GCN Circular 45896

S. B. Cenko (GSFC), S. D. Barthelmy (GSFC), S. Dichiara (PSU),
R. Gupta (NASA GSFC), N. P. M. Kuin (UCL-MSSL), A. Y. Lien (U Tampa),
M. J. Moss (GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL), 
and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team:

At 13:46:41 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 261011A (trigger=1516664).  Swift slewed immediately to the burst.
The BAT on-board calculated location is 
RA, Dec 21.925, -21.529 which is 
   RA(J2000) = 01h 27m 42s
   Dec(J2000) = -21d 31' 42"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a broad soft pulse 
from T0 to T0+130 sec and a shoulder extending out to T0+260 sec for a total 
duration of about 260 sec.  The peak count rate was ~8000 counts/sec 
(15-350 keV), at ~95 sec after the trigger.

The XRT began observing the field at 13:51:57.1 UT, 315.8 seconds after
the BAT trigger. No source was detected in the 2.5-s promptly available
image. We are waiting for the full dataset to detect and localise the
XRT counterpart.

UVOT took a finding chart exposure of nominal 150.000 seconds with the White
filter starting 321 seconds after the BAT trigger. There is a candidate
afterglow in the list of sources generated on-board at
  RA(J2000)  =	01:27:35.39 =  21.89746
  DEC(J2000) = -21:33:37.2  = -21.56032
with a 90%-confidence error radius of about 1.10 arc sec. This position is
145.7 arc sec. from the center of the BAT error circle. The estimated magnitude
is 17.78. No correction has been made for extinction.

The BAT lightcurve is very unusual in that it combines a 260 second long
low energy emission mostly below 50 keV, with a ~5 second short peak
structure around T+95 seconds visible at all energies up the to 100-350 keV band.

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/)