Abstract
We report on the source of {>},300~mbox{MeV} protons during the SOL2014-09-01 sustained gamma-ray emission (SGRE) event based on multi-wavelength data from a wide array of space- and ground-based instruments. Based on the eruption geometry we provide concrete explanation for the spatially and temporally extended gamma -ray emission from the eruption. We show that the associated flux rope is of low inclination (roughly oriented in the east–west direction), which enables the associated shock to extend to the frontside. We compare the centroid of the SGRE source with the location of the flux rope’s leg to infer that the high-energy protons must be precipitating between the flux rope leg and the shock front. The durations of the SOL2014-09-01 SGRE event and the type II radio burst agree with the linear relationship between these parameters obtained for other SGRE events with duration geq 3~mbox{hrs}. The fluence spectrum of the SEP event is very hard, indicating the presence of high-energy (GeV) particles in this event. This is further confirmed by the presence of an energetic coronal mass ejection with a speed {>},2000~mbox{km},mbox{s}^{-1}, similar to those in ground level enhancement (GLE) events. The type II radio burst had emission components from metric to kilometric wavelengths as in events associated with GLE events. All these factors indicate that the high-energy particles from the shock were in sufficient numbers needed for the production of gamma -rays via neutral pion decay.
Highlights
Gamma-ray events temporally extended beyond the impulsive phase of solar flares were first reported by Forrest et al (1985) using the Solar Maximum Mission’s Gamma Ray Spectrometer (SMM/GRS) data
We report on the source of > 300 MeV protons during the SOL2014-09-01 sustained gamma-ray emission (SGRE) event based on multi-wavelength data from a wide array of space- and ground-based instruments
The SGRE peak occurred after the impulsive phase of the flare as revealed by the hard X-ray emission observed by the High Energy Neutron Detector (HEND) of the Gamma-ray Spectrometer onboard the Mars Odyssey mission
Summary
Gamma-ray events temporally extended beyond the impulsive phase of solar flares were first reported by Forrest et al (1985) using the Solar Maximum Mission’s Gamma Ray Spectrometer (SMM/GRS) data. The Gamma-ray burst experiment (PHEBUS) on board the GRANAT mission observed extended-phase emission at energies > 10 MeV (Talon et al, 1993; Vilmer et al, 2003). Using data from Gamma-1 telescope, Akimov et al (1991) reported on the 1991 June 15 event with the extended phase γ -ray emission lasting for more than 2 hr. Based on data from the Energetic Gamma Ray Experiment Telescope (EGRET) on board the Compton Gamma Ray Observatory (CGRO), Kanbach et al (1993) reported on another event with a duration exceeding 8 hr. As pointed out by Ryan (2000), the definition of the long-duration γ -ray events has been imprecise: the term “longduration gamma-ray flare (LDGRF)” refers to the γ -rays as flare, the flare is gone long before the end of the γ -ray events
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