LIGO/Virgo S191204r: Swift/BAT Counterpart Search

<somebody goes first>
S. D. Barthelmy (NASA/GSFC), A. Y. Lien (GSFC/UMBC), 
D. M. Palmer (LANL), 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-ASDC), 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 S191204r (LIGO/VIRGO Collaboration GCN Circ. XXXXX), 
where T0 is the LVC trigger time (2019-12-04T17:15:26.091 UTC).

The center of the BAT field of view (FOV) at T0 is
RA = 46.016 deg,
DEC = -16.004 deg,
and the roll angle is 201.965 deg.
The BAT FOV (>10% partial coding) covers 96.35% of the integrated
LVC localization probability, and 78.39% of the galaxy convolved 
probability (Evans et al. 2016). Note that 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.

[If there are significant detection, change the following paragraph accordingly]
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 ~ 2.08 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 ~ 49.83 Mpc.

[Description of event data analysis, if available]

BAT retains decreased, but significant, sensitivity to rate increases for
gamma-ray events outside of its FOV. About 3.65% 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/S191204r/web/source_public.html