TITLE: GCN CIRCULAR NUMBER: 25497 SUBJECT: LIGO/Virgo S190828j: Identification of a GW compact binary merger candidate DATE: 19/08/28 07:17:40 GMT FROM: Olivier Minazzoli at LIGO Virgo Collaboration The LIGO Scientific Collaboration and the Virgo Collaboration report: We identified the compact binary merger candidate S190828j during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2019-08-28 06:34:05.756 UTC (GPS time: 1251009263.756). The candidate was found by the GstLAL [1], CWB [2], PyCBC Live [3], MBTAOnline [4], and SPIIR [5] analysis pipelines. S190828j is an event of interest because its false alarm rate, as estimated by the online analysis, is 8.5e-22 Hz, or about one in 1e14 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S190828j 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, there is strong evidence against the lighter compact object having a mass < 3 solar masses (HasNS: <1%). Using the masses and spins inferred from the signal, there is strong evidence against matter outside the final compact object (HasRemnant: <1%). One sky map is available at this time and can be retrieved from the GraceDB event page: * bayestar.fits.gz, an updated localization generated by BAYESTAR [6], distributed via GCN notice about 16 minutes after the candidate For the bayestar.fits.gz sky map, the 90% credible region is 603 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2276 +/- 538 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] Nitz et al. PRD 98, 024050 (2018) [4] Adams et al. CQG 33, 175012 (2016) [5] Qi Chu, PhD Thesis, The University of Western Australia (2017) [6] Singer & Price PRD 93, 024013 (2016)