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GCN Circular 20385

Subject
LIGO/Virgo G268556: Updated sky map from gravitational-wave data
Date
2017-01-06T21:44:29Z (7 years ago)
From
Giuseppe Greco at U degli Studi di Urbino <giuseppe.greco@uniurb.it>
The LIGO Scientific Collaboration and Virgo report:

We have re-analyzed LIGO data around the time of the compact binary
coalescence (CBC) event candidate G268556 (GCN 20364) taking into account
our current understanding of calibration uncertainties.  Although a full
recalibration remains to be done, we expect that this event will be
confirmed with a false alarm rate (FAR) of less than 1 per 100 years.

Parameter estimation has been performed using LALInference (Veitch et al.,
PRD 91, 042003) and a new sky map, LALInference_skymap.fits.gz, is
available for retrieval from the GraceDB event page:

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

This is the preferred sky map at this time.  This map has two arcs in
nearly the same positions as the original BAYESTAR sky map but the
probability is divided more equally between the northern and southern
arcs.  The 50% and 90% credible regions span about 500 deg2 and 2000 deg2,
respectively, which are somewhat larger than the initial BAYESTAR sky map
due to marginalizing over calibration uncertainties.

We will recalculate the sky map once the full recalibration is complete
and will share it at that time, but that is likely at least a few weeks
away.
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