CaltechAUTHORS
  A Caltech Library Service

Shock Geometry and Spectral Breaks in Large SEP Events

Li, G. and Zank, G. P. and Verkhoglyadova, Olga and Mewaldt, R. A. and Cohen, C. M. S. and Mason, G. M. and Desai, M. I. (2009) Shock Geometry and Spectral Breaks in Large SEP Events. Astrophysical Journal, 702 (2). pp. 998-1004. ISSN 0004-637X. http://resolver.caltech.edu/CaltechAUTHORS:20090917-150452855

[img]
Preview
PDF - Published Version
See Usage Policy.

272Kb

Use this Persistent URL to link to this item: http://resolver.caltech.edu/CaltechAUTHORS:20090917-150452855

Abstract

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 m_p . 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 κ ⊥. 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.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1088/0004-637X/702/2/998DOIArticle
http://www.iop.org/EJ/abstract/0004-637X/702/2/998/PublisherArticle
ORCID:
AuthorORCID
Cohen, C. M. S.0000-0002-0978-8127
Mason, G. M.0000-0003-2169-9618
Additional Information:© 2009. The American Astronomical Society. Received 2009 February 1; accepted 2009 July 9; published 2009 August 18. This work is supported in part by NASA grants NNX06AC21G, NNH07ZDA001N-HGI and NNX07AL52A for G.L., O.V., and G.P.Z. at UAH; NNX06AC21G, NNX8AI11G, and NNX07AP69G for RAM and CMSC at Caltech; Caltech subcontract 44A-1081056 for G.M.M. at A.P.L., and NNH07ZDA001N-HGI for M.I.D. at SWRI. The authors acknowledge discussions with M.A. Lee and an anonymous referee for valuable comments. G.L. thanks Dr. Yan Wang for some very stimulating discussions.
Group:Space Radiation Laboratory
Funders:
Funding AgencyGrant Number
NASANNX06AC21G
NASANNH07ZDA001N-HGI
NASANNX07AL52A
NASANNX06AC21G
NASANNX8AI11G
NASANNX07AP69G
Caltech44A-1081056
Subject Keywords:acceleration of particles; Sun: coronal mass ejections (CMEs)
Issue or Number:2
Record Number:CaltechAUTHORS:20090917-150452855
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20090917-150452855
Official Citation:Shock Geometry and Spectral Breaks in Large SEP Events G. Li, G. P. Zank, Olga Verkhoglyadova, R. A. Mewaldt, C. M. S. Cohen, G. M. Mason, and M. I. Desai 2009 ApJ 702 998-1004 doi: 10.1088/0004-637X/702/2/998
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:15930
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:18 Sep 2009 23:00
Last Modified:11 Sep 2017 18:35

Repository Staff Only: item control page