GCN Circular 25843

D. M. Palmer (LANL), S. D. Barthelmy (NASA/GSFC),
A. Y. Lien (GSFC/UMBC), T. Sakamoto (AGU),
A. P. Beardmore (U. Leicester), M. G. Bernardini (INAF-OAB),
A. A. Breeveld (MSSL-UCL), 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 (ASI-SSDC), S. Emery (UCL-MSSL),
P. A. Evans (U. Leicester), P. Giommi (ASI), C. Gronwall (PSU),
D. Hartmann (Clemson U.), J. A. Kennea (PSU),
N. Klingler (PSU), H. A. Krimm (NSF),
N. P. M. Kuin (UCL-MSSL), F. E. Marshall (NASA/GSFC),
A. Melandri (INAF-OAB), 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. J. Page (UCL-MSSL), M. Perri (ASDC),
J. L. Racusin (NASA/GSFC), B. Sbarufatti (INAF-OAB/PSU),
M. H. Siegel (PSU), G. Tagliaferri (INAF-OAB), A. Tohuvavohu (Toronto),
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
LVC event S190924h (LIGO/VIRGO Collaboration GCN Circ. 25829
Not found
 
 
),
where T0 is the LVC trigger time (2019-09-24T02:18:46.846 UTC).

The center of the BAT field of view (FOV) at T0 is
RA = 159.491 deg,
DEC = 44.352 deg,
and the roll angle is 157.702 deg.
The BAT FOV (>10% partial coding) covers 70.30% of the integrated
LVC localization probability, and 71.67% of the galaxy convolved
probability (Evans et al. 2016). Note that Swift was slewing
from ~T0-10 s to ~T0+160 s. Also, the sensitivity in the BAT FOV
changes with the partial coding fraction. Please see the BAT FOV
figure in the summary page (link below) for the specific location of
the LVC region relative to the BAT FOV.

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. 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 ~ 2.57 x 10^-7 erg/s/cm^2.
Assuming a luminosity of ~ 2 x 10^47 erg/s (similar to GW170817)
and an average Epeak of ~ 400 keV for short GRBs (Bhat et al. 2016),
this flux upper limit corresponds to a distance of ~ 44.79 Mpc.

No event data are available at this time.

BAT retains decreased, but significant, sensitivity to rate increases for
gamma-ray events outside of its FOV. About 29.70% of the integrated LVC
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 higher than those
within the FOV.

The results of the BAT analysis are available at
https://swift.gsfc.nasa.gov/results/BATbursts/team_web/S190924h/web/source_public.html