TITLE: GCN CIRCULAR NUMBER: 22563 SUBJECT: Swift Trigger 819863 is not a GRB DATE: 18/03/30 03:23:32 GMT FROM: David Palmer at LANL A. Deich (PSU), H. A. Krimm (NSF/USRA), F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL) and A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 03:09:02 UT, the Swift Burst Alert Telescope (BAT) triggered during the count rate increase during the approach to the SAA, and found a low-significance peak in the resulting image (trigger=819863). Swift slewed immediately to the location. The BAT on-board calculated location is RA, Dec 95.803, -64.954 which is RA(J2000) = 06h 23m 13s Dec(J2000) = -64d 57' 12" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a continuous increase as expected on entering the SAA. The XRT began observing the field at 03:10:27.2 UT, 85.1 seconds after the BAT trigger. However, the source automatically identified on-board was a cosmic ray, caused by the proximity of Swift to the SAA. Due to the low significance of the image (6.55 sigma), the lack of a GRB-like peak during the increasing particle background, and the non-detection of an afterglow by XRT, we believe that this is not a GRB.