TITLE:   GCN CIRCULAR
NUMBER:  7442
SUBJECT: GRB 080319C: Swift detection of a burst with an optical afterglow
DATE:    08/03/19 12:45:58 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott@lheamail.gsfc.nasa.gov>

C. Pagani (PSU), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
D. N. Burrows (PSU), P. A. Evans (U Leicester),
N. Gehrels (NASA/GSFC), O. Godet (U Leicester),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
V. Mangano (INAF-IASFPA), J. P. Osborne (U Leicester),
K. L. Page (U Leicester), A. M. Parsons (GSFC), J. L. Racusin (PSU),
B. Sbarufatti (INAF-IASFPA), M. Stamatikos (NASA/ORAU),
R. L. C. Starling (U Leicester), G. Stratta (ASDC) and
T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team:

At 12:25:56 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080319C (trigger=306778).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 258.973, +55.410 which is 
   RA(J2000)  =  17h 15m 54s
   Dec(J2000) = +55d 24' 35"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows several overlapping FRED-like
peaks starting at T+0 and ending around T+20 sec.  The peak count rate
was ~8000 counts/sec (15-350 keV), at ~T+0 sec after the trigger. 

The XRT began observing the field at 12:29:40 UT, 224 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 258.9828, 55.3920
which is equivalent to:
   RA(J2000)  = 17h 15m 55.86s
   Dec(J2000) = +55d 23' 31.2"
with an uncertainty of 4.5 arcseconds (radius, 90% containment). This
location is 3 arcseconds from the optical afterglow candidate position. 

UVOT took a finding chart exposure of 100 seconds with the White   
(160-650 nm) filter starting 227 seconds after the BAT trigger. There
is a candidate afterglow in the rapidly available 2.7'x2.7' 
sub-image at   

  RA(J2000)  =	17:15:55.51 = 258.9813   
  DEC(J2000) = +55:23:30.8  = +55.3919    

with a 1-sigma error radius of  about 0.5 arc sec. This position
is 67.4 arc sec. from the center of  the BAT error circle.  This
is consistent with the KAIT position (Li  et al., 2008, GCNC 7441). 
The estimated magnitude is white = 18.8 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 0.03. 

Burst Advocate for this burst is C. Pagani (pagani AT astro.psu.edu). 
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.)