GCN Circular 26926

The LIGO Scientific Collaboration and the Virgo Collaboration report:

We identified the compact binary merger candidate S200129m during
real-time processing of data from LIGO Hanford Observatory (H1), LIGO
Livingston Observatory (L1), and Virgo Observatory (V1) at 2020-01-29
06:54:58.435 UTC (GPS time: 1264316116.435). The candidate was found
by the GstLAL [1], CWB [2], PyCBC Live [3], MBTAOnline [4], and SPIIR [5]
analysis pipelines.

Some scattering noise could be seen around the time of the event in
Virgo data; follow-up studies are on-going. We will update the localization if
warranted by offline analysis.

S200129m is an event of interest because its false alarm rate, as
estimated by the online analysis, is 6.7e-32 Hz, or about one in 1e23
years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S200129m

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
[6], distributed via GCN notice about 4 minutes after the candidate
event time.
 * bayestar.fits.gz,1, an initial localization generated by BAYESTAR
[6], distributed via GCN notice about 13 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 53 deg2.
Marginalized over the whole sky, the a posteriori luminosity distance
estimate is 908 +/- 202 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] Nitz et al. PRD 98, 024050 (2018)
 [4] Adams et al. CQG 33, 175012 (2016)
 [5] Qi Chu, PhD Thesis, The University of Western Australia (2017)
 [6] Singer & Price PRD 93, 024013 (2016)