TITLE: GCN CIRCULAR NUMBER: 14701 SUBJECT: Swift Trigger 556533 is not an astrophysical event DATE: 13/05/24 14:04:50 GMT FROM: Hans Krimm at NASA-GSFC S. D. Barthelmy (GSFC), A. P. Beardmore (U Leicester), H. A. Krimm (CRESST/GSFC/USRA), and M. H. Siegel (PSU) report on behalf of the Swift Team: We conclude that subthreshold trigger #556533 (Beardmore, et al., GCN Circ. 14699) was caused by a cosmic ray shower and chance coincidence and is not due to a GRB or other astrophysical phenomenon. Using the data set from T-240 to T+963 sec from the recent telemetry downlink, we report that the full Swift/BAT event data shows no significant features in the light curve. The Swift/XRT began settled observations of the field of trigger #556533 155 s after the BAT trigger. There is nothing visible in the XRT data at the position of the BAT onboard error circle, or in the entire image. The XRT upper limit is 0.01 c/s in 614 s of PC mode data. The Swift/UVOT began settled observations of the field of trigger #556533 155 s after the BAT trigger. No optical afterglow consistent with the BAT position is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag u_FC 155 405 246 >19.7 v 460 629 39 >18.3 b 410 724 55 >19.1 u 155 703 285 >19.7 w1 510 678 39 >18.2 w2 584 604 19 >17.9 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.85 in the direction of the burst (Schlegel et al. 1998).