TITLE: GCN CIRCULAR NUMBER: 24503 SUBJECT: LIGO/Virgo S190512at: Identification of a GW compact binary merger candidate DATE: 19/05/12 19:05:01 GMT FROM: Deep Chatterjee at University of Wisconsin, Milwaukee The LIGO Scientific Collaboration and the Virgo Collaboration report: We identified the compact binary merger candidate S190512at during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2019-05-12 18:07:14.422 UTC (GPS time: 1241719652.422). The candidate was found by the PyCBC Live [1], CWB [2], GstLAL [3], MBTAOnline [4], and spiir [5] analysis pipelines. S190512at is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.9e-09 Hz, or about one in 16 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S190512at The classification of the GW signal, in order of descending probability, is BBH (99%), Terrestrial (1%), BNS (<1%), NSBH (<1%), or MassGap (<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 skymap 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 53 minutes after the candidate. For the bayestar.fits.gz skymap, the 90% credible region is 399 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1331 +/- 341 Mpc (a posteriori mean +/- standard deviation). No Preliminary Notice was sent for this event due to a technical problem. 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] Messick et al. PRD 95, 042001 (2017) [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)