GCN Circular 19341

The LIGO Scientific Collaboration and Virgo report:

The offline gstlal and pycbc CBC analyses identified candidate G197392,
also known as LVT (LIGO/Virgo Trigger) 151012, during offline processing
of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory
(L1) at 2015-10-12 09:54:43.444 UTC (GPS time: 1128678900.444).

The candidate's false alarm rate was reported as 1 per 2.3 years and a
corresponding false alarm probability of 0.02 (2.1 sigma) in LSC+Virgo
2016a (http://adsabs.harvard.edu/abs/2016PhRvL.116f1102A) and LSC+Virgo
2016b (http://adsabs.harvard.edu/abs/2016arXiv160203839T). There is an
80--90% chance that the signal has an astrophysical origin. If it does,
then the source is a binary black hole merger.

LVT151012 was not recovered in real time because the template banks for
the low-latency CBC searches were not configured at the time to include
BBHs, and the signal was too weak to be detected by the un-modeled burst
searches. The offline significance estimate makes it an event of interest
because it passes our stated alert threshold of ~1/month.

The event's properties can be found at this URL:

https://gracedb.ligo.org/events/G197392

The available sky map, LALInference_skymap.fits.gz, was generated using
Bayesian Markov-chain Monte Carlo and nested sampling to perform forward
modeling of the full GW signal including the inspiral and merger as well
as the effects of calibration uncertainty. The localization is mainly
determined by the 0.6-ms time delay on arrival of the signal between H1 and
L1. It favors two long islands on opposite sides of a roughly 2 deg wide
annulus. The 90% credible region spans an area of about 1700 deg2. We
regard this sky map as the most accurate to date for this event.

The BAYESTAR localization derived from triangulation of times, amplitudes,
and phases on arrival is qualitatively and quantitatively consistent with
the LALInference sky map. The localizations produced by the cWB and LIB
un-modeled burst analyses are significantly coarser due to the low
signal-to-noise ratio, but they are qualitatively consistent with
the CBC localizations.