TITLE: GCN CIRCULAR NUMBER: 42650 SUBJECT: LIGO/Virgo/KAGRA S251112cm: Identification of a GW compact binary merger candidate DATE: 25/11/12 15:55:25 GMT FROM: Alicia Calafat <alicia.calafat@ligo.org> 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 View this GCN Circular online at https://gcn.nasa.gov/circulars/42650. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...