TITLE: GCN CIRCULAR NUMBER: 36931 SUBJECT: Swift Trigger 1244778 is not a GRB DATE: 24/07/25 02:56:29 GMT FROM: David Palmer at LANL <palmer@lanl.gov> K. L. Page (U Leicester), D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 02:37:36 UT, the Swift Burst Alert Telescope (BAT) triggered on a rate fluctuation at the 0.032 s timescale and found a low-significance peak in the resulting image (trigger=1244778). Swift slewed immediately to the location. The BAT on-board calculated location is RA, Dec 299.054, -64.667 which is RA(J2000) = 19h 56m 13s Dec(J2000) = -64d 40' 00" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve does not show any obvious peak above the noise level. The XRT began observing the field at 02:39:04.6 UT, 87.7 seconds after the BAT trigger. No source was detected in 674 s of promptly downlinked data. UVOT took a finding chart exposure of 250 seconds with the U filter starting 303 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 19.2 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 18.0 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.068. Due to the marginal signal in the BAT (6.7 sigma in rates, 6.7 sigma in the image) and the lack of an XRT or UVOT counterpart, we believe that this is merely a statistical fluctuation in the BAT image reconstruction and not an astrophysical event. This conclusion is expected to be confirmed when the full dataset is available on the ground. View this GCN Circular online at https://gcn.nasa.gov/circulars/36931. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...