GRB 250612A

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/)

H. A. Krimm (NSF), S. D. Barthelmy (GSFC),
R. Gupta (GSFC), S. Laha (GSFC/UMBC),
A. Y. Lien (U Tampa), C. B. Markwardt (GSFC),
M. J. Moss (GSFC), D. M. Palmer (LANL),
T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC),
T. Sakamoto (AGU), M. H. Siegel (PSU)
(i.e. the Swift-BAT team):
 
Using the data set from T-240 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 250612A (trigger #1323295) (Siegel, et al., GCN Circ. 40694
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 ).  
The BAT ground-calculated position is
RA, Dec = 250.873, -38.948 deg which is 
   RA(J2000)  =  16h 43m 29.6s 
   Dec(J2000) = -38d 56' 53.9" 
with an uncertainty of 4.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 64%.
 
The BAT mask-weighted light curve showed a complex structure with a duration of about 300 sec. 
T90 (15-350 keV) is 274.17 +- 66.54 sec (estimated error including systematics).
 
The time-averaged spectrum from T-0.58 to T+291.52 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.55 +- 0.43.  The fluence in the 15-150 keV band is 1.0 +- 0.2 x 10^-06 erg/cm2.
The 1-sec peak photon flux measured from T+0.62 sec in the 15-150 keV band
is 0.9 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level. 

Given the BAT detection at a Galactic latitude of 4.6 deg and the absence of a detected X-ray afterglow in XRT observations ~ 17 hours post-trigger, a Galactic origin of this source remains plausible. If confirmed as a new Galactic transient, it would be designated Swift J1643.6−3854.

The results of the batgrbproduct analysis are available at
https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1323295