TITLE:   GCN CIRCULAR
NUMBER:  21436
SUBJECT: LIGO/Virgo G296853: Swift/BAT data search
DATE:    17/08/09 16:34:28 GMT
FROM:    Amy Lien at GSFC/Swift  <amy.y.lien@nasa.gov>

D.M. Palmer (LANL), S.D. Barthelmy (NASA/GSFC), A. Y. Lien (GSFC/UMBC),
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), S. Emery (UCL-MSSL), P.A. Evans (U. Leicester), 
P. Giommi (ASI), C. Gronwall (PSU), J. A. Kennea (PSU), 
H.A. Krimm (CRESST/GSFC/USRA), N.P.M. Kuin (UCL-MSSL), 
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 G296853 (LIGO/VIRGO Collaboration GCN Circ. 21431), 
where T0 is the LIGO trigger time (2017-08-09T08:28:21.747 UTC).

The center of the BAT FOV at T0 is
RA = 305.082 deg,
DEC = 43.799 deg,
ROLL = 340.755 deg.
At T0, the BAT Field of View (>10% partial coding) covers 0.01% of the integrated
LIGO localization probability. That is, there is no overlap between the BAT 
field of view and the LIGO probability region at T0.

Within T0 +/- 100 s, no significant detections (signal-to-noise ratio >~ 5 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 5-sigma upper limit in the 1-s binned light 
curve corresponds to a flux upper limit (15-350 keV) of ~ 1.38 x 10^-7 erg/s/cm^2.

BAT retains decreased, but significant, sensitivity to rate increases for
gamma-ray events outside of its FOV. About 99.88% 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.