Skip to main content
Testing. You are viewing the public testing version of GCN. For the production version, go to
New Announcement Feature, Code of Conduct, Circular Revisions. See news and announcements

GCN Circular 26759

LIGO/Virgo S200115j: Identification of a GW compact binary merger candidate
2020-01-15T06:08:31Z (4 years ago)
Deep Chatterjee at University of Wisconsin, Milwaukee <>
The LIGO Scientific Collaboration and the Virgo Collaboration report:

We identified the compact binary merger candidate S200115j during
real-time processing of data from LIGO Hanford Observatory (H1), LIGO
Livingston Observatory (L1), and Virgo Observatory (V1) at 2020-01-15
04:23:09.742 UTC (GPS time: 1263097407.742). The candidate was found
by the GstLAL [1], PyCBC Live [2], MBTAOnline [3], and SPIIR [4]
analysis pipelines.

S200115j is an event of interest because its false alarm rate, as
estimated by the online analysis, is 2.1e-11 Hz, or about one in 1e3
years. The event's properties can be found at this URL:

The classification of the GW signal, in order of descending
probability, is MassGap (>99%), Terrestrial (<1%), BNS (<1%), NSBH
(<1%), or BBH (<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

Three 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
[5], distributed via GCN notice about 6 minutes after the candidate
event time.
 * bayestar.fits.gz,1, an initial localization generated by BAYESTAR
[5], distributed via GCN notice about 12 minutes after the candidate
event time.
 * bayestar.fits.gz,2, an initial localization generated by BAYESTAR
[5], distributed via GCN notice about an hour after the candidate
event time.

The preferred sky map at this time is bayestar.fits.gz,2. For the
bayestar.fits.gz,2 sky map, the 90% credible region is 908 deg2.
Marginalized over the whole sky, the a posteriori luminosity distance
estimate is 331 +/- 97 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

 [1] Messick et al. PRD 95, 042001 (2017)
 [2] Nitz et al. PRD 98, 024050 (2018)
 [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)
Looking for U.S. government information and services? Visit