High-energy gamma-ray emission from solar flares: Constraining the accelerated proton spectrum

Alexander, David; Dunphy, P. P.; MacKinnon, A. L.

doi:10.1007/bf00654088

Cited by 14 publications

(15 citation statements)

References 18 publications

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“…This was first seen with the SMM/GRS instrument in the flare of 3 June, 1982 (Forrest et al 1985), and deduction of the accelerated ion distribution to high energies followed (Murphy et al 1987). Alexander et al (1994) spectral feature seen in two other SMM flares, using it to discuss in a parametric way the relationship between the accelerated proton distribution at 10-100 MeV, and at >300 MeV. More recently, Dunphy et al (1999) estimated the accelerated proton spectra for the flare of 11 June, 1991 using CGRO/EGRET observations of γ-ray emissions in the 1 to 140 MeV range.…”

Section: Introductionmentioning

confidence: 93%

“…For photon production via π 0 decay resulting from p-p and p-α interactions, we follow Alexander et al (1994), who in turn mostly followed the approach of Dermer (1986a) and Murphy et al (1987). In this work we also evaluate the contribution from α-p interactions, noting that collisions of α's with other α's, and heavier nuclei, will add only a few percent to the total photon yield (Murphy et al 1987).…”

Section: Pion Decay Radiationmentioning

confidence: 99%

“…With this assumption, p-α and α-p reactions produce the same photon yield, at the same test particle energy (in MeV per nucleon). We also extend the work of Alexander et al (1994) by including the continuum resulting from bremsstrahlung and annihilation in flight of π + decay positrons (the contribution of π − decay electrons to the total gamma-ray fluence is at the 1% levelMurphy et al 1987 -so we neglect it). The production rate and energy distribution of π + is calculated similarly to Alexander et al using measured cross-sections for π + production, and isobar and scaling models for the π + energy distribution (Dermer 1986b).…”

Section: Pion Decay Radiationmentioning

confidence: 99%

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High energy particles accelerated during the large solar flare of 1990 May 24: X/γ-ray observations

Vilmer

MacKinnon

Trottet

et al. 2003

A&A

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Abstract. The PHEBUS experiment aboard GRANAT observed γ-ray line emission and γ-ray continuum above 10 MeV from the 24 May, 1990 solar flare. Observations and interpretation of the high-energy continuum have been discussed previously. Here we re-examine these, combining the PHEBUS observations above 10 MeV with calculations of the pion decay continuum to quantitatively constrain the accelerated ion energy distribution at energies above 300 MeV. The uncertainty in the determination of the level of the primary electron bremsstrahlung as well as the lack of measurements on the γ-ray emission above 100 MeV combine to allow rather a wide range of energy distribution parameters (in terms of the number of protons above 30 MeV, the spectral index of the proton distribution and the high energy cut-off of the energetic protons). Nevertheless we are able to rule out some combinations of these parameters. Using the additional information provided by the γ-ray line observations we discuss whether it is possible to construct a consistent picture of the ions which are accelerated in a wide energy range during this flare. Our findings are discussed with respect to previous works on the spectrum of energetic protons in the 10 MeV to GeV energy range.

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Section: Introductionmentioning

confidence: 93%

Section: Pion Decay Radiationmentioning

confidence: 99%

Section: Pion Decay Radiationmentioning

confidence: 99%

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High energy particles accelerated during the large solar flare of 1990 May 24: X/γ-ray observations

Vilmer

MacKinnon

Trottet

et al. 2003

A&A

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“…To explain the appearance of these lines it is necessary to accept that 10 33 protons are accelerated up to energies >30 MeV (Ramaty 1986). These same observations give evidence, apparently, for the existence of a cut-off in the proton spectrum beyond 700 MeV (Alexander et al 1994).…”

Section: Accelerated Particles In Impulsive Solar Flaresmentioning

confidence: 53%

Physical Processes During Impulsive Solar and Stellar Flares

Katsova

Livshits

1995

International Astronomical Union Colloquium

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Investigations of impulsive flares on both the Sun and red dwarf stais during more than 30 years allow us to arrive at quite definite conclusions. Here we will consider impulsive events; on the Sun the impulsive phase of a flare is observed as a hard X-ray burst with the emission of photons with energies E > 30 keV up to the γ-ray range. At the same time microwave radio bursts, and sometimes UV and optical continuum bursts are registered. Typical durations of these processes are ∼l-3 min. In this time interval other kinds of flare emission like soft X-ray (2-10 keV) emission, meter radio bursts and Balmer line emission begin to rise, but their maxima occur later on, in the gradual (thermal) phase of the flare.Impulsive stellar flares are often observed as a significant increase in optical continuum, especially in the U-band, of similar duration (1-3 min), and this time interval is, like in the solar case, the rise phase of the soft X-ray emission.Modern observations demonstrate that both the impulsive phase of a flare or an impulsive flare develops in low-lying loops. Earlier only indirect evidence existed in optical and radio data. Recently, however, the heights of the hard X-ray sources in impulsive solar events were determined directly from YOHKOH’s HXT (Kosugi 1994, Masuda 1994) (Fig. 1a). Statistically, the height of the hard X-ray source in the 14-23 keV range is 9700 ± 2000 km above the photosphere, and this height reduces to 6500 km in the 53-93 keV range. Besides two hard X-ray sources in the loop footpoints, a third hard X-ray source exists at the top of the loop at least in some cases. The authors of this experiment suppose that the appearance of this loop-top source is due to reconnection in the impulsive phase. Note that the reconnection begins close to the apex of the loop, when this loop is filled by hot plasma that evaporated from both footpoints.

