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GCN Circular 27289

LIGO/Virgo S200302c: no counterpart candidates in the Swift/BAT observations
2020-03-02T22:53:03Z (4 years ago)
Amy Lien at GSFC <>
T. Sakamoto (AGU), S. D. Barthelmy (NASA/GSFC),
A. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL)
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 (U. of Birmingham), 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 (U. 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 S200302c (LIGO/VIRGO Collaboration GCN Circ. 27278),
where T0 is the LVC trigger time (2020-03-02T01:58:11.519 UTC).

The center of the BAT field of view (FOV) at T0 is
RA = 10.655 deg,
DEC = 41.334 deg,
and the roll angle is 223.231 deg.
The BAT FOV (>10% partial coding) covers 24.48% of the integrated
LVC localization probability, and 24.02% 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.

Within T0 +/- 100 s, no significant astrophysical 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. The ~5.9 sigma detection
seen at ~T-17.8 s in the 64 ms light curve is likely due to cosmic ray

Assuming a 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 ~ 6.99 x 10^-8 erg/s/cm^2 for the 100% coded region
(i.e., for a burst with 0 deg from BAT boresight) and ~ 1.47 x 10^-6
erg/s/cm2 for the 10% coded region (~56 deg from BAT boresight).
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),
these flux upper limits corresponds to a distance of ~ 85.94 Mpc (100%
coded)and ~ 18.73 Mpc (10% coded).

Event data are available from T0-45.142 s to T0+44.9692 s via the GUANO
system (Tohuvavohu et al. 2020, in prep). No significant detections
(above our typical image threshold of ~ 6.5 to 7 sigma) are found in the
15-350 keV images created using intervals of the whole event data range.

BAT retains decreased, but significant, sensitivity to rate increases for
gamma-ray events outside of its FOV. About 52.88% 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
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