TITLE:   GCN CIRCULAR
NUMBER:  27382
SUBJECT: LIGO/Virgo S200311bg: Updated Sky Localization and EM Bright Classification
DATE:    20/03/13 15:12:55 GMT
FROM:    Geoffrey Mo at MIT  <gmo@mit.edu>

The LIGO Scientific Collaboration and the Virgo Collaboration report:

We have conducted further analysis of the LIGO Hanford Observatory
(H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1)
data around the time of the compact binary merger (CBC) candidate
S200311bg (GCN Circular 27358).
Parameter estimation has been performed using LALInference [1] and a
new sky map, LALInference.fits.gz,0, distributed via GCN Notice, is
available for retrieval from the GraceDB event page:

https://gracedb.ligo.org/superevents/S200311bg

The preferred sky map at this time is LALInference.fits.gz,0. For the
LALInference.fits.gz,0 sky map, the 90% credible region is well fit by
an ellipse with an area of 34 deg2 described by the following DS9
region (right ascension, declination, semi-major axis, semi-minor
axis, position angle of the semi-minor axis):
   icrs; ellipse(00h09m, -08d14m, 6.91d, 1.59d, 72.77d)
Marginalized over the whole sky, the a posteriori luminosity distance
estimate is 1115 +/- 175 Mpc (a posteriori mean +/- standard
deviation).

Based on posterior support from parameter estimation [1], under the
assumption that the candidate S200311bg is astrophysical in origin,
the probability that the lighter compact object has a mass < 3 solar
masses (HasNS) is <1%. Using the masses and spins inferred from the
signal, the probability of matter outside the final compact object
(HasRemnant) is <1%.

For further information about analysis methodology and the contents of
this alert, refer to the LIGO/Virgo Public Alerts User Guide
<https://emfollow.docs.ligo.org/userguide/>.

 [1] Veitch et al. PRD 91, 042003 (2015)