Proton intensity spectra during the solar energetic particle events of May 17, 2012 and January 6, 2014

¹ Institute for experimental and applied physics, University Kiel, 24118 Kiel, Germany
e-mail: kuehl@physik.uni-kiel.de
² Space Research Group, University of Alcalá, 28871 Alcalá de Henares, Spain

Received: 28 August 2014
Accepted: 18 March 2015

Abstract

Context. Ground-level enhancements (GLEs) are solar energetic particle events that show a significant intensity increase at energies that can be measured by neutron monitors. The most recent GLE-like events were recorded on May 17, 2012 and January 6, 2014. They were also measured by sophisticated instrumentation in space such as PAMELA and the Electron Proton Helium INstrument (EPHIN) onboard SOHO. Since neutron monitors are only sensitive to protons above 400 MeV with maximum sensitivity at 1 to 2 GeV, the spectra of such weak GLE-like events (January 6, 2014) can only be measured by space instrumentation.

Aims. We show that the SOHO/EPHIN is capable of measuring the solar energetic particle proton event spectra between 100 MeV and above 800 MeV.

Methods. We performed a GEANT Monte Carlo simulation to determine the energy response function of EPHIN. Based on this calculation, we derived the corresponding proton energy spectra. The method was successfully validated against previous PAMELA measurements.

Results. We present event spectra from EPHIN for May 17, 2012 and January 6, 2014. During the event in May 2012, protons were accelerated to energies above 700 MeV, while we found no significant increase for protons above 600 MeV during the event on January 6, 2014.