GCN Circular 20840
The LIGO Scientific Collaboration and Virgo report: We have completed an initial Bayesian parameter estimation analysis of the LIGO data around the time of the compact binary coalescence (CBC) event candidate G275404 (GCN 20738) using LALInference (Veitch et al., PRD 91, 042003). This analysis used the IMRPhenomPv2 waveform approximation, which includes the inspiral, merger, and ringdown phases of the signal and accounts for the effects of spin precession. We accounted for systematic errors due to uncertainty in the calibration of the detectors' responses of up to 10% in amplitude and 10 degrees in phase. This follow-up analysis also used different, more conservative assumptions on the detector noise properties. The updated localization, LALInference.fits.gz, is available for retrieval from the GraceDB event page: https://gracedb.ligo.org/events/G275404 <https://gracedb.ligo.org/events/G275404> The localization has arcs similar to the rapid BAYESTAR sky map, but broader, and the conservative assumptions mentioned above result in this case in a much larger area in the sky consistent with the observed data. The 50% credible region spans 2000 deg2 and the 90% credible region spans 17000 deg2 due to a diffuse component in the probability distribution. This parameter estimation analysis does not influence our estimation of the significance of this event. It remains a marginal candidate with a false alarm rate of about one in two months as reported in our original Circular. If the signal is astrophysical, then the mass estimates are consistent with a NSNS or NSBH binary.