TITLE: GCN CIRCULAR NUMBER: 26454 SUBJECT: LIGO/Virgo S191216ap: Identification of a GW compact binary merger candidate DATE: 19/12/16 22:03:55 GMT FROM: Brandon Piotrzkowski at U of Wisconsin-Milwaukee The LIGO Scientific Collaboration and the Virgo Collaboration report: We identified the compact binary merger candidate S191216ap during real-time processing of data from LIGO Hanford Observatory (H1) and Virgo Observatory (V1) at 2019-12-16 21:33:38.473 UTC (GPS time: 1260567236.473). The candidate was found by the GstLAL [1], MBTAOnline [2], and PyCBC Live [3] analysis pipelines. S191216ap is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.1e-23 Hz, or about one in 1e15 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S191216ap The classification of the GW signal, in order of descending probability, is MassGap (>99%), Terrestrial (<1%), BNS (<1%), BBH (<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 19%. Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. One sky map is available at this time and can be retrieved from the GraceDB event page: * bayestar.fits.gz,0, an initial localization generated by BAYESTAR [4], distributed via GCN notice about 16 minutes after the candidate event time. For the bayestar.fits.gz,0 sky map, the 90% credible region is 300 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 324 +/- 78 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] Adams et al. CQG 33, 175012 (2016) [3] Nitz et al. PRD 98, 024050 (2018) [4] Singer & Price PRD 93, 024013 (2016)