50 years of research on particle acceleration in the heliosphere

14th Annual International Astrophysics Conference: Linear and Nonlinear Particle Energization throughout the Heliosphere and Beyond

物理学;天文学

Fisk, L.A.^1

Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, 2455 Hayward St., Ann Arbor

MI

48109-2143, United States^1

关键词: Acceleration mechanisms;    Anomalous cosmic rays;    Diffusive shock accelerations;    Galactic cosmic rays;    Low-energy particles;    Orders of magnitude;    Particle acceleration;    Solar energetic particles;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/642/1/012009/pdf
DOI  :  10.1088/1742-6596/642/1/012009

学科分类：天文学(综合)

来源: IOP

【 摘 要 】

In 1965, and through the late 1960s, the heliosphere was considered to be a passive place, an impediment to the information on the galaxy contained in galactic cosmic ray observations, and on the Sun, from solar energetic particles. All this changed in the early 1970s with the discovery of the Anomalous Cosmic Rays (ACRs), and the subsequent acceptance that the ACRs are ionized interstellar neutral gas that is accelerated in the heliosphere by four orders of magnitude in energy. In the mid-1970s, Pioneer 10 & 11 observations provided direct evidence of acceleration. In 1977-78, diffusive shock acceleration was introduced, and subsequently developed in detail, providing compelling explanations for, e.g., the observed acceleration in co-rotating interaction regions, and a likely explanation for the acceleration of ACRs at the termination shock of the solar wind. In 2004 and 2008, the Voyagers crossed the termination shock, did not observe the acceleration of the ACRs, but did observe that low- energy particles, up to a few MeV/nucleon, had identical spectra downstream from the termination shock, a distribution function that is a power law in particle speed with a spectral index of -5. When Voyager 1 reached ∼120 AU, where the high-energy ACRs are at peak intensity, the ACR spectrum is also a -5 spectrum. Moreover, observations of suprathermal tails in the solar wind in the inner solar system have a -5 spectrum, often peaking downstream, but not at shocks. These observations led to the development of a new acceleration mechanism, the pump acceleration mechanism of Fisk & Gloeckler, which can account for all the observed -5 spectra.