GCN Circular 26543

The LIGO Scientific Collaboration and the Virgo Collaboration report:

We identified the compact binary merger candidate S191222n during
real-time processing of data from LIGO Hanford Observatory (H1) and
LIGO Livingston Observatory (L1) at 2019-12-22 03:35:37.119 UTC (GPS
time: 1261020955.119). The candidate was found by the GstLAL [1],
SPIIR [2], and CWB [3] analysis pipelines.

S191222n is an event of interest because its false alarm rate, as
estimated by the online analysis, is 6.5e-12 Hz, or about one in 5e3
years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S191222n

The classification of the GW signal, in order of descending
probability, is BBH (>99%), Terrestrial (<1%), BNS (<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
<1%. Using the masses and spins inferred from the signal, the
probability of matter outside the final compact object (HasRemnant) is
<1%.

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
[4], distributed via GCN notice about 3 minutes after the candidate
event time.
 ��* bayestar.fits.gz,1, an initial localization generated by BAYESTAR
[4], distributed via GCN notice about 9 minutes after the candidate
event time.

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 2324 deg2.
Marginalized over the whole sky, the a posteriori luminosity distance
estimate is 868 +/- 265 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] Qi Chu, PhD Thesis, The University of Western Australia (2017)
 ��[3] Klimenko et al. PRD 93, 042004 (2016)
 ��[4] Singer & Price PRD 93, 024013 (2016)