TITLE: GCN CIRCULAR NUMBER: 17800 SUBJECT: Confirmation that Swift Trigger 639636 is not astrophysical DATE: 15/05/03 01:25:25 GMT FROM: Scott Barthelmy at NASA/GSFC S. D. Barthelmy (GSFC), A. Maselli (INAF-IASFPA), M. Siegel (PSU), P. Kuin (MSSL) report: We conclude that Swift trigger #639636 (Maselli, et al., GCN Circ. 17799) was the result a noise fluctuation in BAT and is not due to a GRB or other astrophysical event. We have analyzed the BAT data set from T-239 to T+680 sec from recent telemetry downlinks. We find that ground analysis results in the significance dropping to 4.1 sigma from T+0 to T+60 s. Using 4.4 ks of XRT data, there is no significant counterpart detected within the BAT error circle at a three sigma upper limit of 2.84E-03 cts/s. The UVOT finding chart shows no new source to a limit of 19.6 mag in white.