Shock Geometry and Spectral Breaks in Large SEP Events

Details Shock Geometry and Spectral Breaks in Large SEP Events Shock Geometry and Spectral Breaks in Large SEP Events

Sep 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009apj...702..998l&link_type=abstract

The Astrophysical Journal, Volume 702, Issue 2, pp. 998-1004 (2009).

Astronomy and Astrophysics

Astronomy

4

Acceleration Of Particles, Sun: Coronal Mass Ejections: Cmes

Scientific paper

Solar energetic particle (SEP) events are traditionally classified as "impulsive" or "gradual." It is now widely accepted that in gradual SEP events, particles are accelerated at coronal mass ejection-driven (CME-driven) shocks. In many of these large SEP events, particle spectra exhibit double power law or exponential rollover features, with the break energy or rollover energy ordered as (Q/A)α, with Q being the ion charge in e and A the ion mass in units of proton mass mp . This Q/A dependence of the spectral breaks provides an opportunity to study the underlying acceleration mechanism. In this paper, we examine how the Q/A dependence may depend on shock geometry. Using the nonlinear guiding center theory, we show that α ~ 1/5 for a quasi-perpendicular shock. Such a weak Q/A dependence is in contrast to the quasi-parallel shock case where α can reach 2. This difference in α reflects the difference of the underlying parallel and perpendicular diffusion coefficients κ|| and κbottom. We also examine the Q/A dependence of the break energy for the most general oblique shock case. Our analysis offers a possible way to remotely examine the geometry of a CME-driven shock when it is close to the Sun, where the acceleration of particle to high energies occurs.

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