TITLE: GCN CIRCULAR NUMBER: 26350 SUBJECT: LIGO/Virgo S191205ah: Identification of a GW compact binary merger candidate DATE: 19/12/05 22:35:27 GMT FROM: Deep Chatterjee at University of Wisconsin, Milwaukee The LIGO Scientific Collaboration and the Virgo Collaboration report: We identified the compact binary merger candidate S191205ah during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2019-12-05 21:52:08.569 UTC (GPS time: 1259617946.569). The candidate was found by the GstLAL [1] analysis pipeline. S191205ah is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.2e-08 Hz, or about one in 2 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S191205ah The classification of the GW signal, in order of descending probability, is NSBH (93%), Terrestrial (7%), BNS (<1%), BBH (<1%), or MassGap (<1%). Assuming the candidate is astrophysical in origin, the probability that the lighter compact object has a mass < 3 solar masses (HasNS) is >99%. Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. Two sky maps are available at this time and can be retrieved from the GraceDB event page: * bayestar.fits.gz,0, an initial localization generated by BAYESTAR [2], distributed via GCN notice about 2 minutes after the candidate event time. * bayestar.fits.gz,1, an initial localization generated by BAYESTAR [2], distributed via GCN notice about 8 minutes after the candidate event time. The preferred sky map at this time is bayestar.fits.gz,1. For the bayestar.fits.gz,1 sky map, the 90% credible region is 6378 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 385 +/- 164 Mpc (a posteriori mean +/- standard deviation). For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo Public Alerts User Guide . [1] Messick et al. PRD 95, 042001 (2017) [2] Singer & Price PRD 93, 024013 (2016)