LIGO/Virgo/KAGRA S251014cn
GCN Circular 42306
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We have conducted further analysis of the LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) data around the time of the compact binary merger (CBC) candidate S251014cn (GCN Circular 42255. Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page:
https://gracedb.ligo.org/superevents/S251014cn
For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 172 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 607 +/- 164 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] 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
GCN Circular 42260
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 S251014cn-3-Initial sky localization with the NED Local Volume Sample (NED-LVS; Cook et al. 2023), which is a subset of NED with a redshift or redshift-independent distance less than 1000 Mpc. We find 10691 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/S251014cn/3
Top 20 List Download: https://ned.ipac.caltech.edu/uri/NED::GWFglist/fits/S251014cn/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 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| WISEA J204706.11-222948.1 | 311.77550 | -22.49672 | G | 727.73 | 4.31 | null | null | 14.677 | 0.171 | 9.127 | 0.006 | 1.25e-07 | 1.19e-09 |
| WISEA J210442.39-250658.2 | 316.17666 | -25.11619 | G | 632.49 | 0.65 | null | null | 12.233 | 0.093 | 9.702 | 0.006 | 1.67e-07 | 7.14e-10 |
| [HB89] 2155-304 | 329.71694 | -30.22559 | QSO | 546.26 | 0.43 | 13.401 | 0.001 | 10.101 | 0.013 | 9.233 | 0.006 | 8.29e-08 | 4.03e-10 |
| WISEA J203200.13-212013.9 | 308.00055 | -21.33721 | G | 686.01 | null | null | null | 13.471 | 0.172 | 11.048 | 0.007 | 2.64e-07 | 3.82e-10 |
| WISEA J195711.85-155450.4 | 299.29942 | -15.91401 | G | 464.26 | null | null | null | 13.148 | 0.182 | 9.223 | 0.006 | 9.41e-08 | 3.41e-10 |
| WISEA J210053.37-260056.2 | 315.22239 | -26.01562 | G | 523.86 | null | 20.640 | 0.211 | 13.660 | 0.182 | 10.671 | 0.006 | 2.12e-07 | 2.55e-10 |
| WISEA J202657.64-194510.3 | 306.74020 | -19.75287 | G | 536.72 | 0.65 | null | null | 12.502 | 0.088 | 10.962 | 0.006 | 2.42e-07 | 2.33e-10 |
| WISEA J233456.39-265518.6 | 353.73499 | -26.92184 | G | 280.74 | 0.65 | null | null | 11.229 | 0.056 | 8.467 | 0.005 | 8.37e-08 | 2.18e-10 |
| WISEA J195521.91-151547.2 | 298.84130 | -15.26312 | G | 485.70 | null | null | null | 13.338 | 0.163 | 10.223 | 0.007 | 1.19e-07 | 1.91e-10 |
| WISEA J211913.50-272622.9 | 319.80626 | -27.43970 | G | 533.96 | null | 21.251 | 0.278 | 13.385 | 0.135 | 11.169 | 0.007 | 2.33e-07 | 1.84e-10 |
| WISEA J201311.18-190314.5 | 303.29661 | -19.05404 | G | 572.05 | null | null | null | 13.451 | 0.145 | 11.150 | 0.007 | 1.75e-07 | 1.62e-10 |
| WISEA J202635.83-202306.5 | 306.64930 | -20.38515 | G | 735.83 | 0.65 | null | null | 12.556 | 0.102 | 11.879 | 0.008 | 2.08e-07 | 1.62e-10 |
| WISEA J202559.97-203159.0 | 306.49991 | -20.53307 | G | 732.69 | 0.65 | null | null | 12.200 | 0.114 | 11.897 | 0.012 | 2.03e-07 | 1.54e-10 |
| WISEA J214110.24-264550.3 | 325.29269 | -26.76397 | QSO | 608.68 | null | 16.698 | 0.017 | 11.077 | 0.012 | 9.482 | 0.006 | 3.03e-08 | 1.46e-10 |
| WISEA J204622.40-223419.0 | 311.59335 | -22.57195 | G | 685.98 | 4.31 | null | null | 15.453 | 0.346 | 11.646 | 0.007 | 1.74e-07 | 1.46e-10 |
| WISEA J200050.95-154454.3 | 300.21230 | -15.74842 | G | 688.87 | null | null | null | 13.684 | 0.252 | 11.792 | 0.008 | 1.90e-07 | 1.41e-10 |
| WISEA J193249.64-101803.3 | 293.20684 | -10.30092 | G | 410.47 | 0.65 | null | null | 12.248 | 0.139 | 9.373 | 0.006 | 5.53e-08 | 1.39e-10 |
| WISEA J210524.13-254016.4 | 316.35056 | -25.67124 | G | 492.45 | null | null | null | 13.568 | 0.159 | 11.429 | 0.007 | 2.62e-07 | 1.38e-10 |
| WISEA J202206.73-184638.7 | 305.52808 | -18.77742 | G | 497.59 | 0.65 | 19.597 | 0.097 | 12.293 | 0.055 | 11.011 | 0.007 | 1.75e-07 | 1.38e-10 |
| WISEA J201415.46-192535.3 | 303.56468 | -19.42654 | G | 602.46 | null | null | null | 13.720 | 0.165 | 11.210 | 0.007 | 1.39e-07 | 1.35e-10 |
Table 1: Top 20 galaxies in NED-LVS that fall in the 90% probability volume for S251014cn 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 42255
The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report:
We identified the compact binary merger candidate S251014cn during real-time processing of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) at 2025-10-14 11:33:23.373 UTC (GPS time: 1444476821.373). The candidate was found by the Aframe [1], cWB [2], cWB BBH [3], GstLAL [4], MBTA [5], MLy [6], PyCBC Live [7], and SPIIR [8] analysis pipelines.
S251014cn is an event of interest because its false alarm rate, as estimated by the online analysis, is 3.2e-10 Hz, or about one in 1e2 years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S251014cn
The classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), BNS (<1%), or NSBH (<1%).
Assuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [9] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [9] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%.
The source chirp mass falls with highest probability in the bin (11.0, 22.0) 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 [10], distributed via GCN and SCiMMA notices about 24 seconds after the candidate event time.
* bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [10], 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 233 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 610 +/- 172 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] Marx et al. PRD 111, 042010 (2025) doi:10.1103/PhysRevD.111.042010
[2] Klimenko et al. PRD 93, 042004 (2016) doi:10.1103/PhysRevD.93.042004
[3] T. Mishra et al. PRD 105, 083018 (2022) doi:10.1103/PhysRevD.105.083018
[4] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. PRD 109, 042008 (2024) doi:10.1103/PhysRevD.109.042008
[5] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234
[6] Skliris et al. PRD 110, 104034 (2024) doi:10.1103/PhysRevD.110.104034
[7] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a
[8] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023
[9] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe
[10] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013