TITLE:   GCN CIRCULAR
NUMBER:  20833
SUBJECT: LIGO/Virgo G275697: Updated localization from LIGO data
DATE:    17/03/07 20:44:12 GMT
FROM:    Leo Singer at NASA/GSFC  <leo.p.singer@nasa.gov>

The LIGO Scientific Collaboration and Virgo report:

We have completed an initial Bayesian parameter estimation analysis of the
LIGO data around the time of the compact binary coalescence (CBC) event
candidate G275697 (GCN 20763) using LALInference (Veitch et al., PRD 91,
042003). This analysis used the IMRPhenomPv2 waveform approximant, which
includes the inspiral, merger, and ringdown phases of the signal and
accounts for the effects of spin precession. We accounted for systematic
errors due to uncertainty in the calibration of the detectors' responses
of up to 10% in amplitude and 10 degrees in phase.

This parameter estimation analysis does not influence our estimation of
the significance of this event. It remains a marginal candidate with a
false alarm rate of about one in two months as reported in our original
Circular. If the signal is astrophysical, then the mass estimates are
consistent with a NSNS or NSBH binary.

An updated localization, LALInference.fits.gz, is available for retrieval
from the GraceDB event page:

https://gracedb.ligo.org/events/G275697

This is the preferred sky map at this time. The localization is similar to
the rapid BAYESTAR sky map, but it is coarser due to the inclusion of
systematic errors due to calibration. The 50% credible region spans 1020
deg2 and the 90% credible region spans 3890 deg2. The luminosity distance
is found to be 193 +/- 61 Mpc (mean +/- std. dev.).

Further updates on our analysis of this event will be sent as they become
available.