[vsnet-grb-info 10731] Swift trigger 457076 is not a GRB

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  12154
SUBJECT: Swift trigger 457076 is not a GRB
DATE:    11/07/12 12:26:04 GMT
FROM:    Hans Krimm at NASA-GSFC  <hans.a.krimm at nasa.gov>

H. A. Krimm (CRESST/GSFC/USRA), S. D. Barthelmy (GSFC),V. D'Elia (ASDC),
C. B. Markwardt (NASA/GSFC), D. M. Palmer (LANL),  G. Stratta (ASDC)

Based on a non-detection in the XRT and a low significance in the BAT,
we conclude thatSwift/BAT trigger 457076 (Krimm et al, GCN 12149) was
most likely caused by a chance fluctuation in the BAT image domain
and is not due to a burst or other astrophysical phenomenon.

XRT began observing the field of the Swift trigger 457076 (Krimm et al.,
GCN circ 12149) 167 s after the burst trigger. We analyzed the first
2.6 ks of XRT data, from 167 s until 10 ks after the trigger. No
candidate afterglow is detected in the BAT error circle, and the
three sigma upper limit for any new source in the field of view is
4.3e-3 counts/second.

We examined the BAT event data from T-60 to T+243, when a slew took
the trigger position out of the field of view. The significance of
the event is reduced in ground processing to 5.5 sigma.  The light
curve shows a positive excess in the two lowest energy bands as
would be expected from an image trigger, but the increase is only
during the trigger interval, and the two bands are only weakly
correlated with each other.  There is no indication of earlier
or later emission.  This result, combined with the null result
from the XRT, leads us to our conclusion.