GCN Circular 25695

The LIGO Scientific Collaboration and the Virgo Collaboration report:

We identified the compact binary merger candidate S190910d during
real-time processing of data from LIGO Hanford Observatory (H1) and
LIGO Livingston Observatory (L1) at 2019-09-10 01:26:19.243 UTC (GPS
time: 1252113997.243). The candidate was found by the SPIIR [1] and
MBTAOnline [2] analysis pipelines.

S190910d is an event of interest because its false alarm rate, as
estimated by the online analysis, is 3.7e-09 Hz, or about one in 8
years. The event's properties can be found at this URL:

https://gracedb.ligo.org/superevents/S190910d

The classification of the GW signal, in order of descending
probability, is NSBH (98%), Terrestrial (2%), BNS (<1%), BBH (<1%), or
MassGap (<1%).

Assuming the candidate is astrophysical in origin, there is strong
evidence for the lighter compact object having a mass < 3 solar masses
(HasNS: >99%). Using the masses and spins inferred from the signal,
there is strong evidence against matter outside the final compact
object (HasRemnant: <1%).

One sky map is available at this time and can be retrieved from the
GraceDB event page:
 * bayestar.fits.gz, an updated localization generated by BAYESTAR
[3], distributed via GCN notice about 6 minutes after the candidate

For the bayestar.fits.gz sky map, the 90% credible region is 3829
deg2. Marginalized over the whole sky, the a posteriori luminosity
distance estimate is 606 +/- 197 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] Qi Chu, PhD Thesis, The University of Western Australia (2017)
 [2] Adams et al. CQG 33, 175012 (2016)
 [3] Singer & Price PRD 93, 024013 (2016)