GCN Circular 25707

The LIGO Scientific Collaboration and the Virgo Collaboration report:

We identified the compact binary merger candidate S190910h during
real-time processing of data from LIGO Livingston Observatory (L1) at
2019-09-10 08:29:58.544 UTC (GPS time: 1252139416.544). The candidate
was found by the GstLAL [1] analysis pipeline.

S190910h is an event of interest because its false alarm rate, as
estimated by the online analysis, is 3.6e-08 Hz, or about one in 10
months. The event's properties can be found at this URL:

https://gracedb.ligo.org/superevents/S190910h

The classification of the GW signal, in order of descending
probability, is BNS (61%), Terrestrial (39%), BBH (<1%), MassGap
(<1%), or NSBH (<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 for matter outside the final compact object
(HasRemnant: >99%).

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
[2], distributed via GCN notice about 6 minutes after the candidate

For the bayestar.fits.gz sky map, the 90% credible region is 24226
deg2. Marginalized over the whole sky, the a posteriori luminosity
distance estimate is 241 +/- 89 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)