2012 May 17th GLE: New Views of a GLE with PAMELA

The properties of solar energetic particles (SEPs) have long been modeled to constrain the proposed scenarios for particle acceleration. The challenge, however, is that the signatures of acceleration gleaned from SEP observations are modified as a consequence of transport within interplanetary space. During transport, an interesting subject in its own right, solar energetic particles are subject to pitch angle scattering by the turbulent magnetic field, adiabatic focusing, and/or reflections at large-scale magnetic structures. The highest energy anisotropic SEPs, so- called Ground Level Enhancements (GLEs), provide an ideal way to study acceleration with minimal complications from transport. The different morphologies of anisotropic GLEs and SEPs measured in space at lower energies has led many to believe that two distinct acceleration processes are at work. The unique observations from the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) instrument, provide an essential link between the highest energy GLEs and the low-energy in-situ observations. PAMELA observations bridge a critical gap in energy while also providing unique pitch angle measurements above several GeV making it possible for the first time to constrain the effects of transport over a broad range in energy. In this work, we present unique high-energy SEP observations from PAMELA of the 2012 May 17 GLE and interpret the observed pitch angle distributions as a function of energy as a result of local (1 AU) scattering.