TITLE:   GCN CIRCULAR
NUMBER:  26640
SUBJECT: LIGO/Virgo S200105ae: A subthreshold GW compact binary merger candidate
DATE:    20/01/06 18:25:26 GMT
FROM:    Peter Shawhan at U of Maryland/LSC  <pshawhan@umd.edu>

The LIGO Scientific Collaboration and the Virgo Collaboration report:

We identified the compact binary merger candidate S200105ae in data
from LIGO Livingston Observatory (L1) and Virgo Observatory (V1) at
2020-01-05 16:24:26.057 UTC (GPS time: 1262276684.057). The candidate
was found by the GstLAL [1] analysis pipeline. LIGO Hanford
Observatory (H1) was offline at the time.

The signal-to-noise ratio (SNR) was below threshold in V1 so the
candidate was treated as a single-instrument event. The false alarm
rate (FAR) estimated from the L1 trigger, 7.6e-07 Hz -- or about 24
per year -- was above the threshold we normally use for issuing a
public alert.  However, after further offline analysis of the
candidate, we believe that its significance is greater than that
calculated in real-time processing.  Follow-up observations may
therefore be justified.

The event's properties can be found at this URL:

https://gracedb.ligo.org/superevents/S200105ae

We cannot quantify the probability of this event being astrophysical
at this time.  However, if it is astrophysical, it is most consistent
with being a neutron star - black hole (NSBH) event.  Under this
assumption, 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, it is possible but unlikely that the
merger left matter outside the final compact object.  (HasRemnant was
estimated as 12% by the initial analysis, but this value is considered
uncertain.)

One sky map is available at this time and can be retrieved from the
GraceDB event page:
 * bayestar.fits.gz,0, an initial localization generated by BAYESTAR [2].
No GCN notice has been issued for this candidate.

For the bayestar.fits.gz sky map, the 90% credible region is 7719
deg2, dominated by the L1 antenna response. Marginalized over the
whole sky, the a posteriori luminosity distance estimate is 265 +/- 71
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)