Parker Solar Probe Observations of Solar Energetic Particles Associated with a Slow Coronal Mass Ejection at 0.25AU

We analyze observations from ISOIS/EPI-Lo onboard Parker Solar Probe (PSP), of ~ 30-200 keV ions on Nov 11, 2018 when PSP was about 0.25AU from the Sun. At this time, PSP was on the opposite side of the Sun relative to Earth. About five hours before the onset of the solar energetic particle (SEP) event, a coronal mass ejection (CME) was observed by STEREO-A/Cor2 and the magnetic "flux rope" associated with this CME was observed to cross PSP about a day later. No shock wave was observed at PSP, and modeling suggests that there was either no shock, or a very weak one driven by the CME. The particle event was characterized by a distinctive velocity dispersion feature with higher energy protons arriving well before the lower energy ones. We suggest that the CME is the source of the SEP event. The timing of the first-arriving particles indicates they came from the CME when it was accelerating away from the Sun at about 7.5 solar radii. The particle intensities increased gradually from their onset over a period of a few hours, depending on their energy, reaching a peak, and then decayed gradually before the arrival of the CME at PSP. A significant drop in SEP intensity was observed during the passage of the CME magnetic flux rope itself. The event-averaged spectrum is very soft, suggesting a weak event. Analysis of anisotropies is consistent with the earliest arriving particles moving radially outward from the Sun, in approximately the same direction as the interplanetary magnetic field. Later in the event the anisotropy observations are consistent the advection of an isotropic distribution suggesting significant interplanetary scattering of these ions. We also show the results of numerical modeling of this event. The particle fluxes are reasonably well fit to solutions of the Parker transport equation assuming a moving source. From our modeling we derive diffusion coefficients and mean-free paths for 30-200keV protons.