[vsnet-grb-info 6408] GRB 080727B: Swift detection of a bright burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8022
SUBJECT: GRB 080727B: Swift detection of a bright burst
DATE:    08/07/27 08:30:44 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

S. Immler (CRESST/GSFC/UMD), W. H. Baumgartner (GSFC/UMBC),
A. P. Beardmore (U Leicester), P. A. Evans (U Leicester),
C. Guidorzi (INAF-OAB), S. D. Hunsberger (PSU), W.B Landsman (GSFC),
C. B. Markwardt (CRESST/GSFC/UMD), K. L. Page (U Leicester),
D. M. Palmer (LANL), A. M. Parsons (GSFC), D. Perez (U Leicester),
T. Sakamoto (NASA/UMBC) and R. L. C. Starling (U Leicester) report on
behalf of the Swift Team:

At 08:13:24 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080727B (trigger=318101).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 276.870, +1.172 which is 
   RA(J2000) = 18h 27m 29s
   Dec(J2000) = +01d 10' 20"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a double-peaked
structure with a duration of about 10 sec.  The peak count rate
was ~18,000 counts/sec (15-350 keV), at 6 sec after the trigger. 

The XRT began observing the field at 08:15:05.9 UT, 101.2 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 276.85898,
1.16304 which is equivalent to:
   RA(J2000)  = 18h 27m 26.16s
   Dec(J2000) = +01d 09' 47.0"
with an uncertainty of 2.8 arcseconds (radius, 90% containment). This
location is 51 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 (3.64e+21
cm^-2, Kalberla et al. 2005), with an excess column of 4.7
(+4.37/-3.38) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm)  filter starting 105 seconds after the BAT trigger. No
afterglow candidate has  been found in the initial data products. The
2.7'x2.7' sub-image covers 25% of  the BAT error circle and 100% of
the XRT error circle. The typical 3-sigma upper limit has been about
18.5 mag. No  correction has been made for the expected extinction
corresponding to E(B-V) of  1.94. 

Burst Advocate for this burst is S. Immler (immler 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.)