TITLE: GCN CIRCULAR NUMBER: 25695 SUBJECT: LIGO/Virgo S190910d: Identification of a GW compact binary merger candidate DATE: 19/09/10 02:29:05 GMT FROM: Francesca Badaracco at GSSI, Ligo/VIRGO The LIGO Scientific Collaboration and the Virgo Collaboration report: We identified the compact binary merger candidate S190910d during real-time processing of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) at 2019-09-10 01:26:19.243 UTC (GPS time: 1252113997.243). The candidate was found by the SPIIR [1] and MBTAOnline [2] analysis pipelines. S190910d is an event of interest because its false alarm rate, as estimated by the online analysis, is 3.7e-09 Hz, or about one in 8 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S190910d The classification of the GW signal, in order of descending probability, is NSBH (98%), Terrestrial (2%), BNS (<1%), BBH (<1%), or MassGap (<1%). Assuming the candidate is astrophysical in origin, there is strong evidence for the lighter compact object having a mass < 3 solar masses (HasNS: >99%). 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 [3], distributed via GCN notice about 6 minutes after the candidate For the bayestar.fits.gz sky map, the 90% credible region is 3829 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 606 +/- 197 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] Adams et al. CQG 33, 175012 (2016) [3] Singer & Price PRD 93, 024013 (2016)