GCN Circular 20860

The LIGO Scientific Collaboration and Virgo report:

The CWB Burst analysis identified candidate G277583 during real-time
processing of data from LIGO Hanford Observatory (H1) and LIGO
Livingston Observatory (L1) at 2017-03-13 22:40:09.593 UTC (GPS time:
1173480027.593).

G277583 is an event of interest because its false alarm rate, as
determined by the online analysis, is 8.4e-08 Hz or about one in 4
months. The event's properties can be found at this URL:

https://gracedb.ligo.org/events/G277583

Two sky maps are available at this time and can be retrieved from
the GraceDB event page:
  *skyprobcc_cWB.fits, an initial localization generated by cWB,
   included in the original GCN notice.
  *cWB_plus_LIB.fits.gz, a pixel-by-pixel arithmetic mean of the
   cWB and LIB sky maps. Since neither cWB nor LIB is favored
   over the other, this mean sky map is the preferred sky map at
   this time. The 50% confidence interval covers 2130 squares
   degrees and the 90% confidence interval covers 12140 square
   degrees.

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