Observation of solar high energy gamma and X-ray emission and solar energetic particles

TL;DR

This study analyzes 18 solar flares with high-energy gamma-ray emissions, revealing different acceleration processes for protons and electrons and showing that not all accelerated protons escape into space.

Contribution

It provides new insights into the relationship between high-energy gamma-ray emissions and particle acceleration mechanisms in solar flares.

Findings

Prolonged gamma-ray emissions can occur without concurrent >100 keV X-ray bursts.

Some high-energy gamma-ray events are not associated with SEP events at 1 AU.

Flares with prolonged gamma-ray emission show longer delays between temperature and emission measure peaks.

Abstract

We considered 18 solar flares observed between June 2010 and July 2012, in which high energy >100 MeV {\gamma}-emission was registered by the Large Area Telescope (LAT) aboard FermiGRO. We examined for these {\gamma}-events soft X-ray observations by GOES, hard X-ray observations by the Anti-Coincidence Shield of the SPectrometer aboard INTEGRAL (ACS SPI) and the Gamma-Ray burst Monitor (GBM) aboard FermiGRO. Hard X-ray and {\pi}0-decay {\gamma}-ray emissions are used as tracers of electron and proton acceleration, respectively. Bursts of hard X-ray were observed by ACS SPI during impulsive phase of 13 events. Bursts of hard X-ray >100 keV were not found during time intervals, when prolonged hard {\gamma}-emission was registered by LAT/FermiGRO. Those events showing prolonged high-energy gamma-ray emission not accompanied by >100 keV hard X-ray emission are interpreted as an indication of either different acceleration processes for protons and electrons or as the presence of a proton population accelerated during the impulsive phase of the flare and subsequently trapped by some magnetic structure. In-situ energetic particle measurements by GOES and STEREO (High Energy Telescope, HET) shows that five of these {\gamma}-events were not accompanied by SEP events at 1 AU, even when multi-point measurements including STEREO are taken into account. Therefore accelerated protons are not always released into the heliosphere. A longer delay between the maximum temperature and the maximum emission measure characterises flares with prolonged high energy {\gamma}-emission and solar proton events.