[vsnet-grb-info 5950] GRB 080413: Swift detection of a burst with an optical afterglow

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7594
SUBJECT: GRB 080413: Swift detection of a burst with an optical afterglow
DATE:    08/04/13 03:06:53 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

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

At 02:54:19 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080413 (trigger=309096).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 287.290, -27.679 which is 
   RA(J2000) = 19h 09m 10s
   Dec(J2000) = -27d 40' 44"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a triple-peaked
structure with a duration of about 55 sec.  The peak count rate
was ~10000 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 02:55:20.0 UT, 60.7 seconds after
the BAT trigger. XRT found a bright, fading uncatalogued X-ray source
located at RA, Dec 287.2978, -27.6779 which is equivalent to:
   RA(J2000)  = 19h 09m 11.4s
   Dec(J2000) = -27d 40' 40.4"
with an uncertainty of 4.7 arcseconds (radius, 90% containment). This
location is 25 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to assess possible
redshift constraints using X-ray spectroscopy and the nH-z relation
from Grupe et al. (2007). 


UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 76 seconds after the BAT trigger. There is a candidate
afterglow in the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	19:09:11.76 = 287.2990
  DEC(J2000) = -27:40:40.1  = -27.6778
with a 1-sigma error radius of about 0.6 arc sec. This position is 3.9 arc sec. 
from the center of the XRT error circle. The estimated magnitude is 15.2 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 0.16.