Mean High-Energy Ionic Charge States during the September 2017 Solar Energetic Particle Events Observed by ACE and STEREO

We have reported mean high-energy ionic charge states of solar energetic particle (SEP) events for Solar Cycles 23 and 24, 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 over 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, which provide additional constraints to the charge state calibration. The SEP events of September 2017 were visible at both spacecraft, when STEREO/AHEAD and ACE were separated by ~128 degrees in heliospheric longitude. These events included the September 10 event also detected as a ground level event. The time intensity profiles in some of these events in both the ACE/SIS instrument and the STEREO/LET instrument both show periods of exponential time decay, making the events amenable to charge states analysis using the method of Sollitt et al. (2008). We will report mean ionic charge states for these events using both ACE and STEREO, comparing the measurements to demonstrate longitude-dependence in charge states, if any. We will also compare these results individually with measurements from other SEP events and with previously observed correlation between charge states and abundance ratios.