A solar energetic particle event was detected by the Integrated Science
Investigation of the Sun (ISOIS) instrument suite on Parker Solar Probe (PSP)
on 2019 April 4 when the spacecraft was inside of 0.17 au and less than 1 day
before its second perihelion, providing an opportunity to study solar particle
acceleration and transport unprecedentedly close to the source. The event was
very small, with peak 1 MeV proton intensities of ~0.3 particles (cm^2 sr s
MeV)^-1, and was undetectable above background levels at energies above 10 MeV
or in particle detectors at 1 au. It was strongly anisotropic, with intensities
flowing outward from the Sun up to 30 times greater than those flowing inward
persisting throughout the event. Temporal association between particle
increases and small brightness surges in the extreme-ultraviolet observed by
the Solar TErrestrial RElations Observatory, which were also accompanied by
type III radio emission seen by the Electromagnetic Fields Investigation on
PSP, indicates that the source of this event was an active region nearly 80
degrees east of the nominal PSP magnetic footpoint. This suggests that the
field lines expanded over a wide longitudinal range between the active region
in the photosphere and the corona.
