TITLE: GCN CIRCULAR NUMBER: 10708 SUBJECT: Trigger 421072: Possible Swift detection of a GRB or transient DATE: 10/05/04 07:56:22 GMT FROM: David Palmer at LANL C. Pagani (U Leicester), A. P. Beardmore (U Leicester), S. Campana (INAF-OAB), P. A. Evans (U Leicester), C. Guidorzi (U Ferrara), O. M. Littlejohns (U Leicester), C. B. Markwardt (CRESST/GSFC/UMD), P. T. O'Brien (U Leicester), K. L. Page (U Leicester), D. M. Palmer (LANL), A. Rowlinson (U Leicester), M. Stamatikos (OSU/NASA/GSFC), M. A. Stark (PSU), R. L. C. Starling (U Leicester) and G. Tagliaferri (INAF-OAB) report on behalf of the Swift Team: At 07:28:34 UT, the Swift Burst Alert Telescope (BAT) located trigger 421072. Swift slewed immediately to the location. The BAT on-board calculated location is RA, Dec 98.246, +9.165 which is RA(J2000) = 06h 32m 59s Dec(J2000) = +09d 09' 55" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). Because the BAT trigger is based on a 64 s image in the 15-50 keV band, there is nothing obvious in the light curve, which is typical. In ground processing, the excess has a significance of 6.4 sigma. The XRT began observing the field at 07:30:31.7 UT, 117.5 seconds after the BAT trigger. No source was detected in the promptly available XRT 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 121 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. Data from the list of sources generated on-board are not available at this time. No correction has been made for the large, but uncertain extinction expected. Due to the low significance (6.4 sigma) of this source in the ground reprocessing of the BAT image, and the lack of confirmation by XRT and UVOT, we cannot confirm that this is an astrophysical source. Furthermore its proximity to the Galactic plane (7 arcmin) would suggest the possibility of it being a Galactic transient if it were real. Therefore further determination of the reality and nature of this source will require analysis of the Malindi data. Burst Advocate for this burst is C. Pagani (cp232 AT star.le.ac.uk). 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/too.html.)