GCN Circular 27278

The LIGO Scientific Collaboration and the Virgo Collaboration report:

We identified the compact binary merger candidate S200302c during
real-time processing of data from LIGO Hanford Observatory
(H1) and Virgo Observatory (V1) at 2020-03-02 01:58:11.519 UTC (GPS
time: 1267149509.519). The candidate was found by the GstLAL [1]
analysis pipeline.

S200302c is an event of interest because its false alarm rate, as
estimated by the online analysis, is 9.3e-09 Hz, or about one in 3
years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S200302c

The classification of the GW signal, in order of descending
probability, is BBH (89%), Terrestrial (11%), 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
[2], distributed via GCN notice about a minute after the candidate
event time.
 * bayestar.fits.gz,1, distributed via GCN notice about 7 minutes after
the candidate event time.  (This is identical to bayestar.fits.gz,0 )

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 6704 deg2.
Marginalized over the whole sky, the a posteriori luminosity distance
estimate is 1737 +/- 500 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] Singer & Price PRD 93, 024013 (2016)