TITLE: GCN CIRCULAR NUMBER: 10784 SUBJECT: GRB 100522A: Swift detection of a burst DATE: 10/05/22 04:14:56 GMT FROM: David Palmer at LANL E. Troja (NASA/GSFC/ORAU), A. P. Beardmore (U Leicester), M. M. Chester (PSU), J. M. Gelbord (PSU), S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), C. Pagani (U Leicester), D. M. Palmer (LANL), R. L. C. Starling (U Leicester), T. N. Ukwatta (GSFC/GWU) and L. Vetere (PSU) report on behalf of the Swift Team: At 03:45:52 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 100522A (trigger=422783). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 6.983, +9.417 which is RA(J2000) = 00h 27m 56s Dec(J2000) = +09d 25' 03" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multi-peaked structure with a first pair of peaks near T0 with a duration of about 5 sec and a second fainter and softer pair of peaks near T+30 s. The peak count rate was ~15,000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 03:46:57.7 UT, 65.4 seconds after the BAT trigger. Using promptly downlinked data we find a bright, fading, uncatalogued X-ray source with an enhanced position: RA, Dec 6.9867, 9.4023 which is equivalent to: RA(J2000) = 00h 27m 56.82s Dec(J2000) = +09d 24' 08.1" with an uncertainty of 2.2 arcseconds (radius, 90% containment). This location is 54 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (3.98e+20 cm^-2, Kalberla et al. 2005), with an excess column of 2.7 (+2.46/-2.10) x 10^21 cm^-2 (90% confidence). The initial flux in the 2.5 s image was 2.40e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 73 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 100% of the XRT error circle. The 3-sigma upper limit at the XRT position is 18.5 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.06. Burst Advocate for this burst is E. Troja (eleonora.troja AT nasa.gov). 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.)