TITLE:   GCN CIRCULAR
NUMBER:  29819
SUBJECT: GRB 210413B: Swift/BAT detection and probable localization of a short burst
DATE:    21/04/16 00:04:06 GMT
FROM:    Aaron Tohuvavohu at U Toronto  <aaron.tohu@gmail.com>

Swift/BAT did not successfully trigger on GRB 210413B (T0: 2021-04-13
23:46:52.45 UTC, Fermi/GBM TRIGGER 640050417).

The GUANO system is currently offline, thus no extended GUANO data is
available for this time, and so the sensitive GUANO MLL analysis
(DeLaunay et al. 2021, in prep) can not be run.

Swift/BAT triggered in real-time onboard in the rates domain (trigger
#1043009), but no strong source was found to be associated in the
onboard imaging. This 'failed trigger' resulted in 10s of BAT TTE data
being saved and sent to the ground.

The duration of the burst, as seen by BAT, is T90 = 1.088 s +/- 0.09 s.

In ground analysis of the available TTE data, we find a source using
typical imaging analysis, that is the likely location of the GRB, with
SNR 6 in the image domain.
The BAT position is
RA, Dec = 182.558 +55.965, which is:
    RA (J2000)     12h 10m 13.920s
    Dec (J2000)  +55d 57' 54.00"
with an estimated uncertainty of 3 arcminutes.

This location is consistent with the Fermi/GBM localization
distributed in the Final Position notice.

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