# GCN Circular 26350

**Subject**

LIGO/Virgo S191205ah: Identification of a GW compact binary merger candidate

**Date**

2019-12-05T22:35:27Z (5 years ago)

**From**

Deep Chatterjee at University of Wisconsin, Milwaukee <deep@uwm.edu>

```
The LIGO Scientific Collaboration and the Virgo Collaboration report:
We identified the compact binary merger candidate S191205ah during
real-time processing of data from LIGO Hanford Observatory (H1), LIGO
Livingston Observatory (L1), and Virgo Observatory (V1) at 2019-12-05
21:52:08.569 UTC (GPS time: 1259617946.569). The candidate was found
by the GstLAL [1] analysis pipeline.
S191205ah is an event of interest because its false alarm rate, as
estimated by the online analysis, is 1.2e-08 Hz, or about one in 2
years. The event's properties can be found at this URL:
https://gracedb.ligo.org/superevents/S191205ah
The classification of the GW signal, in order of descending
probability, is NSBH (93%), Terrestrial (7%), BNS (<1%), BBH (<1%), or
MassGap (<1%).
Assuming the candidate is astrophysical in origin, the probability
that the lighter compact object has a mass < 3 solar masses (HasNS) is
>99%. Using the masses and spins inferred from the signal, the
probability of matter outside the final compact object (HasRemnant) is
<1%.
Two sky maps are available at this time and can be retrieved from the
GraceDB event page:
* bayestar.fits.gz,0, an initial localization generated by BAYESTAR
[2], distributed via GCN notice about 2 minutes after the candidate
event time.
* bayestar.fits.gz,1, an initial localization generated by BAYESTAR
[2], distributed via GCN notice about 8 minutes after the candidate
event time.
The preferred sky map at this time is bayestar.fits.gz,1. For the
bayestar.fits.gz,1 sky map, the 90% credible region is 6378 deg2.
Marginalized over the whole sky, the a posteriori luminosity distance
estimate is 385 +/- 164 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] Singer & Price PRD 93, 024013 (2016)
```