[vsnet-grb-info 5775] GRB 080319B: Swift detection of an intense burst with a bright optical counterpart

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7427
SUBJECT: GRB 080319B: Swift detection of an intense burst with a bright optical counterpart
DATE:    08/03/19 06:32:26 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

J. L. Racusin (PSU), N. Gehrels (NASA/GSFC),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
C. B. Markwardt (CRESST/GSFC/UMD), C. Pagani (PSU),
D. M. Palmer (LANL) and M. Stamatikos (NASA/ORAU) report on behalf of
the Swift Team:

At 06:12:49 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080319B (trigger=306757).  Swift slewed immediately to
the burst. The BAT on-board calculated location is 
RA, Dec 217.926, +36.303 which is
   RA(J2000) = 14h 31m 42s
   Dec(J2000) = +36d 18' 10"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed one bright but
complex peak with a duration of about 50 sec, with an extended tail.  
The peak count rate was ~70,000 counts/sec (15-350 keV), at ~20 sec 
after the trigger. 

The XRT began observing the field at 06:13:49.7 UT, 60.5 seconds after
the BAT trigger. XRT found a very bright fading, uncatalogued X-ray 
source located at RA, Dec 217.9196, +36.3041 which is equivalent to:
   RA(J2000)  = 14h 31m 40.7s
   Dec(J2000) = +36d 18' 14.7"
with an uncertainty of 4.7 arcseconds (radius, 90% containment). This
location is 18 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 400 seconds with the V filter
starting  175 seconds after the BAT trigger. There is a candidate
afterglow in the  rapidly available 2.7'x2.7' sub-image. This
position is consistent with  the XRT error circle, but the source is
so bright that a precise UVOT position  is not possible due to
saturation effects. The estimated magnitude is 11.5 with a  1-sigma
error of about 0.5 mag. No correction has been made for the expected 
extinction of about 0.04 magnitudes. 

Burst Advocate for this burst is J. L. Racusin (racusin 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.)