The LIGO Scientific Collaboration and the Virgo Collaboration report:
We identified the compact binary merger candidate S191213g during
real-time processing of data from LIGO Hanford Observatory (H1), LIGO
Livingston Observatory (L1), and Virgo Observatory (V1) at 2019-12-13
04:34:08.142 UTC (GPS time: 1260246866.142). The candidate was found
by the GstLAL  analysis pipeline.
S191213g is an event of interest because its false alarm rate, as
estimated by the online analysis, is 3.5e-08 Hz, or about one in 10
months. The event's properties can be found at this URL:
The classification of the GW signal, in order of descending
probability, is BNS (77%), Terrestrial (23%), BBH (<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
>99%. Using the masses and spins inferred from the signal, the
probability of matter outside the final compact object (HasRemnant) is
During the time period that the candidate signal was in band of the
detector, multiple cases of scattered light glitches
were present in both the H1 and L1 detectors, overlapping the
frequency band of the candidate. These artifacts may have
impacted the estimated significance and sky position of the event.
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
, distributed via GCN notice about 5 minutes after the candidate
* bayestar.fits.gz,1, an initial localization generated by BAYESTAR
, distributed via GCN notice about 11 minutes after the candidate
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 1393 deg2.
Marginalized over the whole sky, the a posteriori luminosity distance
estimate is 195 +/- 59 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
 Messick et al. PRD 95, 042001 (2017)
 Singer & Price PRD 93, 024013 (2016)