TITLE: GCN CIRCULAR NUMBER: 12228 SUBJECT: GRB 110801A: Swift detection of a burst with an optical counterpart DATE: 11/08/01 20:01:04 GMT FROM: Scott Barthelmy at NASA/GSFC M. De Pasquale (UCL-MSSL), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester), D. N. Burrows (PSU), J. R. Cummings (NASA/UMBC), P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC), S. T. Holland (CRESST/USRA/GSFC), E. A. Hoversten (PSU), J. A. Kennea (PSU), A. Melandri (INAF-OAB), C. J. Mountford (U Leicester), K. L. Page (U Leicester), D. M. Palmer (LANL), T. Sakamoto (NASA/UMBC), B. Sbarufatti (INAF-OAB/IASFPA), M. H. Siegel (PSU), E. Sonbas (GSFC/USRA/Adiyaman Univ.), C. A. Swenson (PSU), E. Troja (NASA/GSFC/ORAU) and T. N. Ukwatta (MSU) report on behalf of the Swift Team: At 19:49:42 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 110801A (trigger=458521). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 89.285, +80.988 which is RA(J2000) = 05h 57m 08s Dec(J2000) = +80d 59' 18" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a few weak peaks with a duration of about 70 sec. The peak count rate was ~700 counts/sec (15-350 keV), at ~1 sec after the trigger. The XRT began observing the field at 19:51:21.9 UT, 98.9 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 89.4307, +80.9548 which is equivalent to: RA(J2000) = 05h 57m 43.36s Dec(J2000) = +80d 57' 17.2" with an uncertainty of 4.9 arcseconds (radius, 90% containment). This location is 146 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy. UVOT took a finding chart exposure of 150 seconds with the White filter starting 108 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 05:57:44.73 = 89.43637 DEC(J2000) = +80:57:21.6 = 80.95600 with a 90%-confidence error radius of about 0.62 arc sec. This position is 5.4 arc sec. from the center of the XRT error circle. The estimated magnitude is 18.03 with a 1-sigma error of about 0.14. No correction has been made for the expected extinction corresponding to E(B-V) of 0.08. Burst Advocate for this burst is M. De Pasquale (mdp AT mssl.ucl.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.)