[vsnet-grb-info 27294] GRB 210205A: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29397
SUBJECT: GRB 210205A: Swift detection of a burst
DATE:    21/02/05 11:27:17 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at milkyway.gsfc.nasa.gov>

S. Dichiara (NASA/GSFC/UMCP), E. Ambrosi (INAF-IASFPA),
S. D. Barthelmy (GSFC), V. D'Elia (SSDC), P. A. Evans (U Leicester),
J.D. Gropp (PSU), H. A. Krimm (NSF), N. P. M. Kuin (UCL-MSSL),
A. Y. Lien (GSFC/UMBC) and K. L. Page (U Leicester) report on behalf
of the Neil Gehrels Swift Observatory Team:

At 11:11:17 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 210205A (trigger=1030629).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 347.257, +56.312 which is 
   RA(J2000)  =  23h 09m 02s
   Dec(J2000) = +56d 18' 45"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a multi-peak
structure with a duration of about 35 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~2 sec after the trigger. 

The XRT began observing the field at 11:13:32.2 UT, 134.7 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 347.2214, 56.2943 which
is equivalent to:
   RA(J2000)  = 23h 08m 53.13s
   Dec(J2000) = +56d 17' 39.4"
with an uncertainty of 2.6 arcseconds (radius, 90% containment). This
location is 95 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 5.15
x 10^21 cm^-2 (Willingale et al. 2013). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 138 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 47% of
the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 
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 large, but uncertain, extinction expected. 

Burst Advocate for this burst is S. Dichiara (dichiara AT umd.edu). 
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/)