[vsnet-grb-info 3646] GRB 060826(?): Swift detection of a possible burst

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  5480
SUBJECT: GRB 060826(?): Swift detection of a possible burst
DATE:    06/08/26 10:36:35 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at lheamail.gsfc.nasa.gov>

M. Stamatikos (NASA/ORAU), S. D. Barthelmy (GSFC),
D. N. Burrows (PSU), M. M. Chester (PSU), N. Gehrels (NASA/GSFC),
C. Guidorzi (Univ Bicocca&INAF-OAB), S. T. Holland (GSFC/USRA),
K. L. Page (U Leicester), D. M. Palmer (LANL), A. M. Parsons (GSFC),
M. C. Stroh (PSU) and H. Z. Ziaeepour (UCL-MSSL) report on behalf of
the Swift Team:

At 09:58:14 UT, the Swift Burst Alert Telescope (BAT) triggered and
located a possible GRB 060826 (trigger=226614).  Swift slewed immediately
to the burst.  The BAT on-board calculated location is 
RA,Dec 208.219, +11.871 {13h 52m 53s, +11d 52' 16"} (J2000)
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The lightcurve shows little structure, which is
typical for image triggers.  Given the little information received to date
on this trigger, we can not rule out a non-astrophysical cause
for this trigger. 

The XRT began taking data at 10:00:20 UT, 126 seconds after the BAT
trigger. The XRT on-board centroid algorithm did not find a source in
the image and no prompt position is available. In 285 seconds of
downlinked data, we find no concentration of photons at all. We note
that the non-detection of a long burst by the XRT after a prompt slew
is extremely unusual. We are waiting for more complete down-linked
data to perform a more sensitive search for a faint source in the BAT
error circle. 

UVOT took a finding chart exposure of 100 seconds with the uvm2
(166-268 nm) filter starting 123.7 seconds after the BAT trigger. No
images in optical filters were taken due to a bright star in the
field of view. No afterglow candidate has been found in the initial
data products. The 8'x8' region for the list of sources generated
on-board covers 25% of the BAT error circle. The list of sources is
typically complete to about 18 mag. No correction has been made for
the expected extinction corresponding to E(B-V) of 0.026.