- 15.8 -- 18.9 2,3,4
GL092022-075250 140.0914 -7.8807 49.6 19.2 18.4 19.6 18.6 -- -- -- 17.2 -- 18.5 2,4,3
GL224424-000943 341.1015 -0.1620 70.1 -- -- 18.2 -- -- -- -- 18.8 -- 19.4 1,3,6
GL094909+022851 147.2866 2.4808 88.5 20.4 19.6 15.3 19.3 15.1 -- -- -- -- 14.5 5,2,3
GL094559+030843 146.4950 3.1453 85.8 19.7 19.0 -- 18.8 -- -- -- -- -- 18.2 2,3
GL102905+221246 157.2692 22.2128 92.9 20.0 19.4 -- 19.2 -- -- -- -- -- 19.1 2,3
GL230311-085921 345.7959 -8.9890 104.2 20.4 19.6 -- 19.8 -- -- -- -- 17.6 19.2 2,3,6
GL094036+033437 145.1516 3.5769 73.2 18.3 17.3 -- 17.5 -- 16.5 -- -- -- -- 7,2
GL234745-280828 356.9380 -28.1410 124.7 18.3 17.6 -- 23.8 -- -- -- -- -- -- 2
GL234045-244137 355.1890 -24.6937 98.5 -- 18.5 -- 19.2 -- -- -- -- -- 18.9 3,2
GL230344-071330 345.9325 -7.2250 74.5 20.2 19.7 18.6 19.9 18.2 18.2 -- -- -- 19.0 2,7,3,5
GL103958+240528 159.9915 24.0912 91.6 19.7 18.8 -- 18.8 -- -- -- -- -- -- 2
GL093941-001406 144.9204 -0.2351 72.2 17.1 16.5 -- 16.4 -- -- -- -- -- 17.8 2,3
GL103130+245210 157.8750 24.8693 90.7 19.6 18.6 -- 18.4 -- -- -- -- -- 18.7 2,3
GL110800+365220 166.9981 36.8722 116.9 20.2 19.4 -- 19.4 -- -- -- -- -- 19.0 2,3
GL234729-280634 356.8690 -28.1093 120.3 18.3 17.6 -- 23.8 -- -- -- -- -- -- 2
GL235137-282154 357.9030 -28.3651 121.0 18.4 18.0 -- -- -- -- -- -- -- 18.6 3,2
GL101229+122237 153.1220 12.3771 79.2 19.7 19.3 -- 19.2 -- -- -- -- -- 18.7 2,3
GL093411+001431 143.5443 0.2420 70.9 20.2 19.7 18.6 19.7 17.9 -- -- 17.8 -- 17.7 5,2,3,4
GL225651-085803 344.2120 -8.9674 72.7 -- -- -- -- -- -- 17.9 17.9 -- 19.0 3,6
GL225542-052943 343.9238 -5.4953 43.8 19.2 -- -- 18.2 -- -- -- -- -- 19.4 2,3
GL104801+281447 162.0045 28.2464 92.0 21.6 21.2 -- 21.2 -- -- -- -- -- 21.1 2,3
GL092514-064300 141.3074 -6.7166 88.7 20.0 19.4 -- 19.4 -- -- -- -- -- 18.9 2,3
GL104437+261054 161.1539 26.1816 90.8 -- -- -- -- -- -- -- -- -- 18.9 3
GL232431-190333 351.1310 -19.0591 110.5 19.9 18.8 -- 18.9 -- -- -- 18.1 18.1 19.0 2,3,6
GL000254-341408 0.7269 -34.2357 98.9 -- -- 16.7 -- 17.2 -- -- -- -- -- 5
GL091049-085331 137.7050 -8.8919 27.7 20.0 19.3 -- 19.4 -- -- -- -- -- 18.7 2,3
GL223407+053413 338.5282 5.5703 65.5 19.9 18.9 -- 19.6 -- -- 17.4 17.9 17.5 -- 2,6
GL235624-312111 359.0995 -31.3532 125.1 -- -- -- -- -- -- -- -- -- 17.9 3
GL104703+263235 161.7609 26.5430 91.8 19.7 -- -- 19.0 -- -- -- -- -- 18.7 2,3
GL225138-053326 342.9087 -5.5573 53.2 19.9 19.4 -- 19.8 -- -- -- -- -- 19.2 2,3
GL225641-072245 344.1724 -7.3790 64.2 19.2 18.1 -- 18.5 -- -- -- -- -- -- 2
GL095230+020916 148.1235 2.1544 72.2 19.6 19.0 -- 18.7 -- -- -- -- -- 18.6 2,3
GL095730+080729 149.3742 8.1246 94.6 -- -- -- -- -- -- -- -- -- 19.0 3
GL103617+265744 159.0691 26.9623 92.1 19.5 19.1 -- 19.0 -- -- -- -- -- 19.1 2,3
GL234743-280838 356.9300 -28.1439 117.6 18.3 17.6 -- 23.8 -- -- -- -- -- -- 2
GL093635+010700 144.1473 1.1165 71.3 19.5 18.6 20.6 18.8 -- -- -- 16.2 -- -- 2,4
GL092056-094336 140.2319 -9.7268 56.4 -- -- -- -- -- -- -- -- -- 18.7 3
GL094617+054231 146.5710 5.7087 44.7 19.4 18.8 19.9 18.7 -- 17.1 -- 15.3 -- -- 7,2,4
GL094541+045631 146.4228 4.9419 54.0 19.9 19.2 -- 19.3 -- 17.9 -- -- -- -- 7,2
GL104245+265038 160.6860 26.8438 87.9 20.1 19.6 -- 19.4 -- -- -- -- -- 18.8 2,3
GL110427+381232 166.1138 38.2089 135.9 -- 18.2 -- 17.9 -- 18.1 -- -- -- 18.5 7,3
GL094901+041811 147.2530 4.3030 88.8 -- -- -- -- -- -- -- -- -- 18.6 3
GL094410+022437 146.0433 2.4103 86.7 20.1 19.3 -- -- -- -- -- -- -- -- 2
GL232149-164309 350.4551 -16.7192 85.6 18.6 17.6 -- 18.0 -- -- -- -- -- 19.0 2,3
GL230658-091710 346.7422 -9.2861 103.7 19.8 18.9 -- 19.1 -- -- -- 17.7 -- 18.8 2,3,6
GL101301+170203 153.2554 17.0342 95.9 19.3 19.0 20.6 18.9 17.2 -- -- 16.0 -- 18.6 5,2,4,3
GL093434+000522 143.6430 0.0894 68.4 19.9 19.5 18.6 19.7 17.9 -- -- -- -- 17.6 5,2,3
GL104827+263502 162.1140 26.5838 88.5 27.3 27.3 -- 27.3 -- -- -- -- -- 27.0 2,3
GL110558+362425 166.4920 36.4070 108.1 20.2 19.8 -- 19.5 -- -- -- -- -- 18.6 2,3
GL225544-062712 343.9352 -6.4533 104.7 19.9 19.2 -- 19.5 -- -- -- -- -- -- 2
GL100135+124554 150.3962 12.7649 91.2 19.8 19.3 -- 19.2 -- -- -- -- -- 18.8 2,3
GL235754-314854 359.4764 -31.8151 126.6 -- -- -- -- -- -- -- -- -- 18.0 3
GL100430+144608 151.1230 14.7690 101.5 19.3 18.6 20.0 18.4 -- -- -- 18.0 -- 14.3 4,2,3
GL100545+101636 151.4356 10.2767 104.9 -- -- -- -- -- -- -- -- -- 18.7 3
GL095757+102556 149.4862 10.4323 76.5 20.3 19.8 19.8 19.7 18.0 -- -- 15.8 -- -- 4,5,2
GL095905+102140 149.7714 10.3611 77.6 18.0 16.7 18.6 -- 18.0 -- -- -- -- -- 5,2
GL110759+352748 166.9957 35.4633 125.8 19.7 19.0 -- 19.0 -- -- -- -- -- 18.4 2,3
GL104739+261746 161.9130 26.2961 91.8 19.1 18.0 -- 18.3 -- -- -- -- -- 18.4 2,3
GL095351+085241 148.4630 8.8781 92.4 19.6 18.7 18.4 18.5 17.6 -- -- -- -- 18.8 2,3,5
GL232338-190035 350.9101 -19.0097 112.2 19.7 18.5 -- 19.1 -- -- -- -- -- 19.2 2,3
GL233923-222956 354.8438 -22.4989 112.9 19.2 18.9 -- 19.2 -- -- -- -- -- -- 2
GL120532+513017 181.3840 51.5047 124.3 20.4 19.7 -- 19.4 -- -- -- -- -- 18.8 2,3
GL110916+360116 167.3172 36.0212 92.7 19.9 19.1 -- 19.3 -- -- -- -- -- 18.1 2,3
GL230009-083953 345.0359 -8.6647 107.0 20.2 19.6 -- 19.6 -- -- -- -- -- -- 2
GL110505+352157 166.2693 35.3657 108.9 20.1 19.4 -- 19.1 -- -- -- -- -- 18.1 2,3
GL104552+255705 161.4677 25.9515 90.5 19.6 18.9 -- 18.5 -- -- -- -- -- 18.2 2,3
GL110955+365648 167.4810 36.9465 132.5 20.6 20.0 -- 19.7 -- -- -- -- -- 19.1 2,3
GL094900+022748 147.2477 2.4633 82.6 -- -- -- -- -- -- -- -- -- 14.5 3
GL102626+173038 156.6065 17.5105 80.7 -- -- -- -- -- -- -- -- -- 18.8 3
GL104607+255417 161.5305 25.9049 92.1 19.6 18.9 -- 18.5 -- -- -- -- -- 18.2 2,3
GL234615-280557 356.5627 -28.0990 121.6 -- 18.5 -- 18.8 -- -- -- -- -- -- 2
GL103139+255902 157.9119 25.9840 91.5 18.9 18.6 -- 18.2 -- 18.0 -- -- -- 19.1 7,2,3
GL102241+205133 155.6709 20.8590 107.4 -- -- -- -- -- -- -- -- -- 19.2 3
GL113253+433054 173.2190 43.5150 106.2 23.4 23.1 -- 19.6 -- -- -- -- -- 21.3 2,3
GL095106+090031 147.7751 9.0085 75.2 20.4 19.8 20.0 19.6 18.1 -- -- 17.7 -- 18.9 5,4,2,3
GL093744+024542 144.4330 2.7616 97.9 20.4 19.5 20.7 19.7 -- -- -- -- -- -- 2,4
GL091711-044508 139.2939 -4.7521 51.0 19.6 19.1 19.6 18.8 -- -- -- 17.4 -- 18.0 2,3,4
GL104642+255554 161.6770 25.9317 89.6 20.0 19.4 -- 19.0 -- -- -- -- -- 18.6 2,3
GL102917+260557 157.3200 26.0991 73.6 17.7 -- -- -- -- -- -- -- -- -- 2
GL110958+370810 167.4932 37.1360 113.7 20.2 -- -- 19.4 -- -- -- -- -- -- 2
GL111208+352707 168.0335 35.4520 108.8 20.2 18.8 -- 19.5 -- -- -- -- -- 17.9 2,3
GL094955+090949 147.4781 9.1637 75.6 18.2 17.3 19.7 17.1 15.5 -- -- 17.8 -- -- 5,2,4
GL100836+181353 152.1515 18.2313 73.9 -- -- 20.0 -- -- -- -- 18.2 -- -- 4
GL093411+001430 143.5440 0.2417 66.7 20.2 19.7 17.4 19.7 17.0 -- -- 17.2 -- 13.9 5,2,3,4
GL130847+621618 197.1938 62.2716 118.2 19.8 19.1 -- 18.8 -- -- -- -- -- 18.0 2,3
GL121329+504429 183.3722 50.7415 134.9 19.7 19.2 -- 19.0 -- -- -- -- -- -- 2
GL110542+350704 166.4263 35.1178 125.8 -- -- -- -- -- -- -- -- -- 17.9 3
