GCN Circular 26906

The LIGO Scientific Collaboration and the Virgo Collaboration report:

We identified the compact binary merger candidate S200128d during
real-time processing of data from LIGO Hanford Observatory (H1) and
LIGO Livingston Observatory (L1) at 2020-01-28 02:20:11.903 UTC (GPS
time: 1264213229.903). The candidate was found by the PyCBC Live [1],
CWB [2], MBTAOnline [3], and GstLAL [4] analysis pipelines.

S200128d is an event of interest because its false alarm rate, as
estimated by the online analysis, is 1.6e-08 Hz, or about one in 1
year, 11 months. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S200128d

The classification of the GW signal, in order of descending
probability, is BBH (97%), Terrestrial (3%), BNS (<1%), NSBH (<1%), or
MassGap (<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 3 minutes after the candidate
event time.
 ��* bayestar.fits.gz,1, an initial localization generated by BAYESTAR
[5], 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 2521 deg2.
Marginalized over the whole sky, the a posteriori luminosity distance
estimate is 4031 +/- 1241 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] Nitz et al. PRD 98, 024050 (2018)
[2] Klimenko et al. PRD 93, 042004 (2016)
[3] Adams et al. CQG 33, 175012 (2016)
[4] Messick et al. PRD 95, 042001 (2017)
[5] Singer & Price PRD 93, 024013 (2016)