GCN Circular 26441

The LIGO Scientific Collaboration and the Virgo Collaboration report:

We identified the compact binary merger candidate S191215w during
real-time processing of data from LIGO Hanford Observatory (H1), LIGO
Livingston Observatory (L1), and Virgo Observatory (V1) at 2019-12-15
22:30:52.333 UTC (GPS time: 1260484270.333). The candidate was found
by the GstLAL [1], CWB [2], MBTAOnline [3], and PyCBC Live [4]
analysis pipelines.

S191215w is an event of interest because its false alarm rate, as
estimated by the online analysis, is 1e-09 Hz, or about one in 31
years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S191215w

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
[5], distributed via GCN notice about 7 minutes after the candidate
event time.
  * bayestar.fits.gz,1, an initial localization generated by BAYESTAR
[5], distributed via GCN notice about 15 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 923 deg2.
Marginalized over the whole sky, the a posteriori luminosity distance
estimate is 2216 +/- 590 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] Klimenko et al. PRD 93, 042004 (2016)
  [3] Adams et al. CQG 33, 175012 (2016)
  [4] Nitz et al. PRD 98, 024050 (2018)
  [5] Singer & Price PRD 93, 024013 (2016)