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“…Assuming a spectral shape for the energetic ions (either a Bessel function or a power law), number and spectra of energetic protons were estimated for both the impulsive and the extended phase of the first detected event (1980 Jun 21) and showed that the proton spectrum was steeper in the impulsive phase than in the later, so-called 'extended' phase. This evolution of the ion spectrum in the extended phase was confirmed by further observations such as the ones of the 1991 Jun 11 event by CGRO/EGRET (Dunphy et al 1999).Quantitative analysis of several events with significant pion production has been performed providing information on the ion energy spectrum above 300 MeV/nucleon and allowing a comparison of this spectrum with the one deduced at lower energies from -ray line spectroscopy (see, e.g., Alexander et al 1994;Dunphy et al 1999;Kocharov et al 1994Kocharov et al , 1998 Vilmer et al 2003). These comparisons have shown that the ion energy distribution does not have a simple power-law form from the -ray line producing energy domain (1-10 MeV) to the pion-producing energy domain (>300 MeV/nucleon).…”

mentioning

confidence: 56%

X-Ray, Radio and SEP Observations of Relativistic Gamma-Ray Events

Klein¹,

Tziotziou²,

Zucca³

et al. 2017

Astrophysics and Space Science Library

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The rather frequent occurrence, and sometimes long duration, ofray events at photon energies above 100 MeV challenges our understanding of particle acceleration processes at the Sun. The emission is ascribed to pion-decay photons due to protons with energies above 300 MeV. We study the X-ray and radio emissions and the solar energetic particles (SEPs) in space for a set of 25 Fermi -ray events. They are accompanied by strong SEP events, including, in most cases where the parent activity is well-connected, protons above 300 MeV. Signatures of energetic electron acceleration in the corona accompany the impulsive and early post-impulsive -ray emission. -ray emission lasting several hours accompanies in general the decay phase of long-lasting soft X-ray bursts and decametric-tokilometric type II bursts. We discuss the impact of these results on the origin of the -ray events. IntroductionThe advent of the Fermi mission showed that the Sun is an occasional, but unexpectedly frequent, emitter of -ray photons above 100 MeV. These are understood to be produced by pion decays in nuclear interactions involving protons or He-nuclei at energies above 300 MeV/nucleon. One did not expect that the Sun was able to accelerate relativistic protons and nuclei even in seemingly modest flares. These particles are rarely detected in space (<1 event per year). Furthermore, the duration, several hours, of some -ray events is much longer than that of hard X-ray signatures of electron acceleration in the impulsive flare phase.The question of how the -ray emission is related to other signatures of particle acceleration and energy release in the corona is crucial to understanding the origin of the high-energy protons. It might also be expected that such high-energy populations interacting at the Sun are accompanied by particularly energetic solar energetic particle (SEP) events. This chapter is based on 25 events. The Fermi/LAT temporal data were made available to the HESPERIA project by G. Share prior to their publication in a comprehensive paper ). The present chapter introduces the relevant process of emission and pre-Fermi observations of piondecay -rays (Sect. 8.2), and gives an overview of the Fermi/LAT observations (Sect. 8.3). Section 8.3 was prepared by Gerald Share and Ron Murphy. Related X-ray and radio observations and associated SEP events are presented in Sects. 8.4 and 8.5, respectively. Preliminary conclusions on the interpretation of the -ray events are in Sect. 8.6. Theory and Early Observations of Gamma-Ray Emission at Photon Energies >60 MeVOn 1982 Jun 3 the gamma-ray spectrometer on the Solar Maximum Mission satellite observed emission from 0.3 to 100 MeV from a X8.0 GOES-class flare (Forrest et al. 1986). The impulsive flare lasted about 1 min and was followed by a distinct harder emission phase that peaked in about 1 min and lasted for over 15 min. The energy spectrum of this sustained emission displayed a characteristic hump at photon energies above 60 MeV (Fig. 8.1a), which appeared to be consistent with th...

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High-energy gamma-ray emission from solar flares: Constraining the accelerated proton spectrum

Cited by 14 publications

References 18 publications

High energy particles accelerated during the large solar flare of 1990 May 24: X/γ-ray observations

High energy particles accelerated during the large solar flare of 1990 May 24: X/γ-ray observations

Physical Processes During Impulsive Solar and Stellar Flares

X-Ray, Radio and SEP Observations of Relativistic Gamma-Ray Events

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