TITLE: GCN CIRCULAR NUMBER: 43285 SUBJECT: GRB 260101A: Swift detection of a burst with an optical counterpart DATE: 26/01/01 01:13:39 GMT FROM: K.L. Page at U Leicester <klp5@leicester.ac.uk> S. B. Cenko (GSFC), J. J. DeLaunay (PSU), S. Dichiara (PSU), R. Gupta (NASA GSFC), N. P. M. Kuin (UCL-MSSL), A. Y. Lien (U Tampa), K. L. Page (U Leicester) and T. M. Parsotan (GSFC) report on behalf of the Neil Gehrels Swift Observatory Team: At 00:56:30 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 260101A (trigger=1429608). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 86.465, +63.568 which is RA(J2000) = 05h 45m 51s Dec(J2000) = +63d 34' 06" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multi-peaked structure with a duration of about 40 sec. The peak count rate was ~7000 counts/sec (15-350 keV), at ~25 sec after the trigger. The XRT began observing the field at 00:57:54.9 UT, 84.7 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 86.42741, 63.59172 which is equivalent to: RA(J2000) = 05h 45m 42.58s Dec(J2000) = +63d 35' 30.2" with an uncertainty of 3.5 arcseconds (radius, 90% containment). This location is 104 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 https://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 (1.60 x 10^21 cm^-2, Willingale et al. 2013), with an excess column of 3.3 (+3.30/-2.79) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 250 seconds with the U filter starting 144 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 05:45:42.94 = 86.42890 DEC(J2000) = +63:35:32.1 = 63.59225 with a 90%-confidence error radius of about 0.61 arc sec. This position is 4.5 arc sec. from the center of the XRT error circle. The estimated magnitude is 16.03 with a 1-sigma error of about 0.14. No correction has been made for the expected extinction corresponding to E(B-V) of 0.179. Burst Advocate for this burst is S. B. Cenko (brad.cenko 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/) View this GCN Circular online at https://gcn.nasa.gov/circulars/43285. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...