TITLE: GCN CIRCULAR NUMBER: 25876 SUBJECT: LIGO/Virgo S190930t: Identification of a GW compact binary merger candidate DATE: 19/09/30 15:29:21 GMT FROM: Olivier Minazzoli at LIGO Virgo Collaboration The LIGO Scientific Collaboration and the Virgo Collaboration report: We identified the compact binary merger candidate S190930t during real-time processing of data from LIGO Livingston Observatory (L1) at 2019-09-30 14:34:07.685 UTC (GPS time: 1253889265.685). The candidate was found by the GstLAL [1] analysis pipeline. S190930t is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.5e-08 Hz, or about one in 2 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S190930t The classification of the GW signal, in order of descending probability, is NSBH (74%), Terrestrial (26%), BNS (<1%), BBH (<1%), or MassGap (<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 against matter outside the final compact object (HasRemnant: <1%). Data from the LIGO-Livingston detector at the time of the trigger exhibits non-stationarity that is consistent with a known class of transient noise [2]. Investigations are ongoing as to the possible impact of this noise feature on the significance, classification, and distance estimate of the reported trigger. 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 trigger time. For the bayestar.fits.gz,0 sky map, the 90% credible region is 24220 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 108 +/- 38 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 < https://emfollow.docs.ligo.org/userguide/>. [1] Messick et al. PRD 95, 042001 (2017) [2] Abbott et al. CQG 33, 134001 (2016)