TITLE: GCN CIRCULAR NUMBER: 26441 SUBJECT: LIGO/Virgo S191215w: Identification of a GW compact binary merger candidate DATE: 19/12/15 23:04:15 GMT FROM: Nelson Christensen at Obs.de la Cote dAzur,Nice The LIGO Scientific Collaboration and the Virgo Collaboration report: We identified the compact binary merger candidate S191215w during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2019-12-15 22:30:52.333 UTC (GPS time: 1260484270.333). The candidate was found by the GstLAL [1], CWB [2], MBTAOnline [3], and PyCBC Live [4] analysis pipelines. S191215w is an event of interest because its false alarm rate, as estimated by the online analysis, is 1e-09 Hz, or about one in 31 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S191215w The classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), BNS (<1%), MassGap (<1%), or NSBH (<1%). Assuming the candidate is astrophysical in origin, the probability that the lighter compact object has a mass < 3 solar masses (HasNS) is <1%. 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 [5], distributed via GCN notice about 7 minutes after the candidate event time. * bayestar.fits.gz,1, an initial localization generated by BAYESTAR [5], distributed via GCN notice about 15 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 923 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2216 +/- 590 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] Klimenko et al. PRD 93, 042004 (2016) [3] Adams et al. CQG 33, 175012 (2016) [4] Nitz et al. PRD 98, 024050 (2018) [5] Singer & Price PRD 93, 024013 (2016)