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Published February 2020 | Supplemental Material + Accepted Version + Published
Journal Article Open

Observations of the 2019 April 4 Solar Energetic Particle Event at the Parker Solar Probe


A solar energetic particle event was detected by the Integrated Science Investigation of the Sun (IS⊙IS) 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 (cm² 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° 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.

Additional Information

© 2020. The American Astronomical Society. Received 2019 September 27; revised 2019 October 31; accepted 2019 November 11; published 2020 February 3. Early Results from Parker Solar Probe: Ushering a New Frontier in Space Exploration This work was supported by NASA under contract NNN06AA01C. Parker Solar Probe was designed, built, and is now operated by the Johns Hopkins University Applied Physics Laboratory as part of NASA's Living With a Star (LWS) program. Support from the LWS management and technical team has played a critical role in the success of this mission. We appreciate the contributions of the many individuals who have made PSP the successful mission that it is, in particular the EPI-Hi engineers W. R. Cook, B. Kecman, G. Dirks, and N. Angold. We gratefully acknowledge the test and calibration support provided by Michigan State University's National Superconducting Cyclotron Laboratory, Texas A&M University's Cyclotron Institute, and the Lawrence Berkeley National Laboratory's 88-inch Cyclotron Laboratory. The ISʘIS data and visualization tools are available to the community at https://spacephysics.princeton.edu/missions-instruments/isois; data are also available via the NASA Space Physics Data Facility (https://spdf.gsfc.nasa.gov/).We thank the GONG and Wilcox Solar Observatory teams for making their data readily accessible online. S.D.B. acknowledges the support of the Leverhulme Trust Visiting Professorship program.

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Accepted Version - 1912.03384.pdf

Supplemental Material - apjsab5712f10_video.mp4


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