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GCN Circular 28307

Subject
GRB 200829A: Swift detection of a burst with an optical afterglow
Date
2020-08-29T14:18:33Z (3 years ago)
From
Boris Sbarufatti at PSU <bxs60@psu.edu>
M. H. Siegel (PSU), J.D. Gropp (PSU), J. A. Kennea (PSU),
N. P. M. Kuin (UCL-MSSL), S. Laha (GSFC/UMBC/CRESST) and
B. Sbarufatti (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 13:59:34 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 200829A (trigger=993768).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 251.212, +72.335 which is 
   RA(J2000) = 16h 44m 51s
   Dec(J2000) = +72d 20' 07"
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 30 sec.  The peak count rate
was ~1335 counts/sec (15-350 keV), at ~6 sec after the trigger. 

The XRT began observing the field at 14:01:43.1 UT, 128.7 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 251.2096, 72.3273 which is equivalent to:
   RA(J2000)  = 16h 44m 50.30s
   Dec(J2000) = +72d 19' 38.3"
with an uncertainty of 4.7 arcseconds (radius, 90% containment). This
location is 27 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 2.5 s image was 9.30e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 138 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	16:44:49.05 = 251.20439
  DEC(J2000) = +72:19:45.3  =  72.32924
with a 90%-confidence error radius of about 0.61 arc sec. This position is 9.0
arc sec. from the center of the XRT error circle. The estimated magnitude is
14.28 with a 1-sigma error of about  0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.04. 

Burst Advocate for this burst is M. H. Siegel (siegel AT swift.psu.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/)
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