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Anomalous Cosmic-Ray Oxygen Observations into 0.1 au

Rankin, J. S. and McComas, D. J. and Leske, R. A. and Christian, E. R. and Cohen, C. M. S. and Cummings, A. C. and Joyce, C. J. and Labrador, A. W. and Mewaldt, R. A. and Schwadron, N. A. and Stone, E. C. and Strauss, R. D. and Wiedenbeck, M. E. (2022) Anomalous Cosmic-Ray Oxygen Observations into 0.1 au. Astrophysical Journal, 925 (1). Art. No. 9. ISSN 0004-637X. doi:10.3847/1538-4357/ac348f.

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The Integrated Science Investigation of the Sun instrument suite onboard NASA's Parker Solar Probe mission continues to measure solar energetic particles and cosmic rays closer to the Sun than ever before. Here, we present the first observations of cosmic rays into 0.1 au (21.5 solar radii), focusing specifically on oxygen from ∼2018.7 to ∼2021.2. Our energy spectra reveal an anomalous cosmic-ray-dominated profile that is comparable to that at 1 au, across multiple solar cycle minima. The galactic cosmic-ray-dominated component is similar to that of the previous solar minimum (Solar Cycle 24/25 compared to 23/24) but elevated compared to the past (Solar Cycle 20/21). The findings are generally consistent with the current trend of unusually weak solar modulation that originated during the previous solar minimum and continues today. We also find a strong radial intensity gradient: 49.4 ± 8.0% au⁻¹ from 0.1 to 0.94 au, for energies of 6.9–27 MeV nuc⁻¹. This value agrees with that measured by Helios nearly 45 yr ago from 0.3 to 1.0 au (48% ± 12% au⁻¹; 9–29 MeV nuc⁻¹) and is larger than predicted by models. The large anomalous cosmic-ray gradients observed close to the Sun by the Parker Solar Probe Integrated Science Investigation of the Sun instrument suite found here suggest that intermediate-scale variations in the magnetic field's structure strongly influence cosmic-ray drifts, well inside 1 au.

Item Type:Article
Related URLs:
URLURL TypeDescription ItemIS⊙IS data and visualization tools ItemNASA Space Physics Data Facility Paper
Rankin, J. S.0000-0002-8111-1444
McComas, D. J.0000-0001-6160-1158
Leske, R. A.0000-0002-0156-2414
Christian, E. R.0000-0003-2134-3937
Cohen, C. M. S.0000-0002-0978-8127
Cummings, A. C.0000-0002-3840-7696
Joyce, C. J.0000-0002-3841-5020
Labrador, A. W.0000-0001-9178-5349
Mewaldt, R. A.0000-0003-2178-9111
Schwadron, N. A.0000-0002-3737-9283
Stone, E. C.0000-0002-2010-5462
Strauss, R. D.0000-0002-0205-0808
Wiedenbeck, M. E.0000-0002-2825-3128
Additional Information:© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2021 September 16; revised 2021 October 23; accepted 2021 October 26; published 2022 January 20. 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; data are also available via the NASA Space Physics Data Facility ( 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. We also 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.
Group:Astronomy Department, Space Radiation Laboratory
Funding AgencyGrant Number
Subject Keywords:Galactic cosmic rays; Cosmic rays; Solar cycle; Oxygen burning; Solar magnetic fields; Solar physics; Solar wind; Particle astrophysics; Space plasmas; Heliosphere; Quiet sun; Interplanetary turbulence
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Galactic cosmic rays (567); Cosmic rays (329); Solar cycle (1487); Oxygen burning (1193); Solar magnetic fields (1503); Solar physics (1476); Solar wind (1534); Particle astrophysics (96); Space plasmas (1544); Helios
Record Number:CaltechAUTHORS:20220121-870753000
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Official Citation:J. S. Rankin et al 2022 ApJ 925 9
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:113056
Deposited By: George Porter
Deposited On:21 Jan 2022 23:27
Last Modified:21 Jan 2022 23:27

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