GCN Circular 40736

S. Dichiara (PSU), J. J. DeLaunay (PSU), R. Gupta (NASA GSFC) and
T. Sakamoto (AGU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 22:25:19.59 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 250615A (trigger=1324646). Swift slewed immediately to the burst.
The BAT on-board calculated location is RA, Dec 290.344, +4.672 which is 
   RA(J2000) = 19h 21m 23s
   Dec(J2000) = +04d 40’ 21"
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 55 sec.  The peak count rate 
was ~5000 counts/sec (15-350 keV), at ~1 sec after the trigger.

The XRT began observing the field at 22:26:46.4 UT, 86.9 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 290.38466, 4.68467
which is equivalent to:
   RA(J2000)  = 19h 21m 32.32s
   Dec(J2000) = +04d 41' 04.8"
with an uncertainty of 3.6 arcseconds (radius, 90% containment). This
location is 152 arcseconds from the BAT onboard position, within the
BAT error circle. This position may be improved as more data are
received; the latest position is available at
https://www.swift.ac.uk/sper. 

A power-law fit to a spectrum formed from promptly downlinked event
data does not constrain the column density. 

The initial flux in the 2.5 s image was 9.89e-10 erg cm^-2 s^-1 (0.2-10
keV).

UVOT took a finding chart exposure of 250 seconds with the U filter starting
152 seconds after the BAT trigger. No credible afterglow candidate has been
found in the initial data products. Results from the 2.7'x2.7' sub-image are
not available at this time. The 8'x8' region for the list of sources generated
on-board covers 100% of the XRT error circle. The list of sources is typically
complete to about 18.0 mag. No correction has been made for the large, but
uncertain, extinction expected.

Burst Advocate for this burst is S. Dichiara (sbd5667 AT 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/)