GL233707-202747 354.2789 -20.4631 115.3 19.0 17.8 -- 18.2 -- -- -- -- -- -- 2
GL225223+010533 343.0941 1.0926 71.3 20.2 18.9 -- 19.2 -- -- -- -- -- -- 2
GL123208+562816 188.0340 56.4711 66.5 20.4 19.9 -- 22.2 -- -- -- -- -- 19.8 2,3
GL123221+563923 188.0891 56.6564 66.6 -- -- -- -- -- -- -- -- -- 17.9 3
GL120251+483811 180.7111 48.6363 49.4 20.1 19.7 -- 19.8 -- -- -- -- -- 18.2 2,3
GL110841+360940 167.1716 36.1610 121.1 -- -- -- -- -- -- -- -- -- 12.3 3
GL092046-080322 140.1927 -8.0562 85.6 -- -- -- -- -- -- -- -- -- 18.5 3
GL231645-185257 349.1889 -18.8825 109.5 19.2 -- -- 18.4 -- -- -- -- -- -- 2
GL130737+621258 196.9038 62.2160 121.1 20.2 19.7 -- 19.6 -- -- -- -- -- 17.9 2,3
GL104827+263501 162.1137 26.5837 91.4 27.3 27.3 -- 27.3 -- -- -- -- -- -- 2
GL120945+563125 182.4386 56.5235 115.1 -- -- -- -- -- -- -- -- -- 17.8 3
GL231022-084119 347.5910 -8.6886 103.0 18.3 17.2 -- 17.4 -- -- -- -- -- -- 2
GL091906-064215 139.7744 -6.7042 87.6 -- -- -- -- -- -- -- -- -- 17.6 3
GL113906+431450 174.7746 43.2473 106.3 20.4 19.9 -- 19.7 -- -- -- -- -- -- 2
GL123600+541315 189.0006 54.2208 77.6 20.2 19.4 -- 19.6 -- -- -- -- -- -- 2
GL111118+352308 167.8252 35.3855 108.8 20.1 19.3 -- 19.9 -- -- -- -- -- 18.1 2,3
GL225716-105700 344.3147 -10.9499 105.2 19.7 18.4 -- 18.9 -- -- -- -- -- -- 2
GL094953+090545 147.4705 9.0959 81.5 15.9 -- 19.7 -- 15.5 -- -- -- -- -- 5,4
GL114916+460713 177.3185 46.1203 94.5 -- -- -- -- -- -- -- -- -- 18.3 3
GL230009-124828 345.0368 -12.8079 50.6 20.1 19.1 -- 19.3 -- -- -- -- -- -- 2
GL114803+461028 177.0139 46.1746 108.5 -- -- -- -- -- -- -- -- -- 18.3 3
GL111451+353008 168.7137 35.5022 93.5 19.9 19.1 -- 19.2 -- -- -- -- -- 17.9 2,3
GL093745+024450 144.4378 2.7473 101.6 20.4 19.5 -- 19.7 -- -- -- -- -- -- 2
GL104532+240900 161.3845 24.1501 88.9 20.2 19.5 -- 19.0 -- -- -- -- -- -- 2
GL120446+491112 181.1925 49.1865 104.5 -- -- -- -- -- -- -- -- -- 17.9 3
GL111522+353007 168.8413 35.5020 92.4 19.9 19.1 -- 19.2 -- -- -- -- -- 17.9 2,3
GL111507+363224 168.7802 36.5401 107.1 20.2 19.3 -- 19.2 -- -- -- -- -- 18.2 2,3
GL103546+210253 158.9420 21.0481 102.5 17.5 -- 18.8 -- 18.0 -- -- -- -- 18.8 5,3
GL111535+363033 168.8966 36.5092 108.8 20.2 19.3 -- 19.2 -- -- -- -- -- 17.9 2,3
GL232235-130539 350.6470 -13.0941 102.5 19.9 18.9 -- 19.0 -- -- -- -- -- -- 2
GL112646+391558 171.6918 39.2662 90.6 -- -- -- -- -- -- -- -- -- 17.8 3
GL111734+360351 169.3902 36.0641 112.8 19.9 19.3 17.8 19.2 16.9 -- -- -- -- 17.8 2,3,5
GL094937+090019 147.4041 9.0053 75.4 18.9 18.1 15.9 17.8 15.5 -- -- 18.1 -- -- 5,2,4
GL111703+360828 169.2646 36.1411 110.5 20.3 19.6 17.8 19.6 16.9 -- -- -- -- -- 2,5
GL112719+383952 171.8290 38.6645 93.8 20.3 -- -- 19.2 -- -- -- -- -- 17.7 2,3
GL122635+525934 186.6451 52.9929 94.6 -- -- -- -- -- -- -- -- -- 18.2 3
GL112001+360603 170.0025 36.1007 110.3 20.5 19.6 -- 19.5 -- -- -- -- -- -- 2
GL113009+383713 172.5390 38.6204 93.3 -- -- -- -- -- -- -- -- -- 17.8 3
GL232407-115139 351.0290 -11.8607 108.1 19.7 18.6 -- 19.1 -- -- -- -- -- -- 2
References for obsid:
1: BAO101cm: 101 cm telescope at Bisei Astronomical Observatory and CCD optical camera (B, V, Rc, Ic)
2: Seimei-TriCCS: 380 cm Seimei telescope (g, r, i)
3: Kiso Schmidt: 105 cm Schmidt telescope at Kiso Observatory and Tomo-e Gozen 20 deg2 fov camera (no filter)
4: Kanata-HONIR: 150 cm Kanata telescope at Higashi-Hiroshima Observatory and HONIR -- a 2 channel imager (Rc and H or J) (Akitaya et al. 2014, Proc. SPIE 9147, 91474O)
5: MITSuME-Akeno: 50 cm MITSuME telescope at Akeno Observatory and a 3 color imager (g, Rc, Ic); The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ, 73, 1, 4-24; https://github.com/MNiwano/Eclaire).
6: Nayuta-NIC: 200 cm Nayuta telescope at Nishi-Harima Astronomical Observatory and Nishiharima Infrared Camera, NIC (J, H, Ks)
7: SaCRA-MuSaSHI: 55 cm SaCRA telescope at Saitama University and MuSaSHI (r, i, z) (Oasa et al., 2020, proc. SPIE, 11447, 114475Z)
GCN Circular 42724
A. Santos (CBPF), C. D. Kilpatrick (Northwestern), C. R. Bom (CBPF), L. Santana-Silva (CBPF), P. Darc (CBPF), Gabriel Teixeira (CBPF), C. Mendes de Oliveira (IAG-USP) report on behalf of the STEP-GW collaboration
Following the subsolar-mass gravitational-wave candidate S251112cm (GCN 42650, 42690), we conducted optical spectroscopic follow-up of four transients: 2025adiw, 2025adim, 2025adhf, and 2025adjf using the Goodman High-Throughput Spectrograph on the SOAR 4.1 m telescope at Cerro Pachón, Chile. Observations were performed on UT 2025 Nov 17 with the 400 l/mm M1 grating, 2×2 binning. For each source we obtained two 900 s exposures and coadded them for analysis. Each target was submitted for spectrum acquisition using the AEON queue. We classified 2025adim, 2025adiw, and 2025adhf as Type Ia supernovae based on SNID-SAGE spectral matches and identifiable SN Ia features. For 2025adjf, the spectra were heavily contaminated by host-galaxy light, preventing a definitive classification, and we instead report the host galaxy redshift based on nebular emission lines in the extracted spectrum. Our classification and redshift estimates are listed as follows:
| AT Name | Classification | redshift |
|---|---|---|
| 2025adim | SN Ia | 0.091 |
| 2025adiw | SN Ia | 0.165 |
| 2025adhf | SN Ia | 0.098 |
| 2025adjf | - | 0.124 |
All classified events are best matched to templates of normal or 91T-like SNe Ia at redshifts inconsistent with the expected distance for S251112cm, and thus are unlikely to be associated with the GW candidate. These results are based on observations obtained through the Astronomical Event Observatory Network (AEON), a joint endeavor of Las Cumbres Observatory and NSF NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the U.S. National Science Foundation.
GCN Circular 42722
Z. Y. Liu, W. Zhao, J.-A. Jiang, Z. L. Xu, D. Z. Meng, M. X. Cai, T. G. Wang, X. Kong, Z. G. Dai, L. L. Fan (USTC), Z. P. Jin, Y. Z. Fan (PMO) report on behalf of the WFST Collaboration:
Following the detection of the sub-solar mass merger candidate S251112cm (the LIGO-Virgo-Kagra Collaboration, GCN 42650), we conducted follow-up observations focused on the northern region of the initial bayestar skymap (GCN 42650) using the newly deployed 2.5-meter Wide Field Survey Telescope (WFST Collaboration; Wang et al., 2023) at the Lenghu Astronomical Observation Base (Qinghai province, China). Observations began at UTC 2025-11-13T11:29:36, corresponding to ~20.2 hours after the merger event (UTC 2025-11-12T15:18:45). The follow-ups lasted for three nights until UTC 2025-11-15T23:16:16. We observed in WFST g, r, and i bands with exposure times of 45-90 seconds. A total area of about 727.4 square degrees of the 90% skymap (GCN 42650) was observed, covering ~64% of the event localization. Additionally, ~7.5% skymap was covered in 30s g- and r-band exposures through the WFST wide-field survey (WFS) 6.35 hours after the merger event.
