TITLE:   GCN CIRCULAR
NUMBER:  27444
SUBJECT: GRB 200325A: Swift/BAT detection and probable arcminute localization of a short GRB from GUANO
DATE:    20/03/26 00:52:23 GMT
FROM:    Aaron Tohuvavohu at U Toronto  <aaron.tohu@gmail.com>

James DeLaunay (PSU), Aaron Tohuvavohu (U Toronto), and Jamie Kennea
(PSU) report:

Swift/BAT did not trigger on GRB 200325A.

The Fermi/GBM Flight-Position notice, distributed at T0+8 seconds,
from the Fermi/GBM detected GRB 200325A (GCN. 27434), as well as the
INTEGRAL SPI-ACS notice (Trig #8558) distributed at T0+44 seconds,
both triggered the Swift Mission Operations Center operated Gamma-ray
Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al.
2020, in prep). GRB 200325A was also detected by AGILE/MCAL (GCN.
27437) and AstroSat CZTI (GCN. 27438).

The GUANO is a fully autonomous, extremely low latency, spacecraft
commanding pipeline designed for targeted recovery of BAT event mode
data around the times of compelling astrophysical events to enable
more sensitive GRB searches.

Upon trigger by these notices, GUANO sent a command to the Swift Burst
Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from
[-50,+150] seconds around the time of GRB 200228A.

All the requested event mode data was delivered to the ground.

In a ground analysis of the data, using the normal BAT imaging
technique, we detect GRB 200228A with a SNR of 7.5.

With a more sophisticated maximum likelihood analysis (DeLaunay et
al.,  2020 in prep.) on the event-mode data we detect GRB 200325A more
confidently, with a square root of the test statistic, sqrt(TS), of
21.7. The sqrt(TS) behaves similarly to SNR.
The detected duration is ~1.1s.

The BAT ground-calculated position is
RA, Dec = 31.7203, -31.816 deg which is
   RA(J2000)  = 2h 6m 52.8s
   Dec(J2000) =  -31d 48’ 57.60”
with an uncertainty of 4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 8.2%.

This arcminute location is consistent with the localization region
distributed by the Fermi/GBM team (GCN. 27434), lying on the 75%
containment contour.
Due to the very low partial coding, we stress that this localization,
while significant, has some additional unquantified uncertainties
associated with it.

No XRT or UVOT follow-up will take place due to the source’s proximity
to the sun (1.5 hours).
We encourage follow-up from instruments capable of observing near the sun.

A live reporting of Swift/BAT event data recovered by GUANO can be found
 at: https://www.swift.psu.edu/guano/