TITLE: GCN CIRCULAR NUMBER: 25829 SUBJECT: LIGO/Virgo S190924h: Identification of a GW compact binary merger candidate DATE: 19/09/24 03:14:19 GMT FROM: Geoffrey Mo at LIGO The LIGO Scientific Collaboration and the Virgo Collaboration report: We identified the compact binary merger candidate S190924h during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2019-09-24 02:18:46.847 UTC (GPS time: 1253326744.847). The candidate was found by the GstLAL [1], PyCBC Live [2], MBTAOnline [3], and SPIIR [4] analysis pipelines. S190924h is an event of interest because its false alarm rate, as estimated by the online analysis, is 8.9e-19 Hz, or about one in 1e11 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S190924h The classification of the GW signal, in order of descending probability, is MassGap (>99%), Terrestrial (<1%), BNS (<1%), BBH (<1%), or NSBH (<1%). Assuming the candidate is astrophysical in origin, there is indeterminate evidence for the lighter compact object having a mass < 3 solar masses (HasNS: 30%). 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,0, an updated localization generated by BAYESTAR [5], distributed via GCN notice about 6 minutes after the candidate For the bayestar.fits.gz,0 sky map, the 90% credible region is 515 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 514 +/- 132 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] Nitz et al. PRD 98, 024050 (2018) [3] Adams et al. CQG 33, 175012 (2016) [4] Qi Chu, PhD Thesis, The University of Western Australia (2017) [5] Singer & Price PRD 93, 024013 (2016)