GCN Circular 7362

S. T. Holland (CRESST/USRA/GSFC), S. D. Barthelmy (GSFC),
D. N. Burrows (PSU), J. R. Cummings (NASA/UMBC),
G. Cusumano (INAF-IASFPA), P. A. Evans (U Leicester),
N. Gehrels (NASA/GSFC), O. Godet (U Leicester),
C. Guidorzi (INAF-OAB), S. D. Hunsberger (PSU), J. A. Kennea (PSU),
V. Mangano (INAF-IASFPA), C. B. Markwardt (CRESST/GSFC/UMD),
A. Moretti (INAF-OAB), P. T. O'Brien (U Leicester),
J. P. Osborne (U Leicester), C. Pagani (PSU),
K. L. Page (U Leicester), D. M. Palmer (LANL),
D. Perez (U Leicester), P. Romano (INAF-IASFPA), G. Sato (GSFC/ISAS),
M. Stamatikos (NASA/ORAU), R. L. C. Starling (U Leicester) and
E. Troja (U Leicester/INAF-IASFPA) report on behalf of the Swift
Team:

At 11:23:30 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080307 (trigger=305011).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 136.633, +35.168 which is 
   RA(J2000) = 09h 06m 32s
   Dec(J2000) = +35d 10' 06"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a FRED
structure with a duration of at least 30 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 11:25:10.1 UT, 99.3 seconds after
the BAT trigger. Using promptly downlinked data we find a bright, fading
uncatalogued X-ray source with an enhanced position: RA, Dec 136.62833,
35.13866 which is equivalent to:
   RA(J2000)  = 09h 06m 30.80s
   Dec(J2000) = +35d 08' 19.2"
with an uncertainty of 2.6 arcseconds (radius, 90% containment). This
location is 106 arcseconds from the BAT onboard position, within the
BAT error circle. No prompt spectrum is yet available to assess possible
redshift constraints using X-ray spectroscopy and the nH-z relation
from Grupe et al. (2007). 

The initial flux in the 2.5 s image was 7.63e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 105 seconds after the BAT trigger. A possible fading source
that is not present in the DSS has been found in the initial data products at

    RA(J2000.0) =  09:06:25.5
   Dec(J2000.0) = +35:08:39

with an estimated uncertainty of 0.6 arcsec (radius, 90% confidence).  This
source is approximately 1 arcminute from the XRT position, which is too far
away to be consistent with the X-ray source.  The estimated white magnitude
 is 19.6 +/- 0.1.  No correction has been made for the expected
extinction corresponding to E(B-V) of 0.03 mag. 

Burst Advocate for this burst is S. T. Holland (sholland AT milkyway.gsfc.nasa.gov). 
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.)