Skip to main content
Introducing Einstein Probe, Astro Flavored Markdown, and Notices Schema v4.0.0. See news and announcements

GCN Circular 18442

LIGO/Virgo G194575: Identification of a GW CBC Candidate
2015-10-22T20:03:45Z (9 years ago)
Leo Singer at NASA/GSFC <>
Leo Singer (NASA/GSFC), Peter Shawhan (UMD), Nipuni Palliyaguru (TTU), B.
S. Sathyaprakash (Cardiff), Alex Urban (UWM), Jeff Bartlett (LIGO
Hanford), Travis Sadecki (LIGO Hanford), Mike Landry (LIGO Hanford), Joe
Hanson (LIGO Livingston), Bryan Smith (LIGO Livingston), Brian O'Reilly
(LIGO Livingston), Kipp Cannon (CITA), Gianluca Guidi (Urbino), Andy
Lundgren (AEI/Hannover), Laura Nuttall (Syracuse), T. J. Massinger
(Syracuse), Jessica McIver (Caltech), and Joshua Smith (Fullerton) report
on behalf of the LIGO Scientific Collaboration and Virgo:

The gstlal CBC analysis, which is sensitive to binary coalescence events
from systems containing at least one neutron star, identified candidate
G194575 during real-time processing of data from LIGO Hanford Observatory
(H1) and LIGO Livingston Observatory (L1) at 2015-10-22 13:33:19.942 UTC
(GPS time: 1129556016.942). Both the H1 and L1 detectors were in
observation mode and operating normally.

G194575 is an event of interest because its false alarm rate, as
determined by the online analysis, is 9.65e-08 Hz or about one in 4
months, passing our stated alert threshold of ~1/month for CBC candidates.
The event's properties can be found at this URL:

Fermi triggered (bn151022577) about 1 ks after the LIGO candidate, and
Swift detected GRB 151022A (D���Avanzo et al., GCN 18436) about 2 ks after.
Neither gamma-ray trigger���s localization is consistent with the rapid
position reconstruction of the LIGO candidate. Based on the separation in
time and sky position, we infer that these high-energy triggers are

One sky map is available at this time and can be retrieved from the
GraceDB event page: skymap.fits.gz, an initial localization generated by
BAYESTAR. The probability is concentrated in two main equatorial regions
around right ascensions of 1h and 13h. About 30% of the probability is
confined to the top 500 deg2.

Updates on our analysis of this event will be sent as they become
Looking for U.S. government information and services? Visit