GCN Circular 38354

C. Salvaggio (INAF-OAB), R. Brivio (INAF-OAB), S. Dichiara (PSU),
M. Ferro (INAF-OAB), R. Gupta (NASA GSFC), A. Y. Lien (U Tampa),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
A. Tohuvavohu (Caltech) and M. A. Williams (PSU) report on behalf of
the Neil Gehrels Swift Observatory Team:

At 21:43:16 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 241127A (trigger=1270788).  Swift slewed immediately to the burst.
The BAT on-board calculated location is 
RA, Dec 327.922, -56.685 which is 
   RA(J2000) = 21h 51m 41s
   Dec(J2000) = -56d 41' 06"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single-peaked
structure with a duration of about 10 sec.  The peak count rate
was ~2000 counts/sec (15-350 keV), at ~0 sec after the trigger.

The XRT began observing the field at 21:44:22.8 UT, 66.6 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 327.88355, -56.66459 which
is equivalent to:
   RA(J2000)  = 21h 51m 32.05s
   Dec(J2000) = -56d 39' 52.5"
with an uncertainty of 4.0 arcseconds (radius, 90% containment). This
location is 105 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.  We cannot determine whether the source
is fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (2.68 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 6.1
(+6.36/-4.83) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 2.12e-09 erg cm^-2 s^-1 (0.2-10
keV).

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 484 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	21:51:32.32 = 327.88467
  DEC(J2000) = -56:39:55.1  = -56.66531
with a 90%-confidence error radius of about 0.61 arc sec. This position is 2.1
arc sec. from the center of the XRT error circle. The estimated magnitude is
17.14 with a 1-sigma error of about  0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.034.

Burst Advocate for this burst is C. Salvaggio (chiara.salvaggio 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/)