Proton Intensity Spectra during the May 17th, 2012 and January 6th, 2014 Solar Energetic Particle Events - Measurement Capabilities of the Electron Proton Helium Telescope on Board SOHO

Abstract:

Ground Level Enhancements are solar energetic particle events that show a significant intensity increase at energies that can be measured by ground based instrumentation, i.e. neutron monitors. In the recent history 71 GLEs have been recorded. The last one was the May 17, 2012 event that has not only been measured by more than one neutron monitor but also by sophisticated instrumentation in space like PAMELA and the Electron Proton Helium INstrument (EPHIN) aboard SOHO. The January 6, 2014 solar energetic particle (SEP) event led to an intensity increase of about 3 percent at both South Pole neutron monitors and was considered by Thakur et al. (2014) to be a GLE. Since only one pair of neutron monitors show an unambiguous increase the energy spectra for this event can only be determined by spacecraft like e.g. PAMELA or SOHO/EPHIN.

We show that the Electron Proton Helium INstrument at Langragian point L1 is capable to measure the proton energy spectra of solar energetic particle events at energies between 150 MeV and above 700 MeV. A GEANT Monte Carlo simulation has been performed to determine the energy response function of EPHIN for electrons, protons and heavier ions. As a result of this calculation we developed a method using energy loss information of particles measured in the detector stack that allow to derive the proton energy spectra in the range from about 150 MeV to more than 700 MeV. In order to validate our method we compared our results to the one obtained by PAMELA that was published by Bazilevskaya et al. (2013) for the May 2012 event.

Furthermore, the January 6, 2014 event spectrum in the given energy range is presented and discussed in comparison to the May 2012 event.