TITLE: GCN CIRCULAR NUMBER: 31347 SUBJECT: GRB 220101A: Swift detection of a burst with a bright optical counterpart DATE: 22/01/01 05:32:40 GMT FROM: David Palmer at LANL palmer@lanl.gov

A. Tohuvavohu (U Toronto), J.D. Gropp (PSU), J. A. Kennea (PSU), A. Y. Lien (U Tampa), D. M. Palmer (LANL), T. M. Parsotan (GSFC/UMBC/CRESSTII), B. Sbarufatti (PSU) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team:

At 05:09:55 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 220101A (trigger=1091101). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 1.380, +31.753 which is RA(J2000) = 00h 05m 31s Dec(J2000) = +31d 45' 09" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT lightcurve shows a complex lightcurve extending to at least T+170 with a peak of 7000 counts/s (15-350 keV), at ~89 sec after the trigger.

The XRT began observing the field at 05:11:32.2 UT, 80.8 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 1.3561, 31.7702 which is equivalent to: RA(J2000) = 00h 05m 25.46s Dec(J2000) = +31d 46' 12.7" with an uncertainty of 4.7 arcseconds (radius, 90% containment). This location is 95 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.

The initial flux in the 2.5 s image was 1.30e-08 erg cm^-2 s^-1 (0.2-10 keV).

UVOT took a finding chart exposure of 150 seconds with the White filter starting 89 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 00:05:24.82 = 1.35340 DEC(J2000) = +31:46:08.5 = 31.76903 with a 90%-confidence error radius of about 0.61 arc sec. This position is 9.3 arc sec. from the center of the XRT error circle. The estimated magnitude is 14.60 with a 1-sigma error of about 0.14. No correction has been made for the expected extinction corresponding to E(B-V) of 0.056.

Burst Advocate for this burst is A. Tohuvavohu (aaron.tohu AT gmail.com). 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/)