TITLE: GCN CIRCULAR NUMBER: 26202 SUBJECT: LIGO/Virgo S191109d: Identification of a GW compact binary merger candidate DATE: 19/11/09 01:50:16 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 S191109d during real-time processing of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) at 2019-11-09 01:07:17.221 UTC (GPS time: 1257296855.221). The candidate was found by the SPIIR [1], CWB [2], GstLAL [3], MBTAOnline [4], and PyCBC Live [5] analysis pipelines. S191109d is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.5e-13 Hz, or about one in 2e5 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S191109d The classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), BNS (<1%), NSBH (<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 <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 [6], distributed via GCN notice about 9 minutes after the candidate event time. For the bayestar.fits.gz,0 sky map, the 90% credible region is 1487 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1810 +/- 604 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] Qi Chu, PhD Thesis, The University of Western Australia (2017) [2] Klimenko et al. PRD 93, 042004 (2016) [3] Messick et al. PRD 95, 042001 (2017) [4] Adams et al. CQG 33, 175012 (2016) [5] Nitz et al. PRD 98, 024050 (2018) [6] Singer & Price PRD 93, 024013 (2016)