The follow-up observation data were processed using the WFST pipeline. For images localized in WFS, image subtraction was performed using the WFST stacking images taken berfore the event as templates. The search for the counterpart of S251112cm was performed mainly through visual inspection based on the locations of nearby galaxies, considering the distance estimate of 93 +/- 27 Mpc (redshift ~ 0.02; the LIGO-Virgo-Kagra Collaboration, GCN 42690) and the uncertainty of the potential electromagnetic counterpart. All extragalactic transient candidates detected by WFST during follow-ups were reported to the IAU Transient Name Server (TNS).
After excluding sources with pre-merger detections reported in TNS, only one candidate was found to be located near a galaxy with spectroscopic redshift below 0.045: AT2025aebp was first detected at 60992.93 (+1.3 days post-merger) with 21.5 +/- 0.1 mag in r-band, and the spectroscopic redshift of its possible host galaxy SDSS J103703.20+231142.2 is 0.043. Additionally, we report three other sources without pre-merger detections. These sources have possible host galaxies with SDSS DR16 photometric redshift (Csabai et al., 2007; Ahumada et al., 2019) less than 0.1:
| AT Name | MJD | RA | Dec | Filter | Mag | Host | photoZ |
|---|---|---|---|---|---|---|---|
| AT2025aebk | 60992.86 | 156.5043 | 24.9277 | g | 21.8 ± 0.1 | SDSS J102601.47+245542.1 | 0.06 ± 0.02 |
| AT2025aebl | 60992.92 | 152.3554 | 18.2025 | r | 21.4 ± 0.1 | SDSS J100925.32+181207.3 | 0.09 ± 0.03 |
| AT2025aebq | 60992.94 | 172.3128 | 36.6438 | r | 21.4 ± 0.1 | SDSS J112914.78+363832.0 | 0.09 ± 0.03 |
We also checked the aforementioned candidates reported through TNS and GCN Circulars (GCN 42658, GCN 42666, GCN 42677, GCN 42691, GCN 42707). Ten public sources were detected in our difference images. Difference photometric results are listed as follows:
| AT Name | MJD | RA | Dec | Filter | Mag |
|---|---|---|---|---|---|
| AT2025adjd | 60992.96 | 190.8110 | 56.8036 | r | 21.31 ± 0.04 |
| AT2025adie | 60992.83 | 185.3958 | 56.5862 | g | 21.7 ± 0.1 |
| AT2025adhu | 60992.83 | 181.8041 | 55.6536 | g | 21.4 ± 0.1 |
| AT2025adtj | 60990.94 | 172.5489 | 38.6207 | r | 19.64 ± 0.03 |
| AT2025adia | 60992.85 | 169.5689 | 35.9858 | g | 21.6 ± 0.1 |
| AT2025adln | 60989.89 | 168.0373 | 30.42659 | g | 21.2 ± 0.2 |
| AT2025adlk | 60989.93 | 159.2667 | 19.30616 | g | 20.1 ± 0.1 |
| AT2025adic | 60989.89 | 169.5444 | 41.0946 | g | 21.8 ± 0.2 |
| AT2025adtq | 60990.94 | 175.6142 | 34.0085 | r | 21.2 ± 0.1 |
| AT2025adtk | 60990.93 | 174.3825 | 31.3606 | r | 18.98 ± 0.02 |
We thank the WFST staff for supporting these observations. Subsequent WFST observations and a systematic search for potential transients are ongoing.
GCN Circular 42714
Q. Y. Wu, J. W. Hu, Y. Liu (NAO, CAS), B. Zhang (HKU) on behalf of the Einstein Probe (EP) team:
EP-FXT performed a series of follow-up observations of the LIGO/Virgo/KAGRA gravitational-wave event S251112cm (GCN 42650, GCN 42690), with 100 galaxy-targeted observations have been completed. These observations were conducted from 2025-11-12T15:38:36 to 2025-11-14T10:28:28 (UTC), with each pointing having an exposure of approximately 300 s. EP-FXT covered 88 deg2 (8.9% in probability) of the updated sky localization area (GCN 42690)
We cross-matched all FXT detections from these pointings against the updated list of NED galaxies provided in GCN 42693, using a 100″ matching radius (for a galaxy at 100 Mpc this corresponds to an offset of ~50 kpc). Most matched sources have prior X-ray detections with FXT fluxes comparable to historical values. There are two weak sources without prior X-ray counterparts within the FXT error region. Their information is summarized below (RA/Dec in degrees with 10" error radius (90% C.L.); fluxes are the observed ones in 0.5–10 keV):
Name | RA | Dec | Matched NED Galaxy | Sep. (arcsec) | Flux (erg/s/cm^2) | SNR
----------------------------------------------------------------------------------------------------------------------------
EPF_J234847.8-282639 | 357.1990 | -28.4442 | WISEA J234841.30-282641.1 | 85.2 | 7.4e-13| 6.6
EPF_J010845.7-463304 | 17.1904 | -46.5512 | SMDG J0108452-463428 | 83.8 | 1.4e-13| 4.2
In addition, FXT detected 8 sources with no prior X-ray detections, no matches to the NED galaxies and no obvious AGN or stellar counterparts within the FXT error regions. Their information is summarized below (RA/Dec in degrees with 10" error radius (90% C.L.); fluxes are the observed ones in 0.5–10 keV):
Name | RA | Dec | Flux (erg/s/cm^2) | SNR
-------------------------------------------------------------------------
EPF_J000245.6-341925 | 0.6899 | -34.3235 | 2.0e-13| 4.0
EPF_J020544.2-520424 | 31.4343 | -52.0734 | 1.7e-13| 4.1
EPF_J092041.9-081815 | 140.1746 | -8.3041 | 2.1e-13| 4.9
EPF_J093255.2-020027 | 143.2301 | -2.0076 | 4.3e-13| 3.5
EPF_J111043.0+362227 | 167.6792 | 36.3742 | 1.6e-13| 4.6
EPF_J113825.2+432218 | 174.6051 | 43.3716 | 7.3e-14| 5.4
EPF_J232328.1-114600 | 350.8670 | -11.7667 | 1.5e-13| 3.9
EPF_J234628.3-290057 | 356.6177 | -29.0158 | 7.9e-13| 4.5
Further FXT observations of these candidates will be conducted.
Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).
GCN Circular 42707
Sean MacBride (University of Zurich), Erin Howard, Ian Sullivan, Peter Yoachim, Eric Bellm (University of Washington), Shreya Anand (Stanford University), Federica Bianco (University of Delaware), Tiago Ribeiro, Lynne Jones, Alysha Shugart, Narayan Khadka, Kshitija Kelkar, Danica Zilkova, Kevin Fanning, Paulina Venegas, Kate Napier, Erik Dennihy, Anastasia Alexov, Bob Blum (NSF-DOE Vera C Rubin Observatory), Yousuke Utsumi (National Astronomical Observatory of Japan), Robert Lupton (Princeton University), Keith Bechtol (University of Wisconsin-Madison), reporting on behalf of NSF-DOE Vera C Rubin Observatory:
We observed the localization region of the sub-solar mass merger S251112cm, reported by LIGO/Virgo/KAGRA (GCN 42650, GCN 42690) with the 9.6 square degree field of view LSST Camera mounted on the 8.4-m Simonyi Survey Telescope at the Vera C. Rubin Observatory. As reported in GCN 42690, S251112cm has a reported 90% localization area of 1681 square degrees and an expected false alarm rate of approximately one in four years. This is the first Target-of-Opportunity observation with Rubin Observatory since the transition to operations in late October 2025.
Rubin Observatory is in an early operations period of continued system optimization, prior to beginning sustained LSST observations [1]. During this period, data quality and acquisition rate are variable. Not all data products that will be available during the Legacy Survey of Space and Time (LSST) operations are currently available [2].
Observations were conducted through engagement of the new Rubin Target-of-Opportunity advisory board, as a sub-solar mass merger does not meet the typical alert quality criteria for Rubin Target-of-Opportunity (ToO) observation [3]. The observing strategy for this event is to image the localization area in LSST g and i bands, with one 30 second visit for each band, on nights 0, 2, 4, and 6 of the observing campaign.
On November 15 2025, at 01:49:27 UTC, we began observing the localization region of S251112cm, using the initial localization information provided in GCN 42650. We observed 39.2% (849.1 deg^2) of the localization area in the g-band, and 33.5% (754.9 deg^2) of the localization area in the i band. The difference in coverage was due to the localization area of S251112cm setting early in the night in Chile, before the telescope could observe the region in i band. For these observations, we reached a median depth of 24.8 mag in g band, 23.7 mag in the i band.
Due to the lack of prior Rubin observations in most of the imaging area, we performed image differencing against DECam templates. To support the usage of DECam templates, we devised a custom image processing task to create DECam templates from DES templates for use with LSSTCam observations. Apart from the DECam template task, we utilize the standard LSST data release production pipeline to obtain difference images and photometry on difference image sources [4].
With only a single epoch of observations at Rubin Observatory, we are unable to characterize viable candidates from Rubin observations alone. Here, we report on candidates reported in GCN 42658, 42663, 42666, 42675, 42677, 42681, 42682, and 42691. We do not recover several candidates from these GCN’s for one of many reasons: lack of signal in the difference images, poor image subtraction near the source, or a lack of imaging in the region. Here, we report the candidates that pass these criteria, and comment on any notable nearby galaxies, given the reported luminosity distance from LVK (GCN 42650).
We perform visual inspection on difference images that are coincident with previously reported candidates. We positively detect AT2025adgq, AT2025adhf, AT2025adkl, AT2025adjp, and AT2025addc. AT2025adhf and AT2025adkl were only detected unambiguously in one band (g and i respectively). Whether they are not detected in the other band is still under investigation.. AT2025adgq is detected unambiguously in two bands, separated from a host galaxy by ~10 arcseconds. AT2025adhf is nuclear to a barred spiral galaxy (WISEA J024344.38-551906.1), but its WISE colors are not consistent with the host being an AGN. AT2025adkl is offset by 90’ from a galaxy within the NED volume (GCN 42653), slightly offset from a small distant galaxy, and detected unambiguously in one band. AT2025adjp and AT2025addc are isolated sources detected unambiguously in two bands.
