Alec L. MacKinnon

Properties of Energetic Ions in the Solar Atmosphere from γ -Ray and Neutron Observations

Gamma-rays and neutrons are the only sources of information on energetic ions present during solar flares and on properties of these ions when they interact in the solar atmosphere. The production of γ-rays and neutrons results from convolution of the nuclear cross-sections with the ion distribution functions in the atmosphere. The observed γ-ray and neutron fluxes thus provide useful diagnostics for the properties of energetic ions, yielding strong constraints on acceleration mechanisms as well as properties of the interaction sites. The problem of ion transport between the accelerating and interaction sites must also be addressed to infer as much information as possible on the properties of the primary ion accelerator. In the last couple of decades, both theoretical and observational developments have led to substantial progress in understanding the origin of solar γ-rays and neutrons. This chapter reviews recent developments in the study of solar γ-rays and of solar neutrons at the time of the RHESSI era. The unprecedented quality of the RHESSI data reveals γ-ray line shapes for the first time and provides γ-ray images. Our previous understanding of the properties of energetic ions based on measurements from the former solar cycles is also summarized. The new results—obtained owing both to the gain in spectral resolution (both with RHESSI and with the non solar-dedicated INTEGRAL/SPI instrument) and to the pioneering imaging technique in the γ-ray domain—are presented in the context of this previous knowledge. Still open questions are emphasized in the last section of the chapter and future perspectives on this field are briefly discussed.

Compton backscattered and primary X-rays from solar flares: angle dependent Green's function correction for photospheric albedo

The observed hard X-ray (HXR) flux spectrum

Coronal γ-Ray Bremsstrahlung from Solar Flare-accelerated Electrons

I(\epsilon)

NUMERICAL SIMULATIONS OF CHROMOSPHERIC HARD X-RAY SOURCE SIZES IN SOLAR FLARES

from solar flares is a combination of primary bremsstrahlung photons

Calibration of the Fast Neutron Imaging Telescope (FNIT) Prototype Detector

I_{\rm P}(\epsilon)

Development of the fast neutron imaging telescope

with a spectrally modified component from photospheric Compton backscatter of downward primary emission. The latter can be significant, distorting or hiding the true features of the primary spectrum which are key diagnostics for acceleration and propagation of high energy electrons and of their energy budget. For the first time in solar physics, we use a Greens function approach to the backscatter spectral deconvolution problem, constructing a Greens matrix including photoelectric absorption. This approach allows spectrum-independent extraction of the primary spectrum for several HXR flares observed by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). We show that the observed and primary spectra differ very substantially for flares with hard spectra close to the disk centre. We show in particular that the energy dependent photon spectral index

Charge-exchange Limits on Low-energy α-particle Fluxes in Solar Flares

\gamma (\epsilon)=-{\rm d} \log I/{\rm d} \log \epsilon

Inverse Compton X-rays from relativistic flare electrons and positrons

is very different for

Imaging solar neutrons below 10 MeV in the inner heliosphere

I_{\rm P}(\epsilon)

Recent Progress in Understanding Energy Conversion and Particle Acceleration in the Solar Corona

and for