Difference: GCNCIRCULAR20772 (1 vs. 2)

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/NB= I), 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.Leicest= er), 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 1B$B!^=1B(B 100 s o f the LIGO event G275697 (LIGO/VIRGO Collaboration GCN Circ. 20763), where T0 is the LIGO trigger time (2017-02-27T18:57:31.375 UTC).

The BAT pointing position at T0 is

RA =3D 284.163 deg,
DEC =3D -37.915 deg,
ROLL =3D 78.846 deg.

The BAT Field of View (>10% partial coding) covers 8.28% of the integrated LIGO localization probability.

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, respec= tively. Assuming an on-axis (100% coded) short GRB with a typical spectrum in the B= AT energy range (i.e., a simple power-law model with a power-law index of -1.3= 2; Lien & Sakamoto et al. 2016), the 4-sigma upper limit in the 1-s binned lig= ht curve corresponds to a flux upper limit (15-350 keV) of ~ 6.8 x 10^-8 erg/s= /cm^2. Moreover, so far no event data are found within T0 =1B$B!^=1B(B 100 s.

BAT retains decreased, but significant, sensitivity to rate increases for gamma-ray events outside of its FOV. About 58.37% of the integrated LIGO localization probability was outside of the BAT FOV but above the Earth's l= imb from Swift's location, and the corresponding flux upper limits for this reg= ion are within roughly an order of magnitude of those within the FOV.

-- ThomasKupfer - 28 Feb 2017