Here we report difference photometry for the aforementioned candidates:
| AT Name | Observation Date [UTC] | RA | Dec | g | unc_g | i | unc_i |
|---|---|---|---|---|---|---|---|
| AT2025adgq | 2025-11-15 | 7.3825 | -39.5143 | 19.55 | 0.005 | 19.52 | 0.003 |
| AT2025adhf | 2025-11-15 | 40.9351 | -55.3184 | - | - | 19.21 | 0.004 |
| AT2025adkl | 2025-11-15 | 7.5357 | -41.0787 | 21.58 | 0.014 | - | - |
| AT2025adjp | 2025-11-15 | 4.5396 | -33.8543 | 21.17 | 0.010 | 20.90 | 0.016 |
| AT2025addc | 2025-11-15 | 73.8589 | -53.1621 | 20.91 | 0.009 | 21.25 | 0.022 |
Analysis of these candidates is ongoing. We will continue to observe the localization area of S251112cm in the coming days according to the observing plan.
We thank all who contributed to the design and implementation of the Vera C. Rubin Observatory Target-of-Opportunity system, including but not limited to, the LSST Transients and Variable Stars Science Collaboration Multiwavelength Characterization and Counterparts subgroup. We especially thank the Rubin Observatory observers, who are instrumental to the performance and success of the LSST.
This material is based upon work supported in part by the National Science Foundation through Cooperative Agreements AST-1258333 and AST-2241526 and Cooperative Support Agreements AST-1202910 and 2211468 managed by the Association of Universities for Research in Astronomy (AURA), and the Department of Energy under Contract No. DE-AC02-76SF00515 with the SLAC National Accelerator Laboratory managed by Stanford University. Additional Rubin Observatory funding comes from private donations, grants to universities, and in-kind support from LSST-DA Institutional Members.
[1] sitcomtn-005.lsst.io, §6
[2] lse-163.lsst.io
[3] www.inspirehep.net/literature/2846480
[4] pstn-019.lsst.io
GCN Circular 42699
P. Hello (IJCLAB), D. Akl (NYUAD), S. Antier (IJCLAB), A. Klotz (IRAP), M. Mazek (FZU), M. Pillas (IAP), O. Pyshna (Caltech), C. Andrade (UMN), M. Coughlin (UMN), C. Douzet (IJCLAB), S. Karpov (FZU), T. duLaz (Caltech), R. LeMontagner (IJCLAB), C. Limonta (OCA), Y. Rajabov (UBAI), D. Turpin (CEA-AIM) on behalf of the GRANDMA collaboration:
We observed the S251112cm (Initial, as provided by GCN 42650, LVK collaboration) sky localization area with wide field telescopes TAROT/TRE, TAROT/TCH, TAROT/TCA, FRAM-FZU,together with the 60 cm telescope at Les Makes Observatory. Observations started at 2025-11-12 17:14 UTC, e.g 1h56 after the trigger time and during 14h. We used the SkyPortal application (skyportal.io) and associated services to monitor this observational campaign (Coughlin et al. 2018, 2023).
Our sensivity map of the GW sky localization area has been computed using Pillas et al., 2025 and is accessible at https://grandma-owncloud.ijclab.in2p3.fr/index.php/s/TqGach7PpbM4d3K.
We covered 22% of the Initial sky localization area (Bayestar, GCN 42650 LVK collaboration) and 16% of the Updated sky localization area (Bilby, GCN 2690, LVK collaboration). Preliminary analysis did not reveal any clear candidate that can be associated to the event (with limit magnitudes ranging from 17 to 21 mag in r-band at 5 sigma). We re-conducted a second epoch of observations the day after.
All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2025). Images obtained were calibrated using the PanSTARRS DR1 catalog.
We are currently investigating candidates reported by other collaborations.
GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/).
GCN Circular 42698
O. Burkhonov, Y. Rajabov, Y. Tillayev (UBAI), P. Hello (IJCLAB), A. Klotz (IRAP), M. Coughlin (UMN), S. Karpov (FZU), M. Pillas (IAP), M. Mazek (FZU ), S. Antier (IJCLAB), O. Pyshna (Caltech) on behalf of GRANDMA:
We detected transient event 2025adht in RA_J2000=12:00:24.3431, Dec_J2000=+49:02:51.7 reported by (GCN 42677 Anand et al., Franz GCN 42675 et al.,). Observations were carried out at the 1.5-meter telescope Maidanak Observatory by using 4Kx4K SNUCAM CCD. All observations were taken using a Bessel R filter. The observations started at 2025-11-15T00:13:15 UTC and ended at 2025-11-15T00:40:17 UTC. A total of 6 CCD images with an exposure of 300 seconds were obtained.
Despite the fact that this object is located far from the equator, we checked for the presence of small bodies in this region using the small body database from 14 November 2025. The check was negative. Cross-identification results indicated the same galaxy without any transient events: DSS J120024.56+490254.3, WISEA J120024.53+490254.1, and GALEXASC J120024.49+490252.9.
We analyzed our data using our standard pipeline and with STDWeb/STDPipe (Karpov, 2025). We present stacked results after galaxy soustraction.
MJD | DATE-OBS | MAG |M_ERR|U.L.|FILTER| Telescope| MAG system
--------------------------------------------------------------------------------------
60994.00920139 | 2025-11-15 00:29 | 21.54|0.1|22.10|R|UBAI/AZT-22|Vega, Gaia DR3
Which has an equivalent using PS1 of 21.64+/- 0.1 in sdssr using PS1 (color term 0.13).
More observations are planned.
GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/). Maidanak astronomical observatory (MAO) is an observational facility of the Ulugh Beg Astronomical Institute (UBAI), Uzbekistan Academy of Sciences (http://maidanak.uz/).
GCN Circular 42693
David O. Cook (Caltech/IPAC), Rick Ebert (Caltech/IPAC), George Helou (Caltech/IPAC), Joseph M. Mazzarella (Caltech/IPAC), Marion Schmitz (Caltech/IPAC), and Leo Singer (NASA/GSFC)
On behalf of the NASA/IPAC Extragalactic Database (NED) Team.
We spatially cross-matched the LVK S251112cm-4-Update sky localization with the NED Local Volume Sample (NED-LVS; Cook et al. 2023; https://ned.ipac.caltech.edu/NED::LVS/), which is a subset of NED with a redshift or redshift-independent distance less than 1000 Mpc. We find 9047 galaxies within the 90% containment volume, and we list here the top 20 galaxies sorted by the joint probability of the 3D localization and the WISE W1 luminosity (an observable proxy for stellar mass). For the full or top 20 list of galaxies in the 90% volume go either to the NED Gravitational Wave Followup service at https://ned.ipac.caltech.edu/uri/NED::GWF/ or click on the following links:
Full List Download: https://ned.ipac.caltech.edu/uri/NED::GWFglist/fits/S251112cm/4
Top 20 List Download: https://ned.ipac.caltech.edu/uri/NED::GWFglist/fits/S251112cm/4/20
The NED-GWF service provides downloadable galaxy lists and visualizations for candidate host galaxies. For each GW alert, these products are automatically generated and made available within minutes to expedite efficient electromagnetic follow-up observations. The NED top 20 list is sorted by the joint probability of the 3D localization and the WISE W1 luminosity, but users can sort on additional pre-computed prioritization metrics (star formation rate, P_3D * P_SFR; and specific star formation rate, P_3D * P_sSFR; etc.) which are available via downloading the entire galaxy list inside the event's probability volume.
| objname | ra | dec | objtype | DistMpc | DistMpc_unc | m_NUV | m_NUV_unc | m_Ks | m_Ks_unc | m_W1 | m_W1_unc | P_3D | P_3D_LumW1 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| IC 1633 | 17.48145 | -45.93116 | G | 96.06 | 3.43 | null | null | 8.396 | 0.025 | 8.999 | 0.006 | 8.02e-06 | 1.10e-08 |
| IC 0564 | 146.58792 | 3.07130 | G | 75.75 | 2.62 | null | null | 10.033 | 0.035 | 10.010 | 0.006 | 2.41e-05 | 8.10e-09 |
| IC 1464B | 345.79587 | -8.98909 | G | 105.88 | 0.59 | null | null | 10.015 | 0.036 | 9.741 | 0.006 | 8.31e-06 | 6.98e-09 |
| WISEA J100012.04+093856.0 | 150.05020 | 9.64890 | G | 78.82 | 0.30 | null | null | 11.073 | 0.096 | 10.233 | 0.006 | 2.04e-05 | 6.04e-09 |
| UGC 05226 | 146.51479 | 4.40348 | G | 66.86 | 15.78 | 18.763 | 0.092 | 10.211 | 0.041 | 10.083 | 0.089 | 2.21e-05 | 5.42e-09 |
| ESO 197- G 021 | 31.13585 | -52.17213 | G | 87.54 | 0.39 | null | null | 9.099 | 0.026 | 9.375 | 0.006 | 6.49e-06 | 5.21e-09 |
| MCG -01-24-010 | 140.09147 | -7.88074 | G | 53.94 | 2.54 | 15.885 | 0.007 | 10.054 | 0.032 | 9.821 | 0.030 | 2.49e-05 | 5.05e-09 |
| MRK 0421 | 166.11381 | 38.20883 | G | 85.15 | 33.84 | null | null | 9.996 | 0.029 | 9.258 | 0.005 | 5.81e-06 | 4.92e-09 |
| IC 1464A | 345.80030 | -8.99285 | G | 107.09 | 0.04 | null | null | 11.963 | 0.011 | 10.070 | 0.006 | 7.57e-06 | 4.81e-09 |
| NGC 7364 | 341.10153 | -0.16213 | G | 76.48 | 8.25 | 16.366 | 0.001 | 9.478 | 0.028 | 9.218 | 0.003 | 6.74e-06 | 4.80e-09 |
| IC 1471 | 347.18676 | -12.63948 | G | 83.00 | 17.58 | 17.246 | 0.027 | 10.334 | 0.035 | 10.290 | 0.006 | 1.49e-05 | 4.63e-09 |
| ESO 243- G 051 | 17.83050 | -45.93204 | G | 94.78 | 0.36 | 17.032 | 0.008 | 10.015 | 0.031 | 10.036 | 0.006 | 8.85e-06 | 4.53e-09 |
| NGC 2951 NED01 | 144.92019 | -0.23515 | G | 70.23 | 0.53 | 18.380 | 0.003 | 10.498 | 0.057 | 10.537 | 0.004 | 2.33e-05 | 4.19e-09 |
| IC 2471 | 141.30071 | -6.82994 | G | 58.50 | 12.39 | 18.644 | 0.054 | 9.949 | 0.034 | 10.076 | 0.006 | 2.19e-05 | 4.12e-09 |
| NGC 3070 | 149.52893 | 10.35980 | G | 60.25 | 5.89 | 18.225 | 0.068 | 9.260 | 0.030 | 9.503 | 0.006 | 1.21e-05 | 4.12e-09 |
| ESO 197- G 018 | 30.62846 | -50.93160 | G | 110.00 | 24.82 | null | null | 9.612 | 0.028 | 9.779 | 0.006 | 4.35e-06 | 3.80e-09 |
| NGC 2951 NED02 | 144.91664 | -0.23524 | G | 71.31 | 0.04 | 18.383 | 0.003 | 12.873 | 0.052 | 10.592 | 0.004 | 2.13e-05 | 3.75e-09 |
| ESO 243- G 045 | 17.26888 | -45.77349 | G | 82.00 | 9.44 | 18.245 | 0.024 | 9.713 | 0.035 | 9.964 | 0.006 | 9.07e-06 | 3.71e-09 |
| IC 0563 | 146.58473 | 3.04574 | G | 57.00 | 22.05 | 16.948 | 0.010 | 10.810 | 0.054 | 10.328 | 0.027 | 2.54e-05 | 3.62e-09 |
| ESO 197- G 010 | 28.30237 | -49.56039 | G | 76.43 | 6.54 | null | null | 8.882 | 0.034 | 9.458 | 0.006 | 6.17e-06 | 3.50e-09 |
Table 1: Top 20 galaxies in NED-LVS that fall in the 90% probability volume for S251112cm sorted by the joint probability of 3D position and WISE W1 luminosity (P_3D * P_LumW1). Galaxy is the NED preferred name. RA and Dec are the Equatorial coordinates in degrees (J2000). Objtype is the object type of the galaxy candidate. Distance is the distance to the galaxy in Mpc. m_NUV and mErr_NUV are the apparent magnitude and error from GALEX. m_Ks and mErr_Ks are the apparent magnitude and error from 2MASS. m_W1 and mErr_W1 are the apparent magnitude and error from AllWISE. P_3D is the probability that the galaxy is in the volume given the distance of GW event. P_3D_LumW1 is the joint probability within the volume weighted by the WISE1 luminosity of the galaxy (P_3D * P_LumW1).
