[vsnet-grb-info 22867] LIGO/Virgo S190701ah: No counterpart candidates in the Swift/BAT Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24966
SUBJECT: LIGO/Virgo S190701ah: No counterpart candidates in the Swift/BAT Observations
DATE:    19/07/02 12:59:23 GMT
FROM:    Takanori Sakamoto at AGU  <tsakamoto at phys.aoyama.ac.jp>

T. Sakamoto (AGU), S. D. Barthelmy (NASA/GSFC),
A. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL),
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 (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), 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 (PSU),
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 S190701ah (LIGO/VIRGO Collaboration GCN Circ. 24950),
where T0 is the LVC trigger time (2019-07-01T20:33:06.577 UTC).

The center of the BAT FOV at T0 is
RA = 10.445 deg,
DEC = 41.252 deg,
ROLL = 64.992 deg.
The BAT Field of View (>10% partial coding) covers 87.22% of the integrated
LVC localization probability, and 87.58% of the galaxy convolved
probability (Evans et al. 2016).

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 ~ 8.11 x 10^-8 erg/s/cm^2.

Event data are available from T0-100.77 to T0+99.42. No significant
detections are found in the 15-350 keV images made using between
T0-2.0 s and T0+8.0 s and whole event data duration.

BAT retains decreased, but significant, sensitivity to rate increases for
gamma-ray events outside of its FOV. About 12.78% 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/S190701ah/web/source.html