GCN Circular 25876

The LIGO Scientific Collaboration and the Virgo Collaboration report:

We identified the compact binary merger candidate S190930t during real-time
processing of data from LIGO Livingston Observatory (L1) at 2019-09-30
14:34:07.685 UTC (GPS time: 1253889265.685). The candidate was found by the
GstLAL [1] analysis pipeline.

S190930t is an event of interest because its false alarm rate, as estimated
by the online analysis, is 1.5e-08 Hz, or about one in 2 years. The event's
properties can be found at this URL:

https://gracedb.ligo.org/superevents/S190930t

The classification of the GW signal, in order of descending probability, is
NSBH (74%), Terrestrial (26%), BNS (<1%), BBH (<1%), or MassGap (<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 against matter outside the final compact object (HasRemnant: <1%).

Data from the LIGO-Livingston detector at the time of the trigger exhibits
non-stationarity that is consistent with a known class of transient noise
[2]. Investigations are ongoing as to the possible impact of this noise
feature on the significance, classification, and distance estimate of the
reported trigger.

One sky map is available at this time and can be retrieved from the GraceDB
event page: * bayestar.fits.gz,0, an updated localization generated by
BAYESTAR [5], distributed via GCN notice about 6 minutes after the
candidate trigger time. For the bayestar.fits.gz,0 sky map, the 90%
credible region is 24220 deg2. Marginalized over the whole sky, the a
posteriori luminosity distance estimate is 108 +/- 38 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] Abbott et al. CQG 33, 134001 (2016)