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GCN Circular 7639

Subject
GRB 080426: Swift detection of a possibly short burst
Date
2008-04-26T13:49:12Z (16 years ago)
From
David Burrows at PSU/Swift <dxb15@psu.edu>
H. Ziaeepour (UCL-MSSL), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
D. N. Burrows (PSU), N. Gehrels (NASA/GSFC), C. Guidorzi (INAF-OAB),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
N. P. M. Kuin (MSSL), J. Mao (INAF-OAB),
C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC),
P. T. O'Brien (U Leicester), S. R. Oates (UCL-MSSL), C. Pagani (PSU),
D. M. Palmer (LANL), D. Perez (U Leicester),
R. L. C. Starling (U Leicester), G. Tagliaferri (INAF-OAB),
T. N. Ukwatta (GSFC/GWU) and P. A. Ward (MSSL-UCL) report on behalf
of the Swift Team:

At 13:23:22 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080426 (trigger=310219).  Swift slewed to the burst
after a brief delay due to Earth limb constraint. 
The BAT on-board calculated location is 
RA, Dec 26.574, +69.492 which is 
   RA(J2000) = 01h 46m 18s
   Dec(J2000) = +69d 29' 30"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single-peaked
structure with a duration of about 2 sec.  The peak count rate
was ~7500 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 13:27:05.2 UT, 222.5 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 26.49931, 69.46856
which is equivalent to:
   RA(J2000)  = 01h 45m 59.83s
   Dec(J2000) = +69d 28' 06.8"
with an uncertainty of 2.8 arcseconds (radius, 90% containment). This
location is 126 arcseconds from the BAT onboard position, within the
BAT error circle. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of
3.65e+21 cm^-2 (Kalberla et al. 2005), so we cannot constrain the
redshift at this time using the relation from Grupe et al. (2007). A
summary of the promptly downlinked data is given at
http://www.swift.ac.uk/sper/310219/. 

UVOT took a finding chart exposure of 100 seconds with the White  
(160-650 nm)filter starting 226 seconds after the BAT trigger. No  
afterglow candidate has  been found in the initial data products. The 
typical 3-sigma upper limit has been about 18.5 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 18mag. No correction has been made for the expected 
extinction corresponding to E(B-V) of 0.79. 

Burst Advocate for this burst is H. Ziaeepour (hz AT mssl.ucl.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/too.html.)
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