TITLE:   GCN CIRCULAR
NUMBER:  28237
SUBJECT: GRB 200809B: Swift/BAT-GUANO detection and arcminute localization
DATE:    20/08/09 18:57:54 GMT
FROM:    Aaron Tohuvavohu at U Toronto  <aaron.tohu@gmail.com>

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

Swift/BAT did not trigger on GRB 200809B (T0: 2020-08-09 15:41:27 UTC,
Fermi/GBM Team GCN 28236).

The Fermi/GBM notice, distributed at T0+7 seconds triggered the Swift
Mission Operations Center operated Gamma-ray Urgent Archiver for Novel
Opportunities (GUANO; Tohuvavohu et al. 2020, arXiv: 2005.01751).

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.

Using the normal BAT imaging technique, we find the location of the
GRB with an SNR of 10.4.

The BAT ground-calculated position is
RA, Dec = 15.9406, -73.8459 deg which is
   RA(J2000)  = 01h 3m 45.7s
   Dec(J2000) =  -73d 50’ 45.24”
with an uncertainty of 4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 28.9%.

This position is consistent with the Fermi GBM localization (GCN 28236).

XRT and UVOT follow-up has been triggered. Results of follow-up
observations will be reported in future circulars.

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.

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