[vsnet-grb-info 20124] Swift trigger 755873 is not astrophysical

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22220
SUBJECT: Swift trigger 755873 is not astrophysical
DATE:    17/12/09 22:55:02 GMT
FROM:    Andrea Melandri at INAF-OAB  <andrea.melandri at brera.inaf.it>

A. Melandri, P. D'Avanzo (INAF-OAB), S. Barthelmy (GSFC), A. Lien (GSFC) report on behalf of the Swift Team:

We report further analysis of the Swift/BAT trigger #755873 (Barthelmy et al., GCN Circ. 22217) using the full data set from recent telemetry downlinks.

The BAT ground analysis uses the data set from T-60 to T+243 sec. The BAT image significance is only 4.6 sigma (15-350 keV).  Also, the mask-weighted light curve does not show anything significant.

We have analysed 0.8 ks of XRT downlinked data from 158 s to 940 s after the BAT trigger. The data are entirely in Photon Counting (PC) mode. No source is detected within the BAT error circle (Barthelmy et al., GCN Circ. 22217).

Considering the marginal detection by BAT and the non-detection of an afterglow by XRT, we conclude that this trigger was due to a statistical fluctuation and not to a real astrophysical source.