TITLE:   GCN CIRCULAR
NUMBER:  28958
SUBJECT: GRB 201128A: Swift detection of a burst
DATE:    20/11/28 06:44:21 GMT
FROM:    David Palmer at LANL  <palmer@lanl.gov>

A. Y. Lien (GSFC/UMBC), E. Ambrosi (INAF-IASFPA),
A. D'Ai (INAF-IASFPA), V. D'Elia (SSDC), J.D. Gropp (PSU),
J. A. Kennea (PSU), N. J. Klingler (PSU), S. Laha (GSFC/UMBC/CRESST),
K. L. Page (U Leicester), D. M. Palmer (LANL), M. H. Siegel (PSU) and
M. Stamatikos (OSU/NASA/GSFC) report on behalf of the Neil Gehrels
Swift Observatory Team:

At 06:27:58 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 201128A (trigger=1009679).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 223.136, +26.678 which is 
   RA(J2000) = 14h 52m 33s
   Dec(J2000) = +26d 40' 41"
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 10 sec.  The peak count rate
was ~600 counts/sec (15-350 keV), at ~2 sec after the trigger. 

The XRT began observing the field at 06:30:04.8 UT, 126.6 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 223.1083, 26.6844 which
is equivalent to:
   RA(J2000)  = 14h 52m 26.00s
   Dec(J2000) = +26d 41' 03.8"
with an uncertainty of 2.6 arcseconds (radius, 90% containment). This
location is 92 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 consistent with the Galactic value of 3.53
x 10^20 cm^-2 (Willingale et al. 2013). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 130 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers none of
the XRT error circle. The 8'x8' region for the list of sources generated
on-board covers 100% of the XRT error circle. The list of sources is typically
complete to about 18 mag. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.03. 

Burst Advocate for this burst is A. Y. Lien (amy.y.lien 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/)