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GCN Circular 11047

Subject
GRB 100805A: Swift detection of a burst with an optical counterpart
Date
2010-08-05T04:27:27Z (14 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
E. A. Hoversten (PSU), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), J. M. Gelbord (PSU), C. Gronwall (PSU),
S. T. Holland (CRESST/USRA/GSFC), D. M. Palmer (LANL),
M. H. Siegel (PSU), M. C. Stroh (PSU) and T. N. Ukwatta (GSFC/GWU)
report on behalf of the Swift Team:

At 04:12:42 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 100805A (trigger=430957).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 299.874, +52.614 which is 
   RA(J2000) = 19h 59m 30s
   Dec(J2000) = +52d 36' 52"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a peak with a
duration of about 20 sec.  The peak count rate
was ~600 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 04:14:48.7 UT, 126.4 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source located at RA, Dec 299.87559, 52.62758 which
is equivalent to:
   RA(J2000)  = 19h 59m 30.14s
   Dec(J2000) = +52d 37' 39.3"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 47 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 http://www.swift.ac.uk/sper. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of
1.69e+21 cm^-2 (Kalberla et al. 2005). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 129 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	19:59:30.52 = 299.87716
  DEC(J2000) = +52:37:40.3  = 52.62787
with a 90%-confidence error radius of about 0.62 arc sec. This position is 3.6
arc sec. from the center of the XRT error circle. The estimated magnitude is
18.00 with a 1-sigma error of about 0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.19. 

Burst Advocate for this burst is E. A. Hoversten (hoversten AT astro.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/too.html.)
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