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GCN Circular 9860

Subject

Swift Trigger 361477, called GRB090831B, is probably not real.

Event

GRB 090831B

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. 9851Loading...
 
 ) 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.