GCN Circular 25115

The LIGO Scientific Collaboration and the Virgo Collaboration report:

We identified the compact binary merger candidate S190720a during
real-time processing of data from LIGO Hanford Observatory (H1) and
LIGO Livingston Observatory (L1) at 2019-07-20 00:08:36.704 UTC (GPS
time: 1247616534.704). The candidate was found by the PyCBC Live [1],
SPIIR [2], MBTAOnline [3], and GstLAL [4] analysis pipelines.

S190720a is an event of interest because its false alarm rate, as
estimated by the online analysis, is 3.8e-09 Hz, or about one in 8
years. The event's properties can be found at this URL:

https://gracedb.ligo.org/superevents/S190720a

Since the time of issuing the Preliminary GCN Notice at Sat 20 Jul 19
00:11:25 UTC, several other candidate events were discovered by search
pipelines. As a result, the preferred (event) data products had to be
manually selected. This caused such preferred data products (skymap,
p_astro, em_bright), as they appear in GraceDB, to change until about
the time of issuing the Initial GCN Notice at Sat 20 Jul 19 02:01:07
UTC. At the time of issuing the Initial GCN Notice and this GCN
Circular, all data products have been finalized.

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, there is strong
evidence against the lighter compact object having a mass < 3 solar
masses (HasNS: <1%). 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
[5], distributed via GCN notice about 2 hours after the candidate. This
replaces the sky map that was sent with the Preliminary GCN Notice
about 2 minutes after the candidate.

For the bayestar.fits.gz sky map, the 90% credible region is 1461
deg2. Marginalized over the whole sky, the a posteriori luminosity
distance estimate is 1071 +/- 323 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] Qi Chu, PhD Thesis, The University of Western Australia (2017)
 [3] Adams et al. CQG 33, 175012 (2016)
 [4] Messick et al. PRD 95, 042001 (2017)
 [5] Singer & Price PRD 93, 024013 (2016)