GCN Circular 42691
Xander J. Hall (CMU), Tomás Cabrera (CMU), Julius Gassert (CMU/LMU), Lei Hu (UPenn), Antonella Palmese (CMU), Brendan O’Connor (CMU), Igor Andreoni (UNC), on behalf of the Gravitational Wave MultiMessenger Astronomy DECam Survey (GW-MMADS) team report:
We observed the high probability area of the LVK gravitational wave candidate S251112cm (GCN 42650) using the wide-field Dark Energy Camera (DECam) on the 4m Blanco telescope. Observations started at 2025-11-14 00:03 UTC (Prop ID: 2023B-851374; PI Palmese & Andreoni) and focused on the southern lobe of the Bilby skymap (GCN 42690; 30% of the total posterior probability).
We run the SFFT difference imaging (Hu et al. 2022) on the available images, filter out likely stars and moving objects, and then visually inspect the remaining transients. We report on TNS 54 new transients within the observed area, and we report here select transients:
| id | AT name | ra | dec | discovery_date (UT) | mag_g | mag_g_err | mag_g-mag_i | NED separation |
|---|---|---|---|---|---|---|---|---|
| T202511140018095m335115* | AT 2025adjp | 4.539622 | -33.854284 | 2025-11-14 02:08:26.016 | 21.13 | 0.04 | 0.25 | 92.7", 94.5", 94.6" |
| T202511140030086m410443 | AT 2025adkl | 7.535766 | -41.078709 | 2025-11-14 02:13:43.104 | 20.91 | 0.03 | -0.14 | 90.5" |
*This transient is within 2' of three NED in-volume galaxies.
We note while both of these transients are within 2' of a NED in-volume galaxy (GCN 42653), they are both near galaxies with LS DR9 photo-z > 0.12 which would place them outside of the volume.
Further analysis is underway.
We thank the CTIO and NOIRLab staff for supporting these observations and the data calibration.
GCN Circular 42690
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We have conducted further analysis of the LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S251112cm (GCN Circular 42650). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,1, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page:
https://gracedb.ligo.org/superevents/S251112cm
For the Bilby.multiorder.fits,1 sky map, the 90% credible region is 1681 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 93 +/- 27 Mpc (a posteriori mean +/- standard deviation).
The false alarm rate, as estimated by the MBTA SSM analysis pipeline with an updated background model, has been updated to about one in 4 years.
The online search for sub-solar-mass regions is covered by two independent pipelines: MBTA SSM and GstLAL SSM [2]. For the parameter space relevant to the present candidate, only MBTA SSM provides online coverage; therefore, the candidate was triggered solely by MBTA SSM.
For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/.
[1] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. PRD 108, 123040 (2023) doi:10.1103/PhysRevD.108.123040
[2] https://emfollow.docs.ligo.org/userguide/analysis/index.html#false-alarm-rate-for-alerts-and-trials-factor
GCN Circular 42682
A. Smith, M. Nicholl, (QUB), J. Gillanders, S. J. Smart, K. W. Smith, (Oxford), D. R. Young, C. R. Angus, M. D. Fulton, T. Moore, A. Aamer, S. Sim, J. Weston, X. Sheng, D. Magill, P. Ramsden (QUB), S. Srivastav, H. Stevance, F. Stoppa, A. Cooper, J. Tweddle, L. Eastman (Oxford), L. Shingles (GSI/QUB), L. Rhodes (TSI/McGill), L. Denneau, J. Tonry, H. Weiland, R. Siverd (IfA, University of Hawaii), N. Erasmus, W. Koorts (South African Astronomical Observatory), A. Rest (STScI), T.-W. Chen (NCU), C. Stubbs (Harvard), J. Sommer (LMU/QUB), B. Schmidt (ANU):
We report observations of the Bilby.fits skymap of the compact binary merger candidate S251112cm (The LIGO-Virgo-Kagra Collaboration, GCN 42650) with the ATLAS telescope system (Tonry et al., 2018, PASP, 13, 164505). ATLAS is a quintuple 0.5m optical telescope survey system (Hawaii x 2, South Africa, Chile, Tenerife) employing three filters, cyan, orange, and ‘clear’. In our primary NASA mission for Near-Earth Object discovery, we cover the entire visible night sky every 24hrs to AB magnitude depths m ~ 19.5, weather and Moon permitting.
During focused science operations, we covered part of the accessible skymap of S251112cm. A sequence of quads (4 x 120-sec images) was taken at each pointing position. The images were processed with the ATLAS pipeline, and reference images were subtracted from each one. Transient candidates were identified and run through our standard filtering procedures (Smith et al., 2020, PASP, 132, 1). We covered 665.14 square degrees of the bilby.fits skymap 90% area, and covered a sky region totalling 45.08% of the event's full localisation likelihood, South of declination = 11 degrees. Data acquisition began at MJD 60991.811354 or 2025-11-12 19:28:20 (UTC), 3.5hrs after the LVC Preliminary/Initial notice and 4.2hrs after the merger event at 2025-11-12 15:18:45.362 (UTC).
Observations lasted between ~4.2hrs to 41.3hrs after the GW detection. The depths of our images typically reached m_o < 19.5 AB mag. We found 26 transient sources, including 5 previously unreported transients. However, all had been previously detected by ATLAS before the merger event, or reported to the IAU Transient name server (https://www.wis-tns.org) and/or are associated with host galaxies with photometric redshifts beyond z > 0.05. We are reporting all discoveries to the TNS, where they can be tracked, classified, searched, and commented upon. We encourage further information to be reported on the TNS object pages.
We checked the ATLAS forced photometry for the 3 GOTO objects reported by Ackley et al. (GCN 42658), and confirmed that all three have flux detected before the S251112cm GW event time. This flux on the individual 30 sec images are each below 5-sigma significance but the combined detections over multiple nights indicate the source was detected. These detections can be checked on ATLAS forced photometry server (Shingles et al. AstroNote 2021-7).
The Asteroid Terrestrial-impact Last Alert System (ATLAS) project is primarily funded to search for Near-Earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from the survey area. This work was partially funded by Kepler/K2 grant J1944/80NSSC19K0112 and HST GO-15889, and STFC grants ST/T000198/1 and ST/S006109/1. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen's University Belfast, the University of Oxford, the Space Telescope Science Institute, the South African Astronomical Observatory, and The Millennium Institute of Astrophysics (MAS), Chile.
GCN Circular 42681
K.L. Page (U. Leicester), P.A. Evans (U. Leicester), J.A. Kennea (PSU), A.
Tohuvavohu (Cosmic Frontier Labs), S.B. Cenko (NASA/GSFC), R.A.J. Eyles-Ferris (U.
Leicester), A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), A.A. Breeveld
(UCL-MSSL), S. Campana (INAF-OAB), J.J. Delaunay (PSU), M. De Pasquale (University
of Messina), S. Dichiara (PSU), P. D’Avanzo (INAF-OAB), A. D’Aì (INAF-IASFPA) ,
V. D’Elia (ASI-SSDC & INAF-OAR), C. Gronwall (PSU), D. Hartmann (Clemson
University), N. Klingler (NASA-GSFC / UMBC / CRESST II), N.P.M. Kuin (UCL-MSSL), S.
Laha (NASA/GSFC), S.R. Oates (U. Birmingham), J.P. Osborne (U. Leicester), P.
O’Brien (U. Leicester), M.J. Page (UCL-MSSL), G. Raman (PSU) S. Ronchini (PSU), T.
Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.H. Siegel (PSU), G. Tagliaferri
(INAF-OAB), E. Troja (U Tor Vergata, INAF) report on behalf of the Swift team:
Swift has carried out 105 observations of the LVK error region for the GW trigger
S251112cm convolved with the 2MPZ catalogue (Bilicki et al. 2014, ApJS, 210, 9),
using the 'BAYESTAR' (version BAYESTAR.fits.gz) GW localisation map. As this is a 3D
skymap, galaxy distances were taken into account in selecting which ones to observe.
