GCN Circular 7473

D. Grupe (PSU), D. N. Burrows (PSU), M. M. Chester (PSU),
N. Gehrels (NASA/GSFC), S. Immler (CRESST/GSFC/UMD),
J. A. Kennea (PSU), C. B. Markwardt (CRESST/GSFC/UMD),
D. M. Palmer (LANL), A. M. Parsons (GSFC), J. L. Racusin (PSU),
M. Stamatikos (NASA/ORAU), T. N. Ukwatta (GSFC/GWU),
D. E. Vanden Berk (PSU) and L. Vetere (PSU) report on behalf of the
Swift Team:

At 04:37:38 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080320 (trigger=306858).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 177.780, +57.144 which is 
   RA(J2000) = 11h 51m 07s
   Dec(J2000) = +57d 08' 38"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a FRED
structure with a duration of about 25 sec.  The peak count rate
was ~1200 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 04:40:29.4 UT, 171.0 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 177.73502,
57.15776 which is equivalent to:
   RA(J2000)  = 11h 50m 56.41s
   Dec(J2000) = +57d 09' 27.9"
with an uncertainty of 2.5 arcseconds (radius, 90% containment). This
location is 100 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
1.35e+20 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/306858/. 

UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 177 seconds after the BAT trigger. No afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers 25% of
the BAT error circle but does not overlap the XRT error circle. 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
BAT 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
0.01. 

Burst Advocate for this burst is D. Grupe (grupe 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.)