TITLE: GCN CIRCULAR NUMBER: 39175 SUBJECT: LIGO/Virgo/KAGRA S250206dm: Identification of a GW compact binary merger candidate DATE: 25/02/06 22:00:22 GMT FROM: youru.lee@g.ncu.edu.tw The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250206dm during real-time processing of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) at 2025-02-06 21:25:30.439 UTC (GPS time: 1422912348.439). The candidate was found by the GstLAL [1], MBTA [2], and PyCBC Live [3] analysis pipelines. S250206dm is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.3e-09 Hz, or about one in 25 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250206dm The classification of the GW signal, in order of descending probability, is NSBH (55%), BNS (37%), Terrestrial (8%), or BBH (<1%). Assuming the candidate is astrophysical in origin, the probability that the lighter compact object is consistent with a neutron star mass (HasNS) is >99%. [4] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is 30%. [4] Both HasNS and HasRemnant consider the support of several neutron star equations of state. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is 62%. 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 [5], distributed via GCN notice about 31 seconds after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [5], distributed via GCN notice 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 1544 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 409 +/- 139 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] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. (2023) arXiv:2305.05625 [2] Aubin et al. CQG 38, 095004 (2021) doi:10.1088/1361-6382/abe913 [3] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a [4] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [5] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/39175. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...