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GCN Circular 30677

Subject
GRB 210822A: Swift detection of a burst with an optical afterglow
Date
2021-08-22T09:52:13Z (3 years ago)
From
Kim Page at U.of Leicester <klp5@leicester.ac.uk>
K. L. Page (U Leicester), J.D. Gropp (PSU), N. P. M. Kuin (UCL-MSSL)
and A. Y. Lien (U Tampa) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 09:18:18 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 210822A (trigger=1069788).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 304.476, +5.265 which is 
   RA(J2000) = 20h 17m 54s
   Dec(J2000) = +05d 15' 54"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of about 30 sec.  The peak count rate
was ~38000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 09:19:32.7 UT, 74.6 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 304.4377, 5.2786 which is equivalent to:
   RA(J2000)  = 20h 17m 45.05s
   Dec(J2000) = +05d 16' 43.0"
with an uncertainty of 11.9 arcseconds (radius, 90% containment). This
location is 145 arcseconds from the BAT onboard position, within the
BAT error circle. No event data are yet available to determine the
column density using X-ray spectroscopy. 

The initial flux in the 0.1 s image was 1.25e-08 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 250 seconds with the U filter  
starting 297 seconds after the BAT trigger. An afterglow   candidate
has been found in the initial data products with a magnitude 
 of u = 13.81 +/- 0.03. No correction  has been made for the expected 
extinction corresponding to E(B-V) of  0.162.   The preliminary UVOT 
position is RA=304.43748, Dec = 5.28337 (J2000),  which is equivalent 
to:   
   RA = 20h 17m 45.0s,  
   Dec = +05d 17m 00.1s (J2000)    with an  uncertainty of about an
arcsecond. 

Burst Advocate for this burst is K. L. Page (klp5 AT leicester.ac.uk). 
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/)
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