TITLE: GCN CIRCULAR NUMBER: 27193 SUBJECT: LIGO/Virgo S200225q: Identification of a GW compact binary merger candidate The LIGO Scientific Collaboration and the Virgo Collaboration DATE: 20/02/25 06:38:12 GMT FROM: Vinaya Valsan at U. of Wisconsin Milwaukee We identified the compact binary merger candidate S200225q during real-time processing of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) at 2020-02-25 06:04:21.397 UTC (GPS time: 1266645879.397). The candidate was found by the PyCBC Live [1], CWB [2], MBTAOnline [3], GstLAL [4], and SPIIR [5] analysis pipelines. S200225q is an event of interest because its false alarm rate, as estimated by the online analysis, is 9.2e-09 Hz, or about one in 3 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S200225q 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%. Two sky maps are 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 3 minutes after the candidate event time. * bayestar.fits.gz,1, an initial localization generated by BAYESTAR [6], distributed via GCN notice about 11 minutes after the candidate event time. The preferred sky map at this time is bayestar.fits.gz,1. For the bayestar.fits.gz,1 sky map, the 90% credible region is 668 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1234 +/- 341 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] Messick et al. PRD 95, 042001 (2017) [5] Qi Chu, PhD Thesis, The University of Western Australia (2017) [6] Singer & Price PRD 93, 024013 (2016)