TITLE: GCN CIRCULAR NUMBER: 36593 SUBJECT: Swift Trigger 1232465 is not a GRB DATE: 24/06/01 21:50:38 GMT FROM: David Palmer at LANL palmer@lanl.gov
J.D. Gropp (PSU), R. Gupta (NASA/GSFC), A. Y. Lien (U Tampa) and D. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift Observatory Team:
At 21:30:20 UT, the Swift Burst Alert Telescope (BAT) triggered on a rate increase and a marginal peak in the resulting image (trigger=1232465). Swift slewed immediately to the peak location. The BAT on-board calculated location is RA, Dec 108.731, -6.206 which is RA(J2000) = 07h 14m 55s Dec(J2000) = -06d 12' 20" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The available BAT light curve does not show any significant fluctuations above the noise level.
The XRT began observing the field at 21:31:59.9 UT, 99.7 seconds after the BAT trigger. No source was detected in 559 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 104 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. The typical 3-sigma upper limit has been about 19.6 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the BAT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the large, but uncertain, extinction expected.
Due to the marginal significance of the initial rate trigger (6.5 sigma in 0.032 s) and the BAT image (6.8 sigma), and the lack of an observed counterpart in the XRT and UVOT data, we believe that this is probably a statistical fluctuation and not a real astrophysical event.
Further analysis of the complete downlinked dataset will be used to conclusively rule out this event.
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