[vsnet-grb-info 27339] GRB 210209A: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29442
SUBJECT: GRB 210209A: Swift detection of a burst
DATE:    21/02/09 21:51:50 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

S. Laha (GSFC/UMBC/CRESST), S. D. Barthelmy (GSFC), J.D. Gropp (PSU),
J. A. Kennea (PSU), N. J. Klingler (PSU), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester) and D. M. Palmer (LANL) report on behalf of
the Neil Gehrels Swift Observatory Team:

At 21:39:44 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 210209A (trigger=1031636).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 328.096, +43.559 which is 
   RA(J2000) = 21h 52m 23s
   Dec(J2000) = +43d 33' 31"
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 110 sec.  The peak count rate
was ~1600 counts/sec (15-350 keV), at ~5 sec after the trigger. 

The XRT began observing the field at 21:41:41.0 UT, 116.5 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 328.12298, 43.55745 which
is equivalent to:
   RA(J2000)  = 21h 52m 29.52s
   Dec(J2000) = +43d 33' 26.8"
with an uncertainty of 3.5 arcseconds (radius, 90% containment). This
location is 70 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. No
spectrum from the promptly downlinked event data is yet available to
determine the column density. 

The initial flux in the 2.5 s image was 3.98e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 126 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 100% 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 expected extinction corresponding to E(B-V) of
0.285. 

Burst Advocate for this burst is S. Laha (sib.laha AT gmail.com). 
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/)