[vsnet-grb-info 22085] LIGO/Virgo S190425z: Swift/BAT Counterpart Search

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24184
SUBJECT: LIGO/Virgo S190425z: Swift/BAT Counterpart Search
DATE:    19/04/25 15:18:44 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien at nasa.gov>

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(ASDC), 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), 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), 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 S190425z (LIGO/VIRGO Collaboration GCN Circ. 24168),
where T0 is the LVC trigger time (2019-04-25T08:18:05.000 UTC).

The center of the BAT FOV at T0 is
RA = 123.263 deg,
DEC = 22.657 deg,
ROLL = 279.608 deg.
The BAT Field of View (>10% partial coding) covers 7.26% of the integrated
LVC localization probability,  and 5.31% 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 ~ 8.01 x 10^-8 erg/s/cm^2.

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 45.73% 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 of those
within the FOV.

The results of the BAT analysis are available at
https://swift.gsfc.nasa.gov/results/BATbursts/team_web/S190425z/web/source_20190425.html