TITLE: GCN CIRCULAR NUMBER: 40736 SUBJECT: GRB 250615A: Swift detection of a burst DATE: 25/06/15 22:44:24 GMT FROM: Simone Dichiara at Pennsylvania State University sbd5667@psu.edu
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 40â 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/)
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