GCN Circular 7598

M. Stamatikos (NASA/ORAU), A. P. Beardmore (U Leicester),
N. Gehrels (NASA/GSFC), S. D. Hunsberger (PSU),
C. B. Markwardt (CRESST/GSFC/UMD), J. P. Osborne (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL),
T. Sakamoto (NASA/UMBC), R. L. C. Starling (U Leicester) and
E. Troja (U Leicester/INAF-IASFPA) report on behalf of the Swift
Team:

At 08:51:12 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080413B (trigger=309111).  Swift started slewing approximately 
70 seconds after the burst. The BAT on-board calculated location is 
RA, Dec 326.134, -19.969 which is 
   RA(J2000) = 21h 44m 32s
   Dec(J2000) = -19d 58' 08"
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 3 sec.  The peak count rate
was ~15,000 counts/sec (15-350 keV), at ~0.2 sec after the trigger. 

The XRT began observing the field at 08:53:23.8 UT, 131.2 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 326.14434,
-19.98104 which is equivalent to:
   RA(J2000)  = 21h 44m 34.64s
   Dec(J2000) = -19d 58' 51.7"
with an uncertainty of 2.6 arcseconds (radius, 90% containment). This
location is 55 arcseconds from the BAT onboard position, within the BAT
error circle. 

A power-law fit to a spectrum formed from promptly downlinked event
data does not constrain the column density, so we cannot provide limits
on the redshift using spectroscopy and the relation from Grupe et al. 
(2007). A summary of the promptly downlinked data is given at
http://www.swift.ac.uk/sper/309111/. 

UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 134 seconds after the BAT trigger. There is a candidate
afterglow in the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	21:44:34.68 = 326.1445
  DEC(J2000) = -19:58:52.0  = -19.9811
with a 1-sigma error radius of about 0.6 arc sec. This position is 0.6 arc
sec. from the XRT position. The estimated magnitude is 16.5
with a 1-sigma error of about 0.5 mag. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.04. 

Burst Advocate for this burst is M. Stamatikos (michael 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.)