TITLE: GCN CIRCULAR NUMBER: 26926 SUBJECT: LIGO/Virgo S200129m: Identification of a GW compact binary merger candidate DATE: 20/01/29 08:05:31 GMT FROM: Brandon Piotrzkowski at U of Wisconsin-Milwaukee The LIGO Scientific Collaboration and the Virgo Collaboration report: We identified the compact binary merger candidate S200129m during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2020-01-29 06:54:58.435 UTC (GPS time: 1264316116.435). The candidate was found by the GstLAL [1], CWB [2], PyCBC Live [3], MBTAOnline [4], and SPIIR [5] analysis pipelines. Some scattering noise could be seen around the time of the event in Virgo data; follow-up studies are on-going. We will update the localization if warranted by offline analysis. S200129m is an event of interest because its false alarm rate, as estimated by the online analysis, is 6.7e-32 Hz, or about one in 1e23 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S200129m 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 [6], distributed via GCN notice about 4 minutes after the candidate event time. * bayestar.fits.gz,1, an initial localization generated by BAYESTAR [6], distributed via GCN notice about 13 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 53 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 908 +/- 202 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] Klimenko et al. PRD 93, 042004 (2016) [3] Nitz et al. PRD 98, 024050 (2018) [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)