TITLE: GCN CIRCULAR NUMBER: 24237 SUBJECT: LIGO/Virgo S190426c: Identification of a GW compact binary merger candidate DATE: 19/04/26 16:45:04 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 S190426c during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2019-04-26 15:21:55.337 UTC (GPS time: 1240327333.337). The candidate was found by the GstLAL [1], MBTAOnline [2], PyCBC Live [3], and SPIIR [4] analysis pipelines. S190426c is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.9e-08 Hz, or about one in 1 year, 7 months. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S190426c The classification of the GW signal, in order of descending probability, is BNS (49%), MassGap (24%), Terrestrial (14%), NSBH (13%), or BBH (<1%). Assuming the candidate is astrophysical in origin, there is strong evidence for the lighter compact object having a mass < 3 solar masses (HasNS: >99%). Using the masses and spins inferred from the signal, there is strong evidence for matter outside the final compact object (HasRemnant: >99%). Two skymaps are available at this time and can be retrieved from the GraceDB event page: * bayestar.fits.gz, the preliminary sky localization generated by BAYESTAR [5], distributed via GCN notice about 25 minutes after the candidate, * bayestar1.fits.gz, an updated localization distributed via GCN notice about an hour after the candidate. This is the preferred skymap at this time. For the bayestar1.fits.gz skymap, the 90% credible region is 1262 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 375 +/- 108 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] Adams et al. CQG 33, 175012 (2016) [3] Nitz et al. PRD 98, 024050 (2018) [4] Qi Chu, PhD Thesis, The University of Western Australia (2017) [5] Singer & Price PRD 93, 024013 (2016) [GCN OPS NOTE(30apr19): Per author's request, the double spacing was removed.]