GCN Circular 20494
Subject
LIGO/Virgo G270580: Swift/BAT data search
Date
2017-01-21T11:15:23Z (8 years ago)
From
Takanori Sakamoto at Aoyama Gakuin U <tsakamoto@phys.aoyama.ac.jp>
S.D. Barthelmy (NASA/GSFC), A. Y. Lien (GSFC/UMBC), 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 G270580 (LIGO/VIRGO Collaboration GCN Circ. 20486),
where T0 is the LIGO trigger time (2017-01-20T12:31:00.350 UTC).
The BAT pointing position at T0 is
RA = 61.726 deg,
DEC = -71.914 deg,
ROLL = 229.416 deg.
The BAT Field of View (>0.1 partial coding) covers 17.98% of the integrated
LIGO localization probability.
The closest event data covers the time range from T0-138.839 to T0-0.747.
No sources with signal-to-noise ratio > 6 sigma are found in the event data.
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 ~ 8.3 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 18.42% 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.