TITLE: GCN CIRCULAR NUMBER: 42290 SUBJECT: Swift Trigger 1404295: possible GRB 251015A DATE: 25/10/15 14:44:43 GMT FROM: K.L. Page at U Leicester klp5@leicester.ac.uk
N. J. Klingler (GSFC/UMBC/CRESSTII), R. Brivio (INAF-OAB), S. Dichiara (PSU), M. Ferro (INAF-OAB), R. Gupta (NASA GSFC), N. P. M. Kuin (UCL-MSSL), A. Mei (INAF-OAB), K. L. Page (U Leicester), D. M. Palmer (LANL), T. Sbarrato (INAF-OAB) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team:
At 14:17:23 UT, the Swift Burst Alert Telescope (BAT) triggered and located a possible GRB 251015A (trigger=1404295). Swift slewed immediately to the location. The BAT on-board calculated location is RA, Dec 245.007, -54.853 which is RA(J2000) = 16h 20m 02s Dec(J2000) = -54d 51' 10" 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 10 sec. The peak count rate was ~800 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 14:19:31.3 UT, 127.6 seconds after the BAT trigger. No source was detected in 877 s of promptly downlinked data. We are waiting for the full dataset to detect and localise the XRT counterpart.
UVOT took a finding chart exposure of 150 seconds with the White filter starting 870 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 25% of the BAT error circle. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the sub-image. The 8'x8' region for the list of sources generated on-board covers 0.00% of the BAT error circle. No correction has been made for the large, but uncertain, extinction expected.
Due to the marginal detection in the BAT image (6.53 sigma) and the lack of an XRT counterpart, we believe that this is most likely to be a noise fluctuation, but might be a GRB. Analysis of the complete downlinked dataset will be required to determine the reality of this event.
Burst Advocate for this burst is N. J. Klingler (noelklin AT umbc.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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