TITLE: GCN CIRCULAR NUMBER: 25164 SUBJECT: LIGO/Virgo S190727h: Identification of a GW compact binary merger candidate DATE: 19/07/27 07:31:42 GMT FROM: Shaon Ghosh at UWM The LIGO Scientific Collaboration and the Virgo Collaboration report: We identified the compact binary merger candidate S190727h during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2019-07-27 06:03:33.986 UTC (GPS time: 1248242631.986). The candidate was found by the GstLAL [1], CWB [2], PyCBC Live [3], MBTAOnline [4], and SPIIR [5] analysis pipelines. S190727h is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.4e-10 Hz, or about one in 1e2 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S190727h The classification of the GW signal, in order of descending probability, is BBH (92%), Terrestrial (5%), MassGap (3%), NSBH (<1%), or BNS (<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 8 minutes after the candidate For the bayestar.fits.gz sky map, the 90% credible region is 841 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2022 +/- 516 Mpc (a posteriori mean +/- standard deviation). Note that the preliminary GCN notice incorrectly reported the classification as 99% Terrestrial, and the incorrect skymap was associated with the event. These have now been corrected. 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)