GCN Circular 8035

A. M. Parsons (GSFC), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
D. N. Burrows (PSU), S. T. Holland (CRESST/USRA/GSFC),
E. A. Hoversten (PSU), S. D. Hunsberger (PSU), J. A. Kennea (PSU),
C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL),
D. Perez (U Leicester), T. Sakamoto (NASA/UMBC),
R. L. C. Starling (U Leicester), M. C. Stroh (PSU) and
T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team:

At 23:07:35 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080727C (trigger=318170).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 32.645, +64.151 which is 
   RA(J2000)  = 02h 10m 35s
   Dec(J2000) = +64d 09' 05"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows multiple peaks
with a duration of about 100 sec.  The peak count rate
was ~3500 counts/sec (15-350 keV), at ~25 sec after the trigger. 

The XRT began observing the field at 23:08:47.9 UT, 72.5 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
32.63384, 64.13771 which is equivalent to:
   RA(J2000)  = 02h 10m 32.12s
   Dec(J2000) = +64d 08' 15.8"
with an uncertainty of 2.8 arcseconds (radius, 90% containment). This
location is 50 arcseconds from the BAT onboard position, within the BAT
error circle. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (6.78e+21
cm^-2, Kalberla et al. 2005), with an excess column of 7.7
(+7.98/-6.22) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 1.30e-09 erg cm^-2 s^-1 (0.2-10
keV). 


UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 81 seconds after the BAT trigger. No afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of
the XRT error circle. The typical 3-sigma upper limit has been about 18.5 mag. 
The 8'x8' region for the list of sources generated on-board covers 100% of the
XRT error circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the large, but uncertain extinction expected. 




We note that the Galactic latitude of this source is 2.6 deg,
but we believe this to be a GRB based on the BAT and XRT lightcurves
and the spectral information. 

Burst Advocate for this burst is A. M. Parsons (parsons 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.)