The observations currently span from 7.6 ks to 117 ks after the LVK trigger, and the
XRT has covered 12.7 deg^2 on the sky (corrected for overlaps). This covers 1.3% of
the probability in the 'BAYESTAR' (version BAYESTAR.fits.gz) skymap, and 20% after
convolving with the 2MPZ galaxy catalogue, as described by Evans et al. (2016,
MNRAS, 462, 1591).
We have detected 20 X-ray sources. Each source is assigned a rank of 1-4 which
describes how likely it is to be related to the GW trigger, with 1 being the most
likely and 4 being the least likely. The ranks are described at
https://www.swift.ac.uk/ranks.php.
We have found:
* 0 sources of rank 1
* 0 sources of rank 2
* 7 sources of rank 3
* 13 sources of rank 4
RANK 3 sources
==============
These are uncatalogued X-ray sources, however they are not brighter than previous
upper limits, so do not stand out as likely counterparts to the GW trigger.
| Source ID | RA | Dec | Err90 | Detection Flag |
| S251112cm_X1 | 11 09 55.90 | +36 08 20.7 | 8.0" | POOR |
| S251112cm_X38 | 23 47 03.18 | -28 07 08.2 | 9.5" | POOR |
| S251112cm_X53 | 11 08 18.65 | +36 11 04.6 | 8.1" | POOR |
| S251112cm_X72 | 12 22 09.27 | +55 52 20.4 | 5.9" | GOOD |
| S251112cm_X73 | 01 08 29.26 | -46 59 48.1 | 8.9" | POOR |
| S251112cm_X78 | 23 48 35.23 | -28 14 05.5 | 9.8" | POOR |
| S251112cm_X79 | 23 48 06.04 | -28 04 35.1 | 12.3" | POOR |
RANK 4 sources
==============
These are catalogued X-ray sources, showing no signs of outburst compared to
previous observations, so they are not likely to be related to the GW trigger.
| Source ID | RA | Dec | Err90 | Detection Flag |
| S251112cm_X2 | 11 12 06.93 | +35 27 45.6 | 6.8" | GOOD |
| S251112cm_X3 | 09 20 46.26 | -08 03 21.4 | 5.5" | GOOD |
| S251112cm_X5 | 23 51 37.99 | -28 18 18.1 | 7.6" | POOR |
| S251112cm_X50 | 11 37 24.49 | +47 27 44.7 | 7.4" | GOOD |
| S251112cm_X51 | 01 08 20.79 | -47 07 36.3 | 7.4" | POOR |
| S251112cm_X52 | 01 07 42.60 | -46 54 24.5 | 6.1" | GOOD |
| S251112cm_X67 | 11 11 04.66 | +35 13 59.3 | 6.9" | GOOD |
| S251112cm_X68 | 22 44 47.97 | -00 06 17.5 | 8.8" | GOOD |
| S251112cm_X69 | 02 36 19.70 | -54 51 50.8 | 5.8" | GOOD |
| S251112cm_X70 | 13 06 57.05 | +59 58 48.1 | 10.7" | REASONABLE |
| S251112cm_X71 | 12 23 00.00 | +55 40 04.4 | 5.1" | GOOD |
| S251112cm_X87 | 11 12 01.25 | +37 58 26.3 | 6.1" | GOOD |
| S251112cm_X88 | 11 04 27.52 | +38 12 36.6 | 3.5" | GOOD |
For all flux conversions and comparisons with catalogues and upper limits from other
missions, we assumed a power-law spectrum with NH=3x10^20 cm^-2, and photon index
(Gamma)=1.7, unless otherwise stated.
The results of the XRT automated analysis, including details of the sources listed
above, are online at https://www.swift.ac.uk/LVC/S251112cm
This circular is an official product of the Swift XRT team.
GCN Circular 42677
S. Anand (Stanford), R. Stein (UMD), X. J. Hall (CMU), V. Swain (IIT-B), A. Saikia (IIT-B), T. Mohan (IIT-B), V. Bhalerao (IIT-B), D. Cook (Caltech/IPAC), A. Singh (SU), M. M. Kasliwal (Caltech), E. C. Bellm (UW), M. Coughlin (UMN), T. du Laz (Caltech), V. Karambelkar (Columbia), G. Waratkar (Caltech), I. Andreoni (UNC), A. Palmese (CMU) report,
on behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations:
We observed the localization region of the LVK sub-solar mass candidate S251112cm (GCN 42650) with the Palomar 48-inch telescope, equipped with the 47 square degree ZTF camera (Bellm et al. 2019, Graham et al. 2019). We started observations in the g- and r-band beginning at 2025-11-12 09:21 UTC, approximately 18 hours after merger, covering 38.3% of the probability within the 90% credible region of the LVK skymap in g- and r-bands. This estimate accounts for chip gaps. Each exposure was 300s with a median r-band depth of 21.14 mag.
The images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts (Masci et al. 2019). AMPEL (Nordin et al. 2019, Stein et al. 2021) was used to search the alerts database for candidates. We reject stellar sources (Tachibana and Miller 2018) and moving objects, and apply machine learning algorithms (Mahabal et al. 2019), removing candidates with history of variability prior to the merger time.
Because of the nature of the GW trigger as a sub-solar mass merger candidate, we do not exclude any candidates that may be consistent with being young stripped envelope supernovae (SESNe). Disk fragmentation or core fissioning in SESNe may lead to the formation of subsolar mass neutron stars (Metzger et al. 2024, Kasliwal et al. 2025).
After filtering, 8 transient candidates remain, all within the 95.0% localization of the skymap. Candidates marked as FAR have redshifts from Legacy Survey or from SDSS (shown below). Redshift lower limits come from Legacy Survey (l95; a conservative lower limit on the photometric redshift). We list the 8 candidates found in the table below:
| ZTF Name | RA (deg) | DEC (deg) | MJD | Filt | Mag | MagErr | Redshift | Note |
| ------------- | ---------- | --------- | -------- | ---- | ----- | ------ | --------------------------------------- | ---------------------------------------- |
| ZTF25aceekrn* | 180.101460 | 49.047764 | 60992.43 | g | 21.04 | 0.22 | photo-z=0.14 (LS); photo-z=0.189 (SDSS) | FAR |
| ZTF25aceekwp | 181.804049 | 55.653636 | 60992.44 | g | 21.23 | 0.20 | photo-z>0.24 (LS) | FAR |
| ZTF25aceelgz | 190.811137 | 57.328886 | 60992.47 | g | 21.15 | 0.13 | spec-z=0.476 (SDSS) | AGN-like; w1-w2=0.97 |
| ZTF25aceelbm | 169.544486 | 41.094776 | 60992.41 | g | 21.20 | 0.23 | photo-z=0.21 (LS); photo-z=0.24 (SDSS) | FAR |
| ZTF25aceemla | 185.395941 | 56.586289 | 60992.46 | r | 21.25 | 0.23 | photo-z>0.28 (LS) | FAR |
| ZTF25aceekzz | 169.076786 | 39.863435 | 60992.41 | g | 21.32 | 0.26 | photo-z=0.528 (LS) | AGN-like; ZTF pre-detections; w1-w2=1.13 |
| ZTF25aceelmh | 184.916369 | 57.167778 | 60992.47 | g | 21.61 | 0.22 | photo-z>0.41 (LS); photo-z=0.42 (SDSS) | FAR |
| ZTF25aceempu | 169.569004 | 35.985827 | 60992.49 | r | 21.60 | 0.21 | photo-z>0.23 (LS) | FAR |
*ZTF25aceekrn (AT 2025adht) was previously reported by the TROVE team (GCN 42675) with a photo-z=0.11 +/- 0.07 (nominally consistent with the LVK distance posterior). A spectrum can help resolve this discrepancy.
None of the other candidates reported here warrant additional follow-up.
All candidates have been reported to the Transient Name Server, and some are pending assignment of a TNS name.
Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Award #2407588 and a partnership including Caltech, USA; Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; University of Wisconsin at Milwaukee, USA; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; Institute of Science and Technology, Austria; National Central University, Taiwan; Operations are conducted by Caltech's Optical Observatory (COO) and Caltech/IPAC. GROWTH acknowledges the generous support of the NSF under PIRE Grant No 1545949. Alert database searches are done by AMPEL (Nordin et al. 2019) and Kowalski (Duev et al. 2019). The GROWTH India Telescope (GIT, Kumar et al., 2022) is set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. Its operations are partially supported by funding from the IIT Bombay alumni batch of 1994. The Fritz and SkyPortal projects acknowledge the generous support of The Gordon and Betty Moore Foundation.
GCN Circular 42675
N. Franz (U. Arizona), N. Vieira (Northwestern), C. D. Kilpatrick (Northwestern), D. J. Sand (U. Arizona), B. Subrayan (U. Arizona), G. Hosseinzadeh (UC San Diego), M. Shrestha (Monash U), K. D. Alexander (U. Arizona), W. Fong (Northwestern), report on behalf of the TROVE collaboration:
We analyzed candidate counterparts to the LIGO/Virgo/KAGRA (LVK) gravitational wave event S251112cm (GCN 42650) using the Multi-messenger Tool for Rapid Object Vetting and Examination (TROVE). We searched within the 95th percentile localization region for candidate optical counterparts in host galaxies at the approximate luminosity distance of S251112cm. We further crossmatch to minor planet and point source catalogs and rule out sources that do not appear photometrically similar to kilonova light curves. For additional details, see the vetting procedures described in N. Franz, et al., 2025, arXiv:2510.17104.
