High energy ions associated with the SEP event on May 22, 2013

A Solar Energetic Particle (SEP) was detected by the Electron Proton and Alpha Monitor (EPAM) onboard of the Advanced Composition Explorer (ACE) spacecraft on 2013 May 22 both in the electrons and ion channels. In the electrons channels, it is a prompt fast rising highly isotropic event. There is an evidence in the ion channels of protons with energy above 1 GeV arriving essentially at the same time of the electrons. Although EPAM detected protons at sufficiently high energies, the global network of ground-based neutron monitors did not detected any increase in cosmic ray intensity, hence this event is not part of the list of Ground Level Events (GLEs) and since no significant increase of the count rate of at least two different high altitude stations is seen, it seems to fail even the Sub-GLE classification criteria. Comparing the SEP release time with Soft X-Ray (SXR) data on board of Geostationary Operational Environmental Satellites (GOES) spacecraft, we find that the particles were released after the peak in emission of the SXR, which implies that these particles likely do not have a flare origin. Radio data from ground based observatories show type II and type IV emissions at the time of particle release, therefore these particles could either be accelerated in the magnetic restructuring in the aftermath of a Coronal Mass Ejection (CME) or in an associated shock. We discuss both possibilities.