TITLE:   GCN CIRCULAR
NUMBER:  26807
SUBJECT: LIGO/Virgo S200115j: Updated Sky Localization and source properties
DATE:    20/01/17 18:50:16 GMT
FROM:    Deep Chatterjee at University of Wisconsin, Milwaukee  <deep@uwm.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
S200115j (GCN Circular 26759). 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/S200115j/files/

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 765 deg2.
Marginalized over the whole sky, the a posteriori luminosity distance
estimate is 340 +/- 79 Mpc (a posteriori mean +/- standard deviation).

Based on posterior support from parameter estimation [1], under the
assumption that the candidate is astrophysical in origin, the
probability that the lighter compact object has a mass < 3 solar
masses (HasNS) is >99%. Using the masses and spins inferred from the
signal, the probability of matter outside the final compact object
(HasRemnant) is >99%.

Note: the sequence of three Preliminary Notices on January 15, 2020
for this candidate was due to a manual change in the
"preferred event". The MBTAOnline pipeline found the largest
signal-to-noise ratio (SNR) and thus provided the first preferred
event, as indicated in the first two Preliminary Notices. However, the
preferred event was manually changed to a GstLAL trigger (with nearly
the same SNR) because of a possible discrepancy noted in the
low-latency Bayestar sky maps calculated for the two triggers. The
third Preliminary Notice reflected that change.

For further information about analysis methodology including
“preferred events”, refer to the LIGO/Virgo Public Alerts User Guide
<https://emfollow.docs.ligo.org/userguide/>.

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