GCN Circular 27184

We identified the compact binary merger candidate S200224ca during
real-time processing of data from LIGO Hanford Observatory (H1),LIGO
Livingston Observatory (L1), and Virgo Observatory (V1) at 2020-02-24
22:22:34.406 UTC (GPS time: 1266618172.406). The candidate was found
by the PyCBC Live [1], CWB [2], GstLAL [3], MBTAOnline [4] ,and SPIIR [5]
analysis pipelines.

S200224ca is an event of interest because its false alarm rate, as
estimated by the online analysis, is 1.6e-11 Hz, or about one in 1e3
years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S200224ca

The classification of the GW signal, in order of descending
probability, is BBH (>99%), Terrestrial (<1%), 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
[6], distributed via GCN notice about 3 minutes after the candidate
event time.
 * bayestar.fits.gz,1, an initial localization generated by BAYESTAR
[6], distributed via GCN notice about 10 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 well fit by an
ellipse with an area of 73 deg2 described by the following DS9 region
(right ascension, declination, semi-major axis, semi-minor axis,
position angle of the semi-minor axis):
   icrs; ellipse(11h38m42s, -09d20m21s, 9d, 3d, 68d)
Marginalized over the whole sky, the a posteriori luminosity distance
estimate is 1585 +/- 331 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] Messick et al. PRD 95, 042001 (2017)
 [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) [7] Singer & Price PRD 93,
024013 (2016)