TITLE:   GCN CIRCULAR
NUMBER:  31501
SUBJECT: GRB 220117C: Swift/BAT-GUANO arcminute localization
DATE:    22/01/20 02:41:26 GMT
FROM:    Aaron Tohuvavohu at U Toronto  <aaron.tohu@gmail.com>

Gayathri Raman (PSU), James DeLaunay (UAlabama), Aaron Tohuvavohu (U
Toronto), Jamie A. Kennea (PSU), report:

Swift/BAT did not localize GRB 220117C onboard (T0:
2022-01-17T04:45:55 UTC, Fermi/GBM trigger #664087560).

The Fermi notice, distributed in near real-time, triggered the Swift
Mission Operations Center operated Gamma-ray Urgent Archiver for Novel
Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1).

Upon trigger by this notice, 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 the burst. All the requested
event mode data was delivered to the ground.

The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu,
arXiv:2111.01769), confidently detects the burst in a 8.192 s analysis
time bin with a sqrt(TS) of 19.5.
Estimated T90 in the detector is 8.55+/-0.07 s (10-350 keV).

An arcminute localization is found with DeltaLLHOut of 96.3 and a
DeltaLLHPeak of 58.7.
Using the conventional BAT imaging technique, we find an SNR of 6.1 at
the same location.

See Section 9.1 and Figure 20 in the NITRATES paper for brief
descriptions and interpretations of sqrt(TS), DeltaLLHPeak, and
DeltaLLHOut.

The BAT position is
RA, Dec = 286.457, +16.791 deg which is
   RA(J2000)  = 19h 05m 49.7s
   Dec(J2000) = +16d 47′ 27.6″
with an estimated uncertainty of 2 arcmin.

The position is consistent with the Fermi/GBM localization.

No XRT/UVOT followup will take place (GCN 31500).
We encourage followup from other facilities.

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.