[vsnet-grb-info 6049] GRB 080506: Swift detection of a burst with optical afterglow

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7685
SUBJECT: GRB 080506: Swift detection of a burst with optical afterglow
DATE:    08/05/06 18:06:27 GMT
FROM:    Wayne Baumgartner at GSFC  <wayne at milkyway.gsfc.nasa.gov>

W. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU),
M. M. Chester (PSU), G. Cusumano (INAF-IASFPA),
P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC),
C. Guidorzi (INAF-OAB), S. T. Holland (CRESST/USRA/GSFC),
S. Immler (CRESST/GSFC/UMD), J. A. Kennea (PSU),
V. La Parola (INAF-IASFPA), V. Mangano (INAF-IASFPA),
F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester),
C. Pagani (PSU), P. Romano (INAF-IASFPA), T. Sakamoto (NASA/UMBC),
M. Stamatikos (NASA/ORAU), T. N. Ukwatta (GSFC/GWU) and
H. Ziaeepour (UCL-MSSL) report on behalf of the Swift Team:

At 17:46:21 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080506 (trigger=311159).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 329.435, +39.002 which is 
   RA(J2000) = 21h 57m 44s
   Dec(J2000) = +39d 00' 08"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As this is an image trigger, the BAT light curve does 
not show meaningful emission from the burst. 

The XRT began observing the field at 17:48:41.3 UT, 140.1 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 329.42145, 38.98413 which
is equivalent to:
   RA(J2000)  = 21h 57m 41.15s
   Dec(J2000) = +38d 59' 02.9"
with an uncertainty of 3.3 arcseconds (radius, 90% containment). This
location is 74 arcseconds from the BAT onboard position, within the BAT
error circle. The XRT light curve from TDRSS data is fading. 

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/311159/. 

The initial flux in the 2.5 s image was 5.50e-09 erg cm^-2 s^-1 (0.2-10
keV). 


UVOT took a finding chart exposure of 400 seconds with the V filter starting
143 seconds after the BAT trigger. There is a candidate afterglow in the
rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	21:57:41.83 = 329.4243
  DEC(J2000) = +38:59:06.4  =  38.9851
with a 1-sigma error radius of about 0.5 arc sec. This position is 8.0 arc sec. 
from the center of the XRT error circle. The estimated magnitude is 18.3 with a
1-sigma error of about 0.5 mag. No correction has been made for the expected
extinction of about 0.8 magnitudes. 

Burst Advocate for this burst is W. H. Baumgartner (wayne 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.)