Mean High Energy Ionic Charge States of the September 2017 Solar Energetic Particle Events in ACE and STEREO Data

We have previously reported mean high-energy ionic charge states of solar energetic particles (SEPs) using the method of Sollitt et al. (2008). The method applies to abundant elements (e.g. N, O, Ne, Mg, Si, and Fe) in SEP events at the energy ranges covered by the STEREO/LET instrument (e.g. 2.7-70 MeV/nuc for Fe) and the ACE/SIS instrument (e.g. 11-168 MeV/nuc for Fe), as well as lower energy measurements by STEREO/SIT and ACE/ULEIS to provide additional constraint to the charge state calibration.

The Solar Energetic Particle (SEP) events of September 2017 were visible to both the ACE spacecraft and the STEREO Ahead spacecraft. These events included the September 10 event also detected as a ground level event. The time intensity profiles in these events in both the ACE/SIS instrument and the STEREO/LET instrument both show periods of exponential time decay, making the events potentially amenable to charge states analysis using the method of Sollitt et al. (2008). We will report on analysis of these events using both ACE and STEREO data to attempt to obtain multi-spacecraft observations of these events for charge states. We will also report on continuing developments in the technique to optimize and automate the selection of exponential decay periods for analysis.