TITLE: GCN CIRCULAR NUMBER: 14025 SUBJECT: GRB 121201A: a GRB with an optical counterpart DATE: 12/12/01 12:47:59 GMT FROM: David Palmer at LANL V. N. Yershov (UCL-MSSL), D. N. Burrows (PSU), N. P. M. Kuin (UCL-MSSL), F. E. Marshall (NASA/GSFC), S. R. Oates (UCL-MSSL), C. Pagani (U Leicester), K. L. Page (U Leicester), D. M. Palmer (LANL), M. H. Siegel (PSU) and T. N. Ukwatta (MSU) report on behalf of the Swift Team: At 12:25:42 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 121201A (trigger=540178). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 13.488, -42.952 which is RA(J2000) = 00h 53m 57s Dec(J2000) = -42d 57' 06" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve is incomplete at this time due to a telemetry drop out, lacking most of the time period covered by this image trigger. Activity is visible starting at T-10s, but this is coincident with a pre-planned slew. The XRT began observing the field at 12:27:37.1 UT, 115.1 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source with an enhanced position: RA, Dec 13.4676, -42.9432 which is equivalent to: RA(J2000) = 00h 53m 52.22s Dec(J2000) = -42d 56' 35.6" with an uncertainty of 2.1 arcseconds (radius, 90% containment). This location is 62 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 (1.99 x 10^20 cm^-2, Kalberla et al. 2005), with an excess column of 1.9 (+1.03/-0.96) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 119 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 00:53:52.17 = 13.46736 DEC(J2000) = -42:56:34.4 = -42.94290 with a 90%-confidence error radius of about 0.66 arc sec. This position is 3.4 arc sec. from the center of the XRT error circle. The estimated magnitude is 19.71 with a 1-sigma error of about 0.16. No correction has been made for the expected extinction corresponding to E(B-V) of 0.01. Burst Advocate for this burst is V. N. Yershov (vny 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.)