[vsnet-grb-info 6372] GRB 080721: Swift detection of a burst with a bright optical counterpart.

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7988
SUBJECT: GRB 080721: Swift detection of a burst with a bright optical counterpart. 
DATE:    08/07/21 10:42:45 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

F. E. Marshall (NASA/GSFC), A. P. Beardmore (U Leicester),
D. N. Burrows (PSU), P. A. Evans (U Leicester),
N. Gehrels (NASA/GSFC), C. Gronwall (PSU), C. Guidorzi (INAF-OAB),
S. T. Holland (CRESST/USRA/GSFC), V. Mangano (INAF-IASFPA),
P. T. O'Brien (U Leicester), J. P. Osborne (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL),
D. Perez (U Leicester), M. Perri (ASDC), B. Preger (ASDC),
P. Romano (INAF-IASFPA), M. Stamatikos (NASA/ORAU),
R. L. C. Starling (U Leicester), T. N. Ukwatta (GSFC/GWU),
P. A. Ward (MSSL-UCL) and H. Ziaeepour (UCL-MSSL) report on behalf of
the Swift Team:

At 10:25:16 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080721 (trigger=317508).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 224.471, -11.712 which is 
   RA(J2000) = 14h 57m 53s
   Dec(J2000) = -11d 42' 43"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed at least 4 peaks
structure with a duration of about 35 sec.  The peak count rate
was ~19k counts/sec (15-350 keV), at ~0 sec after the trigger,
during the second peak. 

The XRT began observing the field at 10:27:04.1 UT, 107.2 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 224.4899, -11.7242 which is equivalent to:
   RA(J2000)  = 14h 57m 55.9s
   Dec(J2000) = -11d 43' 27.3"
with an uncertainty of 4.7 arcseconds (radius, 90% containment). This
location is 79 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy. 

UVOT took a finding chart exposure of nominal 100 seconds with the White
(160-650 nm) filter starting 180 seconds after the BAT trigger. There is a
candidate afterglow in the list of sources generated on-board at
  RA(J2000)  =  14:57:55.8 = 224.48268
  DEC(J2000) = -11:43:25   = -11.72361
with a 1-sigma error radius of about 1.0 arc sec. The estimated white
magnitude is 14.6 with a 1-sigma error of about 0.01 mag. No correction
has been made for Galactic extinction. 

Burst Advocate for this burst is F. E. Marshall (marshall 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.)