TITLE:   GCN CIRCULAR
NUMBER:  27259
SUBJECT: GRB 200228A: Swift/BAT detection and arcminute localization from GUANO
DATE:    20/02/28 14:53:21 GMT
FROM:    Aaron Tohuvavohu at U Toronto  <aaron.tohu@gmail.com>

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

Swift/BAT did not trigger on GRB 200228A, likely due to a slew.

The Fermi/GBM Flight-Position notice, distributed at T0+23 seconds,
from the Fermi/GBM detected GRB 200228A (GCN. 27247) triggered the
Swift Mission Operations Center operated Gamma-ray Urgent Archiver for
Novel Opportunities (GUANO; Tohuvavohu et al. 2020, in prep).

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 the Fermi 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 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 40.

The BAT ground-calculated position is
RA, Dec = 333.8928, -42.9443 deg which is
   RA(J2000)  = 333d 53’ 34.08”
   Dec(J2000) =  -42d 56' 39.48"
with an uncertainty of 3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 34%.

This arcminute location is consistent with the localization region
distributed by the Fermi/GBM team (GCN. 27247).

No XRT or UVOT follow-up will take place due to the source’s proximity
to the sun (0.5 hours).
We encourage follow-up from instruments capable of observing near the sun.