GCN Circular 25503

The LIGO Scientific Collaboration and the Virgo Collaboration report:


We identified the compact binary merger candidate S190828l during
real-time processing of data from LIGO Hanford Observatory (H1), LIGO
Livingston Observatory (L1), and Virgo Observatory (V1) at 2019-08-28
06:55:09.887 UTC (GPS time: 1251010527.887). The candidate was found
by the GstLAL [1], MBTAOnline [2], SPIIR [3], and PyCBC Live [4]
analysis pipelines.

Note that S190828l and S190828j (GCN 25497
Not found
 
 
) are distinct events that
occurred 21 minutes apart.

S190828l is an event of interest because its false alarm rate, as
estimated by the online analysis, is 4.6e-11 Hz, or about one in 700
years. The event's properties can be found at this URL:

https://gracedb.ligo.org/superevents/S190828l

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
[5], distributed via GCN notice about 22 minutes after the candidate

For the bayestar.fits.gz sky map, the 90% credible region is 948 deg2.
Marginalized over the whole sky, the a posteriori luminosity distance
estimate is 1609 +/- 426 Mpc (a posteriori mean +/- standard
deviation).

The localizations of S190828j and S190828l strongly resemble each
other. This is not unexpected for events occurring at similar times
because the detector sensitivity antenna patterns rotate with the
Earth. The two localizations are definitely disjoint: their
prevailing triangulation annuli are separated by over 10 degrees.

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] Adams et al. CQG 33, 175012 (2016)
 [3] Qi Chu, PhD Thesis, The University of Western Australia (2017)
 [4] Nitz et al. PRD 98, 024050 (2018)
 [5] Singer & Price PRD 93, 024013 (2016)