Charge-exchange limits on low-energy α-particle fluxes in solar flares

Hudson, H.S. , Fletcher, L. , MacKinnon, A.L. and Woods, T.N. (2012) Charge-exchange limits on low-energy α-particle fluxes in solar flares. Astrophysical Journal, 752(2), p. 84. (doi: 10.1088/0004-637X/752/2/84)

Abstract

This paper reports on a search for flare emission via charge-exchange radiation in the wings of the Lyα line of He II at 304 Å, as originally suggested for hydrogen by Orrall and Zirker. Via this mechanism a primary α particle that penetrates into the neutral chromosphere can pick up an atomic electron and emit in the He II bound-bound spectrum before it stops. The Extreme-ultraviolet Variability Experiment on board the Solar Dynamics Observatory gives us our first chance to search for this effect systematically. The Orrall-Zirker mechanism has great importance for flare physics because of the essential roles that particle acceleration plays; this mechanism is one of the few proposed that would allow remote sensing of primary accelerated particles below a few MeV nucleon^–1. We study 10 events in total, including the γ-ray events SOL2010-06-12 (M2.0) and SOL2011-02-24 (M3.5) (the latter a limb flare), seven X-class flares, and one prominent M-class event that produced solar energetic particles. The absence of charge-exchange line wings may point to a need for more complete theoretical work. Some of the events do have broadband signatures, which could correspond to continua from other origins, but these do not have the spectral signatures expected from the Orrall-Zirker mechanism.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Fletcher, Professor Lyndsay and Hudson, Dr Hugh and MacKinnon, Dr Alexander
• Authors: Hudson, H.S., Fletcher, L., MacKinnon, A.L., and Woods, T.N.
• College/School: College of Science and Engineering > School of Physics and Astronomy; College of Social Sciences > School of Education > Interdisciplinary Science Education Technologies and Learning
• Journal Name: Astrophysical Journal
• ISSN: 0004-637X
• ISSN (Online): 1538-4357
• Published Online: 30 May 2012