On the Shock Source of Sustained Gamma-Ray Emission from the Sun

N Gopalswamy,S Yashiro,H Xie,A Lara,P Mäkelä,S Akiyama

doi:10.1088/1742-6596/1332/1/012004

Abstract

It has recently been shown that the spatially and temporally extended γ-ray emission in solar eruptions are caused by >300 MeV protons precipitating on the Sun from shocks driven by coronal mass ejections (CMEs). The γ-rays result from the decay of neutral pions produced in the proton-proton interaction when the >300 MeV protons collide with those in the chromosphere. The evidence comes from the close correlation between the durations of the sustained gamma-ray emission (SGRE) and the associated interplanetary (IP) type II radio bursts. In this paper, we provide further evidence that support the idea that protons accelerated in IP shocks driven by CMEs propagate toward the Sun, precipitate in the chromosphere to produce the observed SGRE. We present the statistical properties of the SGRE events and the associated CMEs, flares, and type II radio bursts. It is found that the SGRE CMEs are similar to those associated with ground level enhancement events. The CME speed is well correlated with the SGRE fluence. High CME speed is an important requirement for the occurrence of SGRE, while the flare size is not. Based on these results, we present a schematic model illustrating the spatially and temporally extended nature of SGRE related to the CME flux rope-shock structure.

Highlights

Morrison [1] suggested that both continuum and line emissions in the γ-ray band are expected from cosmic sources due to processes such as bremsstrahlung, radiative decay of neutral pions, de-excitation of nuclei, and electron-positron annihilation
We examine the close connection among sustained gamma-ray emission (SGRE), type II radio bursts, and solar energetic particles (SEPs) events, all related to energetic coronal mass ejections (CMEs) that seem to be the key solar phenomenon of interest
Fermi/LAT SGRE Events In order to provide an overview of the SGRE events and the associated phenomena studied in this work, we have shown the 2012 January 23 event associated with a CME from NOAA active region (AR) 11402 located at N28W21

Summary

Introduction

Morrison [1] suggested that both continuum and line emissions in the γ-ray band are expected from cosmic sources due to processes such as bremsstrahlung, radiative decay of neutral pions, de-excitation of nuclei, and electron-positron annihilation. We examine the close connection among SGRE, type II radio bursts, and SEP events, all related to energetic CMEs that seem to be the key solar phenomenon of interest. The SGRE, flare, CME, SEP, and type II burst characteristics derived this way are listed in Table 1 for 19 Fermi/LAT SGRE events with duration >3 hr (from [13,31]).

Results

Conclusion