TITLE:   GCN CIRCULAR
NUMBER:  20422
SUBJECT: LIGO/Virgo G268556: Swift/BAT data search
DATE:    17/01/11 00:10:36 GMT
FROM:    Takanori Sakamoto at Aoyama Gakuin U  <tsakamoto@phys.aoyama.ac.jp>

A.Y. Lien (GSFC/UMBC), S.D. Barthelmy (NASA/GSFC), D.M. Palmer (LANL),
T. Sakamoto (AGU), A. A. Breeveld (MSSL-UCL), A.P. Beardmore (U. Leicester),
D.N. Burrows (PSU), S. Campana (INAF-OAB), S.B. Cenko (NASA/GSFC),
G. Cusumano (INAF-IASF PA), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB),
V.D'Elia(ASDC), P.A. Evans (U. Leicester), N. Gehrels (NASA/GSFC),
P. Giommi (ASI), C. Gronwall (PSU), J. A. Kennea (PSU),
H.A. Krimm (CRESST/GSFC/USRA), N.P.M. Kuin (UCL-MSSL), D. Malesani (DARK/NBI),
F.E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB), B. Mingo (U. Leicester),
J.A. Nousek (PSU), S.R. Oates (Uni. of Warwick), P.T. O'Brien (U. Leicester),
J.P. Osborne (U. Leicester), C. Pagani (U. Leicester), K.L. Page (U.Leicester),
M. Perri (ASDC), J.L. Racusin (NASA/GSFC), B. Sbarufatti (INAF-OAB/PSU),
M.H. Siegel (PSU), G. Tagliaferri (INAF-OAB), E. Troja (NASA/GSFC/UMCP)
report on behalf of the Swift team:

We report the search results in the BAT data within T0 +/- 100 s of the
LIGO event G268556 (Shawhan et al. GCN Circ. 20364) , where T0 is the
LIGO trigger time (2017-01-04T10:11:58:599 UTC).

The BAT pointing position at T0 is
RA = 166.157 deg,
DEC = 38.204 deg,
ROLL = 81.247 deg.
The BAT Field of View (>0.1 partial coding) covers 48% of the integrated
LIGO localization probability.

There are no BAT event data in this time range (usually event data are only
collected for ~ 1000 s around the BAT trigger time). Also, no significant
detections (signal-to-noise ratio > 4 sigma) are found in the BAT raw light
curves with time bins of 64 ms, 1 s, and 1.6 s, respectively. Assuming an
on-axis (100% coded) short GRB with a typical spectrum in the BAT energy range
(i.e., a simple power-law model with a power-law index of -1.32; Lien & Sakamoto
et al. 2016), the 4-sigma upper limit in the 1-s binned light curve corresponds
to a flux upper limit (15-350 keV) of ~ 6.0 x 10^-8 erg/s/cm^2.

BAT retains decreased, but significant, sensitivity to rate increases for
gamma-ray events outside of its FOV. About 19% of the integrated LIGO localization
probability was outside of the BAT FOV but above the Earth's limb from Swift's
location, and the corresponding flux upper limits for this region are within roughly
an order of magnitude of those within the FOV.