GCN Circular 26303

The LIGO Scientific Collaboration and the Virgo Collaboration report:

We identified the compact binary merger candidate S191129u during
real-time processing of data from LIGO Hanford Observatory (H1) and
LIGO Livingston Observatory (L1) at 2019-11-29 13:40:29.197 UTC (GPS
time: 1259070047.197). The candidate was found by the GstLAL [1],
MBTAOnline [2], SPIIR [3], and PyCBC Live [4] analysis pipelines.

S191129u is an event of interest because its false alarm rate, as
estimated by the online analysis, is 2.7e-35 Hz, or about one in 1e27
years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S191129u

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%.

One sky map is available at this time and can be retrieved from the
GraceDB event page:
 * bayestar.fits.gz,0, an initial localization generated by BAYESTAR
[5], distributed via GCN notice about 42 minutes after the candidate
event time.

For the bayestar.fits.gz,0 sky map, the 90% credible region is 1011
deg2. Marginalized over the whole sky, the a posteriori luminosity
distance estimate is 763 +/- 200 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] Adams et al. CQG 33, 175012 (2016)
 [3] Qi Chu, PhD Thesis, The University of Western Australia (2017)
 [4] Nitz et al. PRD 98, 024050 (2018)
 [5] Singer & Price PRD 93, 024013 (2016)