Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published May 10, 2021 | Published
Journal Article Open

First Observations of Anomalous Cosmic Rays in to 36 Solar Radii

Abstract

NASA's Parker Solar Probe mission continues to travel closer to the Sun than any prior human-made object, with an expected closest approach of <10 solar radii (<0.046 au) by 2024. On board, the Integrated Science Investigation of the Sun instrument suite makes unprecedented in situ measurements of energetic particles in the near-Sun environment. The current low level of solar activity offers a prime opportunity to measure cosmic rays closer to the Sun than ever before. We present the first observations of anomalous cosmic rays in to 36 solar radii (0.166 au), focusing specifically on helium. Our results indicate a strong radial intensity gradient of ~25 ± 5%/au over energies of ~4 to ~45 MeV/nuc. These values are larger than prior observations, further out in the heliosphere, and come at a unique time in our understanding and modeling of particle transport and acceleration, particularly as both Voyagers have crossed the heliopause and IBEX has accumulated a full solar cycle of observations. Thus, continued measurements of cosmic rays by Parker Solar Probe will play a critical role in linking past observations with our present knowledge and significantly advancing our understanding of cosmic ray transport in the heliosphere.

Additional Information

© 2021. The American Astronomical Society. Received 2021 February 2; revised 2021 March 2; accepted 2021 March 3; published 2021 May 13. This work was supported as a part of the Integrated Science Investigation of the Sun on NASA's Parker Solar Probe mission, under contract NNN06AA01C. The IS⊙IS 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 SOHO/EPHIN team at Christian-Albrechts-Universität zu Kiel for making their data publicly available and Patrick Kühl and Bernd Heber for their guidance as well as their thorough documentation of the level 3 data product. We also gratefully acknowledge the 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 during EPI-Hi's calibration and testing. Parker Solar Probe was designed, built, and is now operated by the Johns Hopkins 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 the Parker Solar Probe mission. We thank all the scientists and engineers who have worked hard to make PSP a successful mission.

Attached Files

Published - Rankin_2021_ApJ_912_139.pdf

Files

Rankin_2021_ApJ_912_139.pdf
Files (1.5 MB)
Name Size Download all
md5:ae9200772aa0e1a26ce03d4b5de4eaa1
1.5 MB Preview Download

Additional details

Created:
August 22, 2023
Modified:
October 23, 2023