GCN Circular 43285

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/)