Radio, Hard X-Ray, and Gamma-Ray Emissions Associated with a Far-Side Solar Event

Abstract

The SOL2014-09-01 far-side solar eruptive event produced hard electromagnetic and radio emissions observed with detectors at near-Earth vantage points. Especially challenging was a long-duration >100 MeV $\gamma$-ray burst probably produced by accelerated protons exceeding 300 MeV. This observation raised a question of how high-energy protons could reach the Earth-facing solar surface. Some preceding studies discussed a scenario in which protons accelerated by a CME-driven shock high in the corona return to the solar surface. We continue with the analysis of this challenging event, involving radio images from the Nançay Radioheliograph and hard X-ray data from the High Energy Neutron Detector (HEND) of the Gamma-Ray Spectrometer onboard the Mars Odyssey space observatory located near Mars. HEND recorded unocculted flare emission. The results indicate that the emissions observed from the Earth's direction were generated by flare-accelerated electrons and protons trapped in static long coronal loops. Their reacceleration is possible in these loops by a shock wave, which was excited by the eruption, being initially not CME-driven. The results highlight the ways to address remaining questions.

arXiv comment36 pages, 11 figures. For associated movie file, see http://ssrt.iszf.irk.ru/~grechnev/papers/2014-09-01/ Accepted for publication in Solar Physics

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• Source of Energetic Protons in the 2014 September 1 Sustained Gamma-ray Emission Event
• The coupling of an EUV coronal wave and ion acceleration in a Fermi-LAT behind-the-limb solar flare
• The Common Origin of High-energy Protons in Solar Energetic Particle Events and Sustained Gamma-ray Emission from the Sun
• Energetic Proton Back-Precipitation onto the Solar Atmosphere in Relation to Long-Duration Gamma-Ray Flares
• Evidence for flare-accelerated particles in large scale loops in the behind-the-limb gamma-ray solar flare of September 29, 2022
• Multiwavelength Stereoscopic Observation of the May 1, 2013 Solar Flare and CME
• On the origin of hard X-ray emissions from the behind-the-limb flare on 2014 September 1
• The 2024 July 16 Solar Event: A Challenge To The Coronal Mass Ejection Origin Of Long-Duration Gamma-Ray Flares