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GCN Circular 20364

Subject
LIGO/Virgo G268556: Identification of a GW CBC Candidate
Date
2017-01-04T16:49:56Z (7 years ago)
From
Peter Shawhan at U of Maryland/LSC <pshawhan@umd.edu>
The LIGO Scientific Collaboration and Virgo report:

The online pycbc CBC analysis identified a candidate with GraceDB ID
G268556 during processing of data from LIGO Hanford Observatory (H1)
and LIGO Livingston Observatory (L1) at 2017-01-04 10:11:58.599 UTC
(GPS time: 1167559936.599).

G268556 is an event of interest because its false alarm rate, as
determined by preliminary analysis, is less than (i.e., more significant
than) 6.1e-08 Hz (about one in 6 months). The event's properties can be
found at this URL:

https://gracedb.ligo.org/events/G268556

Based on preliminary matched-filter estimates of the masses and spins,
there is a 0% chance that the less massive companion in the binary has
a mass less than 3 Msun. Based on the tidal disruption condition and disk
mass formula of Foucart (PRD 86, 124007), using an implementation
based on Pannarale & Ohme (ApJL 791, 7), we estimate that there is a
0% chance that the system ejected enough neutron-rich material to power
an electromagnetic transient.

One sky map with distance information (e.g., Singer et al. 2016, ApJL 829,
15) is available at this time and can be retrieved from the GraceDB event
page: bayestar.fits.gz, an initial localization generated by the BAYESTAR
pipeline. The probability is concentrated in two long, thin arcs.  The 50%
credible region spans about 400 deg2 and the 90% region about 1600 deg2.
This is the preferred sky map at this time.

This event was also detected by the cWB unmodeled burst search, with a
sky map consistent with the one from BAYESTAR.

The event candidate was not reported by the low-latency analysis pipelines
because re-tuning the calibration of the LIGO Hanford detector is not yet
complete after the holiday shutdown. This resulted in a delay of over 4
hours
before the candidate could be fully examined. We are confident that this is
a
highly significant event candidate, but the calibration issue may be
affecting
the initial sky maps. We will provide an update in approximately 48 hours
which may include an improved sky map.
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