GCN Circular 18889

The LIGO Scientific Collaboration and Virgo report:

We have completed a Bayesian parameter estimation analysis of the GW
candidate G211117 (GCN 18728
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 ) under the assumption that the signal arises
from a compact binary coalescence (CBC) and using the initial online
calibration of the GW strain data. The data is most consistent with a
binary black hole merger.

One refined sky map is now available and can be retrieved from
GraceDB (https://gracedb.ligo.org/events/G211117):

 * LALInference_skymap.fits.gz, using Bayesian Markov-chain Monte Carlo
   and nested sampling to perform forward modeling of the full GW signal
   including spin precession and regression of systematic calibration
   errors. We expect that additional parameter estimation runs based on
   the offline re-calibration of the GW data and additional waveform
   approximants will yield consistent results. We regard this sky map as
   the most accurate to date for this event.

This sky map agrees with the initial BAYESTAR and cWB localizations on
favoring two broad, disjoint segments of an annulus.

The table below presents a quantitative comparison of the available
localizations along the lines of Sec. 4.5 of Essick et al. (2015,
http://adsabs.harvard.edu/abs/2015ApJ...800...81E). The first column gives
the area in deg2 of the 90% credible region, and the second column gives
the area in deg2 of the overlap with the LALInference 90% credible region.

 Area  Overlap   Algorithm (filename)         
-------------------------------------------------------------
 1340   1090     BAYESTAR (bayestar.fits.gz)
 2230   1180     cWB (skyprobcc_cWB.fits)
 1240   ----     LALInference (LALInference_skymap.fits.gz)