Ground level enhancement of December 13, 2006 observed by means of muon hodoscope

A wide-aperture hodoscope URAGAN detected a muon rate increase during GLE of December 13, 2006 at six sigma level (for ten-minute bins). Maximum of the enhancement was observed at 03:00 UTC. Capabilities of muon hodoscopes allow obtaining 2D-images of muon flux and for the first time the two-dimensional dynamics of GLE event was measured. Due to the fact that asymptotic view cone of the hodoscope appeared looking along IMF, it was possible to trace in details the evolution of a short-lived and highly collimated relativistic particle bunch in the initial phase of the event.