[vsnet-grb-info 3938] GRB 061027: Swift detection of a possible burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  5760
SUBJECT: GRB 061027: Swift detection of a possible burst
DATE:    06/10/27 10:48:55 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), S. Campana (INAF-OAB), M. M. Chester (PSU),
G. Cusumano (INAF-IASFPA), N. Gehrels (NASA/GSFC),
C. Guidorzi (Univ Bicocca&INAF-OAB), K. M. McLean (LANL/UTD),
T. Mineo (INAF-IASFPA), P. T. O'Brien (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL),
S. B. Pandey (UCL-MSSL), P. Romano (Univ. Bicocca & INAF-OAB) and
T. Sakamoto (NASA/ORAU) report on behalf of the Swift Team:

At 10:15:02 UT, the Swift Burst Alert Telescope (BAT) triggered and
located possible GRB 061027 (trigger=235645).  Swift slewed immediately
to the burst.  The BAT on-board calculated location is 
RA,Dec 270.812, -82.228 {18h 03m 15s, -82d 13' 39"} (J2000)
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  This is a 64-sec image trigger and as is typical
the BAT lightcurve does not show any significant emission.  The image
peak is barely above the significance threshold for automatic
detection, and therefore this may be a statistical fluctuation. 

The XRT began taking data at 10:17:29 UT, 147 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. Initial down-linked
data products also show no evidence for any X-ray source in the image
in ~200 s of data. This gives a very rough upper limit of 
2E-12 erg/cm2/s for any source in the field of view.  We note 
that only one long burst has had no XRT detection following a 
prompt slew, out of 119 long GRBs observed by XRT with prompt 
slews to date.  Further analysis awaits the full dowloaded 
data products. 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 151.7 seconds after the BAT trigger. No
afterglow candidate has been found in the initial data products. The
limiting magnitude of the finding chart image is approximately 19.0. 
No correction has been made for the expected extinction.