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 26640

LIGO/Virgo S200105ae: A subthreshold GW compact binary merger candidate
2020-01-06T18:25:26Z (4 years ago)
Peter Shawhan at U of Maryland/LSC <>
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:

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

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


 [1] Messick et al. PRD 95, 042001 (2017)
 [2] Singer & Price PRD 93, 024013 (2016)
Looking for U.S. government information and services? Visit