Multispacecraft Energetic Particle Enhancements Associated with a Single Corotating Interaction Region

The radial evolution of particles accelerated at corotating interaction regions (CIRs) is not fully understood, particularly the distance range over which this particle acceleration occurs and how the energy spectra are modulated by transport through the inner heliosphere. Here, we present observations of energetic proton enhancements associated with a CIR observed by Parker Solar Probe on 2021 April 25 during the inbound leg of its orbit near similar to 46 R s (similar to 0.21 au). The CIR is identified at additional spacecraft (Solar Terrestrial Relations Observatory, STEREO-A; Solar Orbiter, SolO; and Advanced Composition Explorer, ACE) using a corotation time delay estimation, and energetic proton spectra from each spacecraft are compared. We find that (1) energetic protons are observed near 46 R s streaming sunward ahead of the CIR; (2) the CIR persists for at least one solar rotation and the corresponding energetic proton enhancements are observed at STEREO-A, SolO, and ACE; and (3) the proton energy spectrum is steeper near the Sun and hardens near 1 au. This observation presents the closest in situ energetic particle observation of a CIR to the Sun ever recorded. Results presented here suggest that particles can be accelerated by CIR structures within 1 au and these particles can penetrate very deep into the inner heliosphere.