TITLE: GCN CIRCULAR NUMBER: 26303 SUBJECT: LIGO/Virgo S191129u: Identification of a GW compact binary merger candidate DATE: 19/11/29 14:38:28 GMT FROM: Leo Singer at GSFC The LIGO Scientific Collaboration and the Virgo Collaboration report: We identified the compact binary merger candidate S191129u during real-time processing of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) at 2019-11-29 13:40:29.197 UTC (GPS time: 1259070047.197). The candidate was found by the GstLAL [1], MBTAOnline [2], SPIIR [3], and PyCBC Live [4] analysis pipelines. S191129u is an event of interest because its false alarm rate, as estimated by the online analysis, is 2.7e-35 Hz, or about one in 1e27 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S191129u 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%. 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 [5], distributed via GCN notice about 42 minutes after the candidate event time. For the bayestar.fits.gz,0 sky map, the 90% credible region is 1011 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 763 +/- 200 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] Qi Chu, PhD Thesis, The University of Western Australia (2017) [4] Nitz et al. PRD 98, 024050 (2018) [5] Singer & Price PRD 93, 024013 (2016)