Remote Sensing of Gamma‐Ray Emission from Solar Energetic Proton Interactions with the Solar Wind

Abstract

The properties of solar energetic particles (SEPs) in solar flares are studied through remote imaging in the radio, hard X-ray, and -ray energy ranges. However, the heliospheric SEP populations are observed only in situ by satellite measurements, which drastically limits our understanding of their spatial and temporal variations. Can those SEP populations be remotely imaged, as are the solar SEPs? We consider two possibilities for detecting faint -ray emission from SEP interactions with solar wind (SW) ions. First, the 6.13 and 4.44 MeV -ray lines of 16 O and 12 C, respectively, produced by the interactions of the SEPs from a large low-energy (E < 30 MeV) gradual event are calculated and found to be far below a detectable level. Then the expected 0 -decay -ray emission is calculated for the intense ground-level event (GLE) of 2005 January 20 and compared with (1) the observed Galactic and extragalactic background and (2) the expected near-solar emission from inverse-Compton scattering of solar photons by cosmic-ray electrons and from Galactic cosmic-ray collisions with the solar atmosphere. It appears feasible to detect the 0 -decay emission from that event with a detector of the size of the Large Area Telescope on GLAST. Earlier 1982 and 1991 flare observations of long-duration (hours) 0 -decays were attributed to E > 300 MeV protons captured in strong coronal loops, but we suggest that the observed emission was due to SEP-SW collisions following shock acceleration on open field lines.

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

“…If that were the case, the ions might be expected to interact with ambient material in a more diffuse pattern, perhaps at some distance from the flare. This shows that the γ-ray emission does not result from the interaction of solar energetic particles with the solar wind as alternatively proposed by Kahler & Ragot (2008).…”

“…Also, it has not confirmed the SMMera suggestion that 2.223 MeV line emission might be produced over an extended region (Vestrand & Forrest 1993). The observations are also not consistent with a production of γ-rays through the interaction of solar energetic protons with the solar wind as examined by Kahler & Ragot (2008). We may look forward to further advances, both observational (e.g., with GRIPS; Shih et al 2009a), and theoretical, over the next few years.…”

Coronal Radiation Belts

“…Various mechanisms exist (e.g. Moskalenko et al 2006;Kahler & Ragot 2008), and both EGRET (Orlando & Strong 2008) asyet-unpublished Fermi results show a distinct source of high-energy γ rays from the solar direction. The particle environment of the corona itself may play a role in understanding this source and its relationship to solar-system background sources for Fermi observations.…”

Space Weather Prediction

“…The first investigation considered gamma-ray emission from high energy (E > 300 MeV) ion collisions with solar wind ions. This research effort found that such emission might be detected for very energetic SEP events [4,5]. Furthermore, a description of aSEP short-term warning model and its performance in preliminary evaluation was completed.…”