[vsnet-grb-info 5323] GRB 071028: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7012
SUBJECT: GRB 071028: Swift detection of a burst
DATE:    07/10/28 18:00:32 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at lheamail.gsfc.nasa.gov>

J. L. Racusin (PSU), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), G. Cusumano (INAF-IASFPA),
N. Gehrels (NASA/GSFC), C. Gronwall (PSU), J. A. Kennea (PSU),
H. A. Krimm (GSFC/USRA), F. E. Marshall (NASA/GSFC),
P. T. O'Brien (U Leicester), C. Pagani (PSU), D. M. Palmer (LANL),
P. Romano (Univ. Bicocca & INAF-OAB), M. Stamatikos (NASA/ORAU),
M. C. Stroh (PSU), T. N. Ukwatta (GSFC/GWU) and L. Vetere (PSU)
report on behalf of the Swift Team:

At 17:41:01 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 071028 (trigger=295527).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 119.847, +21.498 which is 
   RA(J2000)  =  07h 59m 23s
   Dec(J2000) = +21d 29' 52"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  Even though this is an image trigger, there is
an indication of activity from about T+20 sec to T+50 sec. 
The peak count rate was ~400 counts/sec (15-350 keV), at ~25 sec
after the trigger. 

The XRT began observing the field at 17:42:59 UT, 118 seconds after the
BAT trigger. Using prompt downlinked data, we find a bright, variable, 
uncatalogued X-ray source located at RA, Dec 119.8176, 21.4841 which is
   RA(J2000)  = 07 59 16.22
   Dec(J2000) = +21 29 02.8
with an uncertainty of 4.1 arcsec (radius, 90% containment). 
This location is 106 arcseconds from the BAT on-board position,
within the BAT error circle. The initial flux in the 2.5s image
was 7.2e-10 erg/cm2/s (0.2-10 keV). 

UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 128 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.   There is a bright (12th mag) star in the XRT error circle
which severely limits our ability to detect a possible afterglow.  No correction
has been made for extinction. 

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.)