GCN Circular 25187

The LIGO Scientific Collaboration and the Virgo Collaboration report:

We identified the compact binary merger candidate S190728q during
real-time processing of data from LIGO Hanford Observatory (H1), LIGO
Livingston Observatory (L1), and Virgo Observatory (V1) at 2019-07-28
06:45:10.529 UTC (GPS time: 1248331528.529). The candidate was found
by the GstLAL [1], CWB [2], MBTAOnline [3], and SPIIR [4] analysis
pipelines.

S190728q is an event of interest because its false alarm rate, as
estimated by the online analysis, is 2.5e-23 Hz, or about one in 1e15
years. The event's properties can be found at this URL:

https://gracedb.ligo.org/superevents/S190728q

The classification of the GW signal, in order of descending
probability, is MassGap (52%), BBH (34%), NSBH (14%), Terrestrial
(<1%), or BNS (<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 55 minutes after the candidate

For the bayestar.fits.gz sky map, the 90% credible region is 543 deg2.
Marginalized over the whole sky, the a posteriori luminosity distance
estimate is 795 +/- 197 Mpc (a posteriori mean +/- standard
deviation).

Note that both skymap and source-classification were updated for
the event in favor of a triple detector event.

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