TITLE:   GCN CIRCULAR
NUMBER:  40694
SUBJECT: GRB 250612A: Swift detection of a burst or new Galactic transient Swift J1643.6-3854
DATE:    25/06/12 01:27:51 GMT
FROM:    James DeLaunay at PSU <jjd330@psu.edu>

M. H. Siegel (PSU), J. J. DeLaunay (PSU), R. Gupta (NASA GSFC) and
M. A. Williams (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 01:02:05.82 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 250612A (trigger=1323295). The BAT on-board calculated location is RA, Dec 250.903, -38.902 which is 
   RA(J2000) = 16h 43m 37s
   Dec(J2000) = -38d 54’ 06"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of about 5 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~1 sec after the trigger.

Due to a Moon observing constraint, Swift cannot slew to the BAT
position until 11:59 UT on 2025 June 12. There will thus be no XRT or
UVOT data for this trigger before this time.

Given the location of the BAT detection at a Galactic latitude of 4.6 deg and no confirmation of a fading afterglow due to observing constraints, we cannot rule out a Galactic origin. 
If this is a new Galactic transient we would name it Swift J1643.6-3854.

Burst Advocate for this burst is M. H. Siegel (siegel AT swift.psu.edu).
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/)