[vsnet-grb-info 9847] Swift Trigger 435520 is probably not a GRB

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  11315
SUBJECT: Swift Trigger 435520 is probably not a GRB
DATE:    10/10/03 09:41:04 GMT
FROM:    Jamie A. Kennea at PSU/Swift-XRT  <kennea at astro.psu.edu>

J. R. Cummings (NASA/UMBC), D. N. Burrows (PSU),
O. Godet (U Leicester), C. Guidorzi (U Ferrara),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
W.B Landsman (GSFC), V. Mangano (INAF-IASFPA), R. Margutti (INAF-OAB),
C. B. Markwardt (NASA/GSFC), A. Melandri (INAF-OAB),
K. L. Page (U Leicester), B. Sbarufatti (INAF-OAB/IASFPA) and
C. A. Swenson (PSU) report on behalf of the Swift Team:

At 09:18:01 UT, the Swift Burst Alert Telescope (BAT) triggered and
located trigger 435520.  Swift slewed immediately to the location. 
The BAT on-board calculated location is RA, Dec 300.937, +32.386 which is 
   RA(J2000) = 20h 03m 45s
   Dec(J2000) = +32d 23' 11"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve does not show any obvious
signal, which is typical for image triggers.  Based on ground processing
of flight detector image data, the significance is 6.2 sigma, which 
would not normally exceed the detection criteria.  We would need additional
event-by-event data processed on the ground to clarify the significance. 

The XRT began observing the field at 09:20:24.85 UT,   143.1 seconds after
the BAT trigger. No source was detected in the promptly available XRT
data. We are waiting for the full dataset to detect and localise the
XRT counterpart. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 147 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers 25% of
the BAT error circle. Because of the density of catalogued stars, further
analysis is required to report an upper limit for any afterglow in the
sub-image. The coverage of the BAT error circle by the 8'x8' region for the
list of sources generated on-board is uncertain because the large number of
sources filled the available telemetry. Because of the density of catalogued
stars, further analysis is required to report an upper limit for any afterglow
in the region. No correction has been made for the large, but uncertain
extinction expected.