Below, we report all candidates that remain viable after running our vetting procedure using publicly available information on all publicly reported sources, to date, on the Transient Name Server (TNS). We include their TNS identifier, coordinates, cumulative probability at the coordinate location in the latest LVK map, most likely host redshift, most recent magnitude, and the initial reporting group. Candidates are ranked using a scoring procedure designed to identify kilonova counterparts to GW events (N. Franz, et al., 2025, arXiv:2510.17104). The reported candidates are not clearly identified as kilonovae, but we note that the progenitor system of S251112cm is poorly constrained given the exceptional attributes of the event as reported by LIGO: a probability of the system containing a neutron star < 8%, probability of containing a sub-solar mass object >99%, and a chirp mass in the range 0.1 to 0.87 solar masses.
| TNS Name | RA [HMS] | Dec [DMS] | Localization Probability Contour | Most likely Host-z | Most recent public magnitude | Discovery Survey | Comments |
|---|---|---|---|---|---|---|---|
| AT2025adht | 12:00:24.350 | +49:02:51.95 | 0.83 | 0.11 +/- 0.07 (photo-z) | g=21.4 +/- 0.2 | ZTF | |
| AT2025adgp | 01:47:46.202 | -51:49:25.52 | 0.20 | 0.06 +/- 0.02 (photo-z) | o=19.1 +/- 0.05 | BlackGEM | ATLAS pre-detection ~6 hours before S251112cm. This candidate was initially presented in GCN42663 and the ATLAS pre-detections were noted in GCN 42666. |
| AT2025adhf | 02:43:44.411 | -55:19:06.44 | 0.15 | 0.11 +/- 0.02 (photo-z) | o=19.22 +/- 0.05 | ATLAS | ATLAS pre-detections in the ~week leading up to S251112cm. |
| AT2025adhs | 04:12:56.396 | -54:11:46.41 | 0.09 | 0.04 (spec-z) | o=20.71 +/- 0.22 | BlackGEM |
We encourage additional follow up of these candidates to determine whether they remain viable counterparts to S251112cm. We note that there are 10 other transients reported to the TNS in the 95% localization region that we rule out for other reasons (e.g., excessive pre-detections, incorrect host distance as compared to S251112cm, etc.): AT2025adhj, AT2025addc, AT2025adhr, AT2025adhu, AT2025adhg, AT2025addb, AT2025adhh, AT2025adda, AT2025adhe, AT2025adgq.
GCN Circular 42674
Julius Gassert (CMU/LMU), Malte Busmann (LMU), Xander J. Hall (CMU), Brendan O’Connor (CMU), Daniel Gruen (LMU), and Antonella Palmese (CMU) report:
We observed a sample of 19 DESI galaxies, ranked by 3D position and brightness following the methodology laid out in Hall et al. (2025), in the sky localization region of gravitational wave event S251112cm (GCN 42650) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i, and J bands simultaneously. Observations started at 2025-11-12T17:43 (UT). Typical three-sigma limits for point sources are r, i ~ 21, and the field of view is 7’x7’. We do not identify any candidate GW counterpart in difference imaging with respect to Legacy Survey and PS1 data. The coordinates of the observed targets are listed below.
| R.A. | dec |
|---|---|
| 164.426910134 | 37.65453732955 |
| 165.5240393492 | 38.78722513647 |
| 167.4811243685 | 36.94655132258 |
| 173.5605908567 | 49.0431665104 |
| 182.4385674509 | 56.52359456357 |
| 182.8894005861 | 57.73745323273 |
| 186.0084874694 | 58.38519262405 |
| 196.9032263873 | 60.15719529696 |
| 197.1937364898 | 62.27166824173 |
| 250.834423606 | 70.63254712505 |
| 341.1015299287 | -0.162034769873 |
| 341.5808358893 | 3.210042314846 |
| 343.2053071078 | 1.201113639068 |
| 344.2120066199 | -8.967554297055 |
| 344.5092848207 | -3.76968999454 |
| 345.0369565289 | -12.80783236183 |
| 346.7423345683 | -9.286127524436 |
| 347.1867614296 | -12.63952485965 |
| 349.7190055484 | -10.25928200595 |
We thank Christoph Ries from the Wendelstein Observatory staff for obtaining these observations.
GCN Circular 42666
J. H. Gillanders (Oxford), S. J. Smartt, K. W. Smith (Oxford/QUB), S. Srivastav, H. Stevance, F. Stoppa, A. Cooper (Oxford), M. Nicholl, D. R. Young, C. R. Angus, M. D. Fulton, T. Moore, A. Aamer, M. McCollum, S. Sim, J. Weston, X. Sheng, D. Magill, P. Ramsden (QUB), L. Shingles (GSI/QUB), L. Rhodes (TSI/McGill), L. Denneau, J. Tonry, H. Weiland, R. Siverd (IfA, University of Hawaii), N. Erasmus, W. Koorts (South African Astronomical Observatory), A. Rest (STScI), T.-W. Chen (NCU), C. Stubbs (Harvard), J. Sommer (LMU/QUB), B. Schmidt (ANU):
We are currently observing the skymap of the LIGO/Virgo/KAGRA GW event S251112cm (LVK Collaboration, GCN 42650) with ATLAS (Tonry et al., 2018, PASP, 13, 164505; Licandro et al., 2023, arXiv:2302.07954). ATLAS is a quintuple 0.5-m optical telescope survey system (Hawaii x2, South Africa, Chile, Tenerife) employing three filters, cyan, orange and ‘clear’. In our primary NASA mission for Near-Earth Object discovery, we cover the entire visible night sky every 24 hours to a magnitude depth of m ~ 19.5, weather and Moon permitting. We will report our candidate discoveries in an upcoming GCN.
Groot et al. (GCN 42663) report on BlackGEM/MeerLICHT observations of the GW skymap of S251112cm (GCN 42650), and they present two candidate counterparts: AT2025adgp and AT2025adgq.
Here, we note that both AT2025adgp and AT2025adgq have historical detections in ATLAS, which precede the GW detection. The public ATLAS data (for these and any other transient) are accessible through the ATLAS Forced Photometry Server (Shingles et al. AstroNote #2021-7).
More specifically:
AT2025adgp was first detected on MJD 60991.136 (~0.5 days pre-GW) in the c-band with magnitude, m_c = 19.22 +/- 0.25 (AB) mag.
AT2025adgq was first detected on MJD 60988.111 (~3.5 days pre-GW) in the o-band with magnitude, m_o = 19.03 +/- 0.18 (AB) mag.
Given these pre-detections, we expect that both AT2025adgp and AT2025adgq are young, rising supernovae, unrelated to the GW signal, S251112cm. However, the exact nature of the optical counterpart to a sub-solar-mass compact object merger event is uncertain, and so we cannot rule out that these transient phenomena are related in some way. Further monitoring of these candidate events will occur with ATLAS.
The Asteroid Terrestrial-impact Last Alert System (ATLAS) project is primarily funded to search for Near-Earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from the survey area. This work was partially funded by Kepler/K2 grant J1944/80NSSC19K0112 and HST GO-15889, and STFC grants ST/T000198/1 and ST/S006109/1. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, University of Oxford, the Queen's University Belfast, the Space Telescope Science Institute, the South African Astronomical Observatory, and The Millennium Institute of Astrophysics (MAS), Chile.
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
GCN Circular 42659
H. Hiramatsu, S. Sugita, M. Serino, Y. Kawakubo, Y. Kondo (AGU)
H. Negoro, M. Nakajima, K. Takagi (Nihon U.),
N. Kawai, T. Mihara, (RIKEN),
report on behalf of the MAXI team:
We examined MAXI/GSC all-sky X-ray images (2-20 keV)
after compact binary merger candidate S251112cm at 2025-11-12 15:18:45.362 UTC (GCN #42650).
At the trigger time of S251112cm, the high-voltage of MAXI/GSC was on.
The instantaneous field of view of GSC at the GW trigger time covered 1% of the 90% credible region
of the bayestar sky map, in which we found no significant new X-ray source.
The first one-orbit (92 min) scan observation with GSC after the event covered 72%
of the 90% credible region of the bayestar skymap from 15:18:45 to 16:50:09 UTC (T0+0 to T0+5484 sec).
No significant new source was found in the region in the one-orbit scan observation.
A typical 1-sigma averaged upper limit obtained in one scan observation
is 20 mCrab at 2-20 keV.
If you require information about X-ray flux by MAXI/GSC at specific coordinates,
please contact the submitter of this circular by email.
GCN Circular 42658
K. Ackley, B. Godson, D. O'Neill, B. P. Gompertz, M. Dyer, J. Lyman, K. Ulaczyk, S. Belkin, T. Killestein, A. Kumar, M. Pursiainen, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. P. Breton, J. Casares Velásquez, L. K. Nuttall, report on behalf of the GOTO collaboration:
We carried out optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al 2024) in response to the LIGO/Virgo/KAGRA gravitational wave candidate event S251112cm (GCN 42650).
Targeted observations were performed by GOTO-South (Siding Spring, Australia) starting at 2025-11-12 16:09:51 UT, (+0.85h post trigger) and continued through to 2025-11-12 17:51:21 UT (+2.54h post trigger). A total of 39 image sets with exposures of 4x60s and 4x90s were taken across 6 unique pointings, covering 250.5 sq. degrees within the 90% localisation contour of the initial skymap. We covered approximately 14.6% of the total 2D localisation probability with an average 5-sigma depth of L~19.9 mag (AB).
Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks.
Within the initial skymap, we identify 2 optical sources within the 90% contour and 1 optical source within the 99% probability contour. We find no convincing evidence of excess flux in either GOTO25jyg/AT2025addc or GOTO25jya/AT2025adcv prior to the GW trigger time in previous GOTO observations or the ZTF observations provided by the Lasair broker (Smith et al. 2019). The ATLAS forced photometry server (Shingles et al. 2021) returns recent detections for GOTO25jyg and GOTO25jya, albeit at low significance. We encourage further analysis to confirm these pre-detections.
We note that GOTO25jya appears to be associated with a GLADE+ galaxy HyperLEDA 422311 with zphot ~ 0.01 (D_L~474 Mpc) which, if correct, would put it outside the nominal luminosity distance estimates of S251112cm.
We do not find a host galaxy underlying GOTO25jyg. There is a galaxy located 9.27 arcsec from the candidate’s position within the Legacy DR10 photometric redshift catalog with zphot ~ 0.3 (Dey et al. 2019).
GOTO25jye/AT2025adcy is located outside of the 90% probability contour of the initial skymap and is potentially associated with a GLADE+ galaxy HyperLEDA 389528 at zphot ~ 0.13 (D_L~664 Mpc). This association would make this candidate unlikely to be related to S251112cm.
| Internal name | IAU name | RA(J2000) | Dec(J2000) | Mag(AB) |
|---|---|---|---|---|
| GOTO25jyg | AT2025addc | 04:55:26.13 | -53:09:43.61 | 19.93 +/- 0.20 |
| GOTO25jya | AT2025adcv | 03:05:58.60 | -54:09:06.60 | 19.30 +/- 0.10 |
| GOTO25jye | AT2025adcy | 04:35:28.56 | -57:28:31.64 | 19.71 +/- 0.12 |
Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and not corrected for Galactic extinction. Continued observations are planned from both GOTO sites, weather permitting.
GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC).
GCN Circular 42655
S. Bala (USRA) & A. Jameson (UAH) reports on behalf of the Fermi-GBM Team:
For S251112cm (GCN 42650) and using the initial/updated bayestar/Bilby skymap, Fermi-GBM was observing 68.6% of the localization probability at event time.
There was a Fermi-GBM onboard trigger 784653403/251112637, around two mins before the event time of the LIGO/Virgo/KAGRA (LVK) detection of GW S251112cm, due to local particles (GCN 42652). An automated, blind search for short gamma-ray bursts below the onboard triggering threshold in Fermi-GBM also identified no counterpart candidates. The GBM targeted search, the most sensitive, coherent search for GRB-like signals, was run from +/-30 s around merger time, and also identified no counterpart candidates.
Part of the LVK localization region is behind the Earth for Fermi, located at an RA=4.4, Dec=25.2 with a radius of 68 degrees. We therefore set upper limits on impulsive gamma-ray emission for the GW localization region visible to Fermi at merger time. Using the representative soft, normal, and hard GRB-like templates described in arXiv:1612.02395, we set the following 3 sigma flux upper limits over 10-1000 keV, weighted by GW localization probability (in units of 10^-7 erg/s/cm^2):
Timescale Soft Normal Hard (Please put these in the appropriate units for 10^-7 erg/s/cm^2)
------------------------------------
0.128 s: 4.1 6.1 7.7
1.024 s: 2.0 2.7 3.4
8.192 s: 1.0 1.4 1.3
Assuming the median luminosity distance of 96 Mpc from the GW detection, we estimate the following intrinsic luminosity upper limits over the 1 keV-10 MeV energy range (in units of 10^47 erg/s):
Timescale Soft Normal Hard
------------------------------------
0.128s: 6.9 9.6 19.8
1.024s: 3.3 4.2 8.7
8.192s: 1.7 2.2 3.3
GCN Circular 42653
David O. Cook (Caltech/IPAC), Rick Ebert (Caltech/IPAC), George Helou (Caltech/IPAC), Joseph M. Mazzarella (Caltech/IPAC), Marion Schmitz (Caltech/IPAC), and Leo Singer (NASA/GSFC)
On behalf of the NASA/IPAC Extragalactic Database (NED) Team.
We spatially cross-matched the LVK S251112cm-3-Initial sky localization with the NED Local Volume Sample (NED-LVS; Cook et al. 2023; https://ned.ipac.caltech.edu/NED::LVS/), which is a subset of NED with a redshift or redshift-independent distance less than 1000 Mpc. We find 7731 galaxies within the 90% containment volume, and we list here the top 20 galaxies sorted by the joint probability of the 3D localization and the WISE W1 luminosity (an observable proxy for stellar mass). For the full or top 20 list of galaxies in the 90% volume go either to the NED Gravitational Wave Followup service at https://ned.ipac.caltech.edu/uri/NED::GWF/ or click on the following links:
Full List Download: https://ned.ipac.caltech.edu/uri/NED::GWFglist/fits/S251112cm/3
Top 20 List Download: https://ned.ipac.caltech.edu/uri/NED::GWFglist/fits/S251112cm/3/20
The NED-GWF service provides downloadable galaxy lists and visualizations for candidate host galaxies. For each GW alert, these products are automatically generated and made available within minutes to expedite efficient electromagnetic follow-up observations. The NED top 20 list is sorted by the joint probability of the 3D localization and the WISE W1 luminosity, but users can sort on additional pre-computed prioritization metrics (star formation rate, P_3D * P_SFR; and specific star formation rate, P_3D * P_sSFR; etc.) which are available via downloading the entire galaxy list inside the event's probability volume.
| objname | ra | dec | objtype | DistMpc | DistMpc_unc | m_NUV | m_NUV_unc | m_Ks | m_Ks_unc | m_W1 | m_W1_unc | P_3D | P_3D_LumW1 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| NGC 2960 | 145.15161 | 3.57703 | G | 76.97 | 7.94 | 17.522 | 0.003 | 9.783 | 0.038 | 9.672 | 0.002 | 1.71e-05 | 1.08e-08 |
| IC 1471 | 347.18676 | -12.63948 | G | 83.00 | 17.58 | 17.246 | 0.027 | 10.334 | 0.035 | 10.290 | 0.006 | 1.79e-05 | 7.44e-09 |
| NGC 7396 | 343.09426 | 1.09241 | G | 81.16 | 8.50 | 17.854 | 0.004 | 8.699 | 0.022 | 8.557 | 0.012 | 3.66e-06 | 7.25e-09 |
| UGC 05226 | 146.51479 | 4.40348 | G | 66.86 | 15.78 | 18.763 | 0.092 | 10.211 | 0.041 | 10.083 | 0.089 | 2.17e-05 | 7.08e-09 |
| IC 0564 | 146.58792 | 3.07130 | G | 75.75 | 2.62 | null | null | 10.033 | 0.035 | 10.010 | 0.006 | 1.51e-05 | 6.79e-09 |
| NGC 3070 | 149.52893 | 10.35980 | G | 60.25 | 5.89 | 18.225 | 0.068 | 9.260 | 0.030 | 9.503 | 0.006 | 1.45e-05 | 6.56e-09 |
| IC 1464B | 345.79587 | -8.98909 | G | 105.88 | 0.59 | null | null | 10.015 | 0.036 | 9.741 | 0.006 | 5.69e-06 | 6.38e-09 |
| WISEA J100012.04+093856.0 | 150.05020 | 9.64890 | G | 78.82 | 0.30 | null | null | 11.073 | 0.096 | 10.233 | 0.006 | 1.53e-05 | 6.05e-09 |
| UGCA 150 | 137.70611 | -8.89069 | G | 28.38 | 0.82 | null | null | 7.704 | 0.006 | 7.044 | 0.041 | 5.28e-06 | 5.11e-09 |
| IC 1633 | 17.48145 | -45.93116 | G | 96.06 | 3.43 | null | null | 8.396 | 0.025 | 8.999 | 0.006 | 2.80e-06 | 5.10e-09 |
| NGC 3540 | 167.31704 | 36.02108 | G | 93.24 | 0.04 | 19.626 | 0.150 | 10.168 | 0.041 | 10.319 | 0.006 | 9.87e-06 | 5.03e-09 |
| NGC 2987 | 146.42281 | 4.94189 | G | 54.46 | 0.58 | 17.338 | 0.002 | 10.146 | 0.048 | 9.912 | 0.006 | 1.97e-05 | 4.99e-09 |
| NGC 7646 | 351.02906 | -11.86050 | G | 79.59 | 2.73 | 16.328 | 0.004 | 10.358 | 0.037 | 8.371 | 0.005 | 2.21e-06 | 4.94e-09 |
| MCG -01-24-010 | 140.09147 | -7.88074 | G | 53.94 | 2.54 | 15.885 | 0.007 | 10.054 | 0.032 | 9.821 | 0.030 | 1.78e-05 | 4.81e-09 |
| ESO 197- G 021 | 31.13585 | -52.17213 | G | 87.54 | 0.39 | null | null | 9.099 | 0.026 | 9.375 | 0.006 | 4.26e-06 | 4.56e-09 |
| NGC 4187 | 183.37201 | 50.74150 | G | 120.62 | 5.52 | 18.691 | 0.027 | 9.772 | 0.027 | 9.930 | 0.006 | 3.73e-06 | 4.56e-09 |
| UGC 05267 | 147.47044 | 9.09562 | G | 80.08 | 3.03 | null | null | 10.147 | 0.042 | 10.208 | 0.006 | 1.08e-05 | 4.52e-09 |
| NGC 7364 | 341.10153 | -0.16213 | G | 76.48 | 8.25 | 16.366 | 0.001 | 9.478 | 0.028 | 9.218 | 0.003 | 4.69e-06 | 4.46e-09 |
| NGC 0010 | 2.14394 | -33.85835 | G | 87.84 | 3.70 | null | null | 9.205 | 0.042 | 9.975 | 0.006 | 7.18e-06 | 4.45e-09 |
| UGC 05855 | 161.15400 | 26.18153 | G | 91.46 | 2.06 | 17.681 | 0.037 | 10.212 | 0.028 | 10.184 | 0.006 | 7.99e-06 | 4.45e-09 |
Table 1: Top 20 galaxies in NED-LVS that fall in the 90% probability volume for S251112cm sorted by the joint probability of 3D position and WISE W1 luminosity (P_3D * P_LumW1). Galaxy is the NED preferred name. RA and Dec are the Equatorial coordinates in degrees (J2000). Objtype is the object type of the galaxy candidate. Distance is the distance to the galaxy in Mpc. m_NUV and mErr_NUV are the apparent magnitude and error from GALEX. m_Ks and mErr_Ks are the apparent magnitude and error from 2MASS. m_W1 and mErr_W1 are the apparent magnitude and error from AllWISE. P_3D is the probability that the galaxy is in the volume given the distance of GW event. P_3D_LumW1 is the joint probability within the volume weighted by the WISE1 luminosity of the galaxy (P_3D * P_LumW1).
GCN Circular 42650
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We identified the compact binary merger candidate S251112cm during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-11-12 15:18:45.362 UTC (GPS time: 1446995943.362). The candidate was found by the MBTA SSM [1] analysis pipeline.
S251112cm is an event of interest because its false alarm rate, as estimated by the online analysis, is 5.1e-09 Hz, or about one in 6 years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S251112cm
The analysis which found this candidate used a template bank including sub-solar-mass components. The usual classification probabilities for BNS, NSBH, or BBH binaries versus Terrestrial noise are not calculated for this candidate. The probability of matter remaining outside the final compact object (HasRemnant) [2] is not estimated either.
Assuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass between 1 and 3 solar masses (HasNS) is 8%. [2] The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%. The probability that the lighter compact object is below 1 solar mass (HasSSM) is >99%.
The source chirp mass falls with highest probability in the bin (0.1, 0.87) solar masses, assuming the candidate is astrophysical in origin.
Two sky maps are available at this time and can be retrieved from the GraceDB event page:
* bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [3], distributed via GCN and SCiMMA notices about 57 seconds after the candidate event time.
* bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [3], distributed via GCN and SCiMMA notices about 5 minutes after the candidate event time.
The preferred sky map at this time is bayestar.multiorder.fits,1. For the bayestar.multiorder.fits,1 sky map, the 90% credible region is 1220 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 96 +/- 29 Mpc (a posteriori mean +/- standard deviation).
For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/.
[1] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234
[2] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe
[3] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013