GCN Circular 25497

The LIGO Scientific Collaboration and the Virgo Collaboration report:

We identified the compact binary merger candidate S190828j during
real-time processing of data from LIGO Hanford Observatory (H1), LIGO
Livingston Observatory (L1), and Virgo Observatory (V1) at 2019-08-28
06:34:05.756 UTC (GPS time: 1251009263.756). The candidate was found
by the GstLAL [1], CWB [2], PyCBC Live [3], MBTAOnline [4], and SPIIR
[5] analysis pipelines.

S190828j is an event of interest because its false alarm rate, as
estimated by the online analysis, is 8.5e-22 Hz, or about one in 1e14
years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S190828j

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, 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
[6], distributed via GCN notice about 16 minutes after the candidate

For the bayestar.fits.gz sky map, the 90% credible region is 603 deg2.
Marginalized over the whole sky, the a posteriori luminosity distance
estimate is 2276 +/- 538 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)