TITLE: GCN CIRCULAR NUMBER: 39794 SUBJECT: GRB 250321A: Swift detection of a burst DATE: 25/03/21 01:04:22 GMT FROM: David Palmer at LANL palmer@lanl.gov
R. Gupta (NASA GSFC), J. A. Kennea (PSU), N. J. Klingler (GSFC/UMBC/CRESSTII), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team:
At 00:42:38 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250321A (trigger=1297508). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 295.077, +21.041 which is RA(J2000) = 19h 40m 19s Dec(J2000) = +21d 02' 27" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). Only the first 8 seconds of the BAT light curve after the trigger is available due to a telemetry gap. This data shows a complex structure with a duration of at least 10 sec. The peak count rate was ~2500 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 00:44:43.60 UT, 125.6 seconds after the BAT trigger. No source was detected in the 2.5-s promptly available image. We are waiting for the full dataset to detect and localise the XRT counterpart.
Due to a telemetry gap, UVOT data are not available at this time.
Although XRT did not report an X-ray counterpart in the limited immediately transmitted data, the significance of the BAT image (>10 sigma), the shape of the BAT light curve, and the simultaneous detection by Fermi/GBM (trigger 764210564) give us confidence that this is an astrophysical Gamma Ray Burst.
Burst Advocate for this burst is R. Gupta (rahulbhu.c157 AT gmail.com). 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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