Using gamma-ray and neutron emission to determine solar flare accelerated particle spectra and composition and the conditions within the flare magnetic loop

R. J. Murphy, Benzion Kozlovsky, G. H. Share, X. M. Hua, R. E. Lingenfelter

Research output: Contribution to journalArticlepeer-review

Abstract

The measurable quantities associated with γ-ray and neutron observations of solar flares are nuclear-deexcitation line shapes, shifts, fluences, and time histories; neutron capture and annihilation line fluences and time histories; and energy-dependent escaping neutron fluence and time history. A comprehensive understanding of these quantities requires a model for ion acceleration, transport, and interaction. In this paper we address transport and interaction using a magnetic loop model that includes energy losses due to Coulomb collisions, removal by nuclear reactions, magnetic mirroring in the convergent flux tube, and MHD pitch-angle scattering in the corona. The accelerated ions are assumed to have a given kinetic energy spectrum and composition. Each measurable quantity depends to varying degree on the parameters of the loop model and of the accelerated ions. We explore these dependences in detail and construct a self-consistent approach to the analysis of high-energy flare data that provides an optimum set of parameters with meaningful uncertainties. To illustrate this approach, the calculations are applied in a comprehensive analysis of the γ-ray and neutron observations of the 1991 June 4 solar flare obtained with OSSE on CGRO. We find that the loop model can account for these observations with physically reasonable values for the parameters. In addition, our analysis of the neutron data shows that the accelerated ion spectrum for this flare was not an unbroken power law but had to steepen sharply above ∼125 MeV nucleon-1. The paper also provides yields and yield ratios calculated with assumed abundances and spectral forms currently considered appropriate for solar flares. They can be used by other researchers analyzing high-energy solar flare data.

Original languageEnglish
Pages (from-to)167-194
Number of pages28
JournalAstrophysical Journal, Supplement Series
Volume168
Issue number1
DOIs
StatePublished - Jan 2007

Keywords

  • Acceleration of particles
  • Nuclear reactions, nucleosynthesis, abundances
  • Sun: X-rays, gamma rays
  • Sun: flares

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