TITLE: GCN CIRCULAR NUMBER: 25753 SUBJECT: LIGO/Virgo S190915ak: Identification of a GW compact binary merger candidate DATE: 19/09/16 00:27:49 GMT FROM: Alan Weinstein at Caltech/LIGO The LIGO Scientific Collaboration and the Virgo Collaboration report: We identified the compact binary merger candidate S190915ak during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2019-09-15 23:57:02.691 UTC (GPS time: 1252627040.691). The candidate was found by the GstLAL [1], SPIIR [2], CWB [3], and MBTAOnline [4] analysis pipelines. S190915ak is an event of interest because its false alarm rate, as estimated by the online analysis, is 9.7e-10 Hz, or about one in 32 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S190915ak The classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), BNS (<1%), MassGap (<1%), or NSBH (<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 [5], distributed via GCN notice about 6 minutes after the candidate trigger time. For the bayestar.fits.gz sky map, the 90% credible region is 528 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1557 +/- 381 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] Messick et al. PRD 95, 042001 (2017) [2] Qi Chu, PhD Thesis, The University of Western Australia (2017) [3] Klimenko et al. PRD 93, 042004 (2016) [4] Adams et al. CQG 33, 175012 (2016) [5] Singer & Price PRD 93, 024013 (2016) [GCN OPS NOTE(15sep19): Per author's request, "trigger time." was added to the end of the first sentence in the fifth paragraph.]