TITLE: GCN CIRCULAR NUMBER: 27130 SUBJECT: LIGO/Virgo S200219ac: Identification of a GW compact binary merger candidate DATE: 20/02/19 12:53:35 GMT FROM: Sarah Antier at APC The LIGO Scientific Collaboration and the Virgo Collaboration report: We identified the compact binary merger candidate S200219ac during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2020-02-19 09:44:15.195 UTC (GPS time: 1266140673.195). The candidate was found by the PyCBC Live [1], CWB [2], MBTAOnline [3], SPIIR [4], and GstLAL [5] analysis pipelines. The delay in issuing the alert was due to a software issue in the online system. S200219ac is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.3e-08 Hz, or about one in 2 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S200219ac The classification of the GW signal, in order of descending probability, is BBH (96%), Terrestrial (4%), 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, an updated localization generated by BAYESTAR [6], distributed via GCN notice about 2 hours after the candidate. The preferred sky map at this time is bayestar.fits.gz. For the bayestar.fits.gz sky map, the 90% credible region is 1251 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1510 +/- 405 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] Nitz et al. PRD 98, 024050 (2018)  [2] Klimenko et al. PRD 93, 042004 (2016)  [3] Adams et al. CQG 33, 175012 (2016)  [4] Qi Chu, PhD Thesis, The University of Western Australia (2017)  [5] Messick et al. PRD 95, 042001 (2017)  [6] Singer & Price PRD 93, 024013 (2016)