GCN Circular 7453

P. J. Brown (PSU), S. D. Barthelmy (GSFC), D. N. Burrows (PSU),
M. M. Chester (PSU), N. Gehrels (NASA/GSFC), O. Godet (U Leicester),
S. T. Holland (CRESST/USRA/GSFC), S. Immler (CRESST/GSFC/UMD),
J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA),
P. T. O'Brien (U Leicester), J. P. Osborne (U Leicester),
C. Pagani (PSU), K. L. Page (U Leicester), D. M. Palmer (LANL),
M. Perri (ASDC), J. L. Racusin (PSU), M. Stamatikos (NASA/ORAU),
R. L. C. Starling (U Leicester), E. Troja (U Leicester/INAF-IASFPA)
and T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team:

At 17:05:09 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080319D (trigger=306793).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 99.480, +23.933 which is 
   RA(J2000) = 06h 37m 55s
   Dec(J2000) = +23d 56' 01"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is usual with an image trigger, the prompt light 
curve does not not show any clear structure.  We will be able to tell more with 
the full data set. 

The XRT began observing the field at 17:07:36.9 UT, 147.5 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued, 
variable X-ray source with an enhanced position: RA, Dec 99.47270, 23.94306
which is equivalent to:
   RA(J2000)  = 06h 37m 53.45s
   Dec(J2000) = +23d 56' 35.5"
with an uncertainty of 3.0 arcseconds (radius, 90% containment). This
location is 44 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
2.17e+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/306793/. 

UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 152 seconds after the BAT trigger. A possible afterglow 
candidate has been found in the initial data products, at a magnitude of 
~19 mag. No correction has been made for the expected extinction corresponding
to E(B-V) of 0.19. The position of the tentative UVOT source is:
   RA(J2000)  = 06h 37m 53.6s
   Dec(J2000) = +23d 56' 34.1"

Burst Advocate for this burst is P. J. Brown (pbrown 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.)