The Relationship between Long-Duration Gamma-Ray Flares and Solar Cosmic Rays

TL;DR

This paper explores the connection between long-duration solar gamma-ray flares and solar cosmic rays, analyzing their features, origins, and the challenges in identifying their solar structures using EUV imagery.

Contribution

It provides a detailed analysis of long-duration gamma-ray flares, highlighting their characteristics, associations with solar energetic particles, and proposing a solution to their unclear solar origin.

Findings

Gamma-ray flares have flat spectra above 100 keV and are associated with CMEs.

These flares are linked to high-energy ions producing pion decay gamma-rays.

The origin of gamma-ray production remains elusive despite EUV imagery.

Abstract

A characteristic pattern of solar hard X-ray emission, first identified in SOL1969-03-30 by Frost & Dennis (1971), turns out to have a close association with the prolonged high-energy gamma-ray emission originally observed by Forrest et al. (1985). This identification has become clear via the observations of long-duration gamma-ray flares by the Fermi/LAT experiment, for example in the event SOL2014-09-01. The distinctive features of these events include flat hard X-ray spectra extending well above 100 keV, a characteristic pattern of time development, low-frequency gyrosynchrotron peaks, CME association, and gamma-rays identifiable with pion decay originating in GeV ions. The identification of these events with otherwise known solar structures nevertheless remains elusive, in spite of the wealth of EUV imagery available from SDO/AIA. The quandary is that these events have a clear association with SEPs in the high corona, and yet the gamma-ray production implicates the photosphere itself, despite the strong mirror force that should focus the particles \textit{away} from the Sun We discuss the morphology of these phenomena and propose a solution to this problem.