TITLE: GCN CIRCULAR NUMBER: 10742 SUBJECT: Swift-BAT trigger 421695 is likely not astrophysical DATE: 10/05/11 20:46:36 GMT FROM: Boris Sbarufatti at INAF-OAB/IASFPA B. Sbarufatti (INAF-OAB/IASFPA), R. Margutti (INAF-OAB), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), S.T. Holland (GSFC/USRA), H. A. Krimm (GSFC/USRA) The BAT data set from T-61 to T+302 sec from the recent telemetry downlink suggests that trigger 421695 (Sbarufatti et al., GCN Circ 10737) is likely not of astrophysical origin, but is instead most likely due to a chance superposition of a rate increase with an upward fluctuation in the image domain. The best fit image significance is 7.1 sigma. The excess rate is seen only in the lowest energy band, which is inconsistent with a short, but faint, GRB. The galactic latitude (+10.1 degrees) and short duration argue against its being a galactic transient and the lack of association with any of the 370 nearby galaxies in the GCN ground catalog is an argument against its being an SGR giant flare from a nearby galaxy. However, since the trigger has neither the spectral nor temporal signature of an electronic noise or cosmic ray event, we cannot absolutely rule out the possibility that the trigger is of astrophysical origin. Swift-XRT obtained 2 ks of Photon Counting (PC) mode data, from T0+72 s to T0+2 ks. No source is found in the BAT error circle, with a 3-sigma upper limit of 5 x 10-3 ct/sec; for a typical GRB, this would correspond to an upper limit on the observed 0.3-10 keV flux of 2 x 10-13 erg cm-2 s-1. No credible afterglow candidate has been found in the UVOT data products relative to the USNO B1.0 catalogue. The estimated 3-sigma upper limit is white > 20.8 mag. No correction has been made for the expected Galactic extinction corresponding to a reddening of 0.33 mag. Photometry is on the UVOT photometry system of Poole et al. (2008). Recent problems within the Goddard network (that blocked email to and from the circulars-processing computer), a duplicated (GCN Circ 10741) of the original Swift circular on trigger 421695 (GCN Circ 10737) was distributed. GCN Circ 10741 has been removed from the archives. Apologies for the confusion.