Warm thick target solar<i>γ</i>-ray source revisited

MacKinnon, A. L.; Toner, M. P.

doi:10.1051/0004-6361:20030943

Cited by 6 publications

(2 citation statements)

References 41 publications

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“…Figure 7 shows the value of Λ ef f throughout the chromospheric portion of the C7 atmosphere of Avrett and Loeser (2003), for protons of energies 1, 10 and 100 MeV. The importance of retaining the energy-dependence of Λ has been emphasised elsewhere (MacKinnon and Toner, 2003). The variable degree of ionisation means that Λ ef f also depends strongly on position.…”

Section: Discussionmentioning

confidence: 99%

Origin of the 30 THz Emission Detected During the Solar Flare on 2012 March 13 at 17:20 UT

et al. 2015

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Solar observations in the infrared domain can bring important clues on the response of the low solar atmosphere to primary energy released during flares. At present the infrared continuum has been detected at 30 THz (10 µm) in only a few flares. SOL2012-03-13 , which is one of these flares, has been presented and discussed in Kaufmann et al. (2013). No firm conclusions were drawn on the origin of the mid-infrared radiation. In this work we present a detailed multi-frequency analysis of the SOL2012-03-13 event, including observations at radio millimeter and sub-millimeter wavelengths, in hard X-rays (HXR), gamma-rays (GR), Hα, and white-light. HXR/GR spectral analysis shows that SOL2012-03-13 is a GR line flare and allows estimating the numbers of and energy contents in electrons, protons and α particles produced during the flare. The energy spectrum of the electrons producing the HXR/GR continuum is consistent with a broken power-law with an energy break at ∼ 800 keV. It is shown that the high-energy part (above ∼ 800 keV) of this distribution is responsible for the high-frequency radio emission (> 20 GHz) time-independent models of the quiet and flare atmospheres, we find that most (∼80%) of the observed 30 THz radiation can be attributed to thermal freefree emission of an optically-thin source. Using the F2 flare atmospheric model (Machado et al., 1980) this thin source is found to be at temperatures T ∼ 8000 K and is located well above the minimum temperature region. We argue that the chromospheric heating, which results in 80 % of the 30 THz excess radiation, can be due to energy deposition by non-thermal flare accelerated electrons, protons and α particles. The remaining 20% of the 30 THz excess emission is found to be radiated from an optically-thick atmospheric layer at T ∼ 5000 K, below the temperature minimum region, where direct heating by non-thermal particles is insufficient to account for the observed infrared radiation.

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Section: Discussionmentioning

confidence: 99%

Origin of the 30 THz Emission Detected During the Solar Flare on 2012 March 13 at 17:20 UT

et al. 2015

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“…ii) FLUKA models the slowing down of ions assuming a neutral medium. The Coulomb logarithm may be significantly larger (typically by a factor of up to three) in an ionised medium (Hayakawa and Kitao, 1956;MacