TITLE: GCN CIRCULAR NUMBER: 26543 SUBJECT: LIGO/Virgo S191222n: Identification of a GW compact binary merger candidate DATE: 19/12/22 04:14:57 GMT FROM: Sarah Antier at APC The LIGO Scientific Collaboration and the Virgo Collaboration report: We identified the compact binary merger candidate S191222n during real-time processing of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) at 2019-12-22 03:35:37.119 UTC (GPS time: 1261020955.119). The candidate was found by the GstLAL [1], SPIIR [2], and CWB [3] analysis pipelines. S191222n is an event of interest because its false alarm rate, as estimated by the online analysis, is 6.5e-12 Hz, or about one in 5e3 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S191222n 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, 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 [4], distributed via GCN notice about 3 minutes after the candidate event time.  * bayestar.fits.gz,1, an initial localization generated by BAYESTAR [4], distributed via GCN notice about 9 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 2324 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 868 +/- 265 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] Singer & Price PRD 93, 024013 (2016)