GCN Circular 9860
Subject
Swift Trigger 361477, called GRB090831B, is probably not real.
Date
2009-09-01T12:45:04Z (16 years ago)
From
Massimiliano de Pasquale at MSSL-UCL <mdp@mssl.ucl.ac.uk>
J.R. Cummings (NASA/UMBC), P.A. Evans (U. Leicester), J.A. Kennea (PSU),
C. Pagani (PSU), and M. De Pasquale (MSSL/UCL) on behalf of the Swift
team report:
The ground analysis of BAT data from trigger 361477 (De Pasquale et al.,
GCN Circ. 9851) shows a very weak excess in the low energy bands only.
The response is consistent with a somewhat unusually large noise
fluctuation in the image domain caused by the presence of a bright source
in the BAT partially coded field of view (Cyg-X1).
The XRT observed the field for 3.23 ks between T0+150 s and T0+10 ks. The
data are entirely in Photon Counting mode. We do not find any source in
the field of view. A 3-sigma upper limit on covering the BAT onboard error
circle is 2.7 x 10^-3 ct/sec.
No new source is found in the UVOT white filter finding chart (153-303s
after the trigger) inside the BAT error circle down to a 3 sigma upper
limit of 20.9.
We conclude that the trigger is unlikely to be due to a GRB or any other
astrophysical source.