TITLE:   GCN CIRCULAR
NUMBER:  42197
SUBJECT: GRB 251011B: Swift detection of a burst
DATE:    25/10/11 07:29:21 GMT
FROM:    Antonino D'Ai' at INAF <antonino.dai@inaf.it>

A. D'Ai (INAF-IASFPA), E. Ambrosi (INAF-IASFPA),
V. D'Elia (SSDC & INAF-OAR), R. Gupta (NASA GSFC),
N. P. M. Kuin (UCL-MSSL), A. Melandri (INAF-OAR),
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 07:08:22.33 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 251011B (trigger=1403191).  Swift slewed immediately to the burst.
The BAT on-board calculated location is 
RA, Dec 13.287, -62.032 which is 
   RA(J2000) = 00h 53m 09s
   Dec(J2000) = -62d 01' 55"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty). The BAT light curve showed a complex structure
with a duration of about 150 seconds.  The peak count rate was ~3000
counts/sec (15-350 keV) at ~0 sec after the trigger.

The XRT began observing the field at 07:09:58.8 UT, 96.5 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 13.23523,
-62.03269 which is equivalent to:
   RA(J2000)  = 00h 52m 56.46s
   Dec(J2000) = -62d 01' 57.7"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 87 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 (1.68 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 4.5
(+3.47/-2.92) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 1.95e-09 erg cm^-2 s^-1 (0.2-10
keV).

UVOT data are unavailable at this time.

Burst Advocate for this burst is A. D'Ai (antonino.dai AT inaf.it).
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/)