[vsnet-grb-info 27369] GRB 210211A: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29472
SUBJECT: GRB 210211A: Swift detection of a burst
DATE:    21/02/11 09:00:56 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at star.le.ac.uk>

E. Troja (NASA/GSFC/UMCP), P. A. Evans (U Leicester),
H. A. Krimm (NSF), K. L. Page (U Leicester), B. Sbarufatti (PSU) and
M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 08:43:18 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 210211A (trigger=1032024).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 269.433, -46.299 which is 
   RA(J2000) = 17h 57m 44s
   Dec(J2000) = -46d 17' 57"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a double-peaked
structure with a duration of about 10 sec.  The peak count rate
was ~2500 counts/sec (15-350 keV), at ~4 sec after the trigger. 

The XRT began observing the field at 08:44:32.2 UT, 73.9 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 269.4374, -46.2660
which is equivalent to:
   RA(J2000)  = 17h 57m 44.99s
   Dec(J2000) = -46d 15' 57.7"
with an uncertainty of 3.4 arcseconds (radius, 90% containment). This
location is 119 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 (1.24 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 8.7
(+9.04/-6.57) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 77 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. Because of the density of
catalogued stars, further analysis is required to report an upper limit for any
afterglow in the region. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.126. 

Burst Advocate for this burst is E. Troja (eleonora.troja 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/)