Using Gamma‐Ray and Neutron Emission to Determine Solar Flare Accelerated Particle Spectra and Composition and the Conditions within the Flare Magnetic Loop

Abstract

The measurable quantities associated with -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 -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 À1 . 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.

Capability of the accelerated protons as the origin of white-light emission of solar flare

“…From Fig. 18 of Murphy et al [36], the 2.2 MeV yield ratio was estimated to be 10 −2 photons/sr for 100 MeV ions. From these data, we obtained a total ion energy-production rate of 1.6 × 10 28 erg/s.…”

“…Murphy et al [36] estimated the 2.2 MeV line yields per accelerated proton of given energy in Fig. 18 of their paper.…”

FERMIDETECTION OF γ-RAY EMISSION FROM THE M2 SOFT X-RAY FLARE ON 2010 JUNE 12

“…Ratios of these emissions therefore determine the relative numbers of accelerated ions in the associated energy ranges. We then obtain spectral indices across these energy ranges by comparing measured ratios with ratios from theoretical calculations (Murphy et al , 2005(Murphy et al , 2007 based on updated nuclear cross sections.…”

Estimation of the solar flare neutron worst‐case fluxes and fluences for missions traveling close to the Sun

“…Such a code was constructed by Lingenfelter [1987a, 1987b] and improved and updated by Hua et al [2002]. The consequences of varying the ion acceleration and transport parameters of this code were described in detail by Murphy et al [2007]. These codes predict angular distributions and energy spectra of the neutrons escaping from the solar atmosphere (see the above references for further details).…”

“…This method is based on the use of (1) an energy spectra of neutrons escaping from the Sun obtained from the parametric study of the model of Hua et al [2002] performed by Murphy et al [2007] but normalized to one of the largest 100 MeV neutron fluxes at the Sun as inferred by , (2) a working relationship between the flux of neutrons at the Sun and the peak soft X-ray flux of the associated solar flare, (3) an estimation of the number and peak flux of soft X-ray flares that may occur during the lifetime of the mission, and (4) the probability that the solar neutrons emitted by each flare reach the heliocentric distance of the spacecraft on each day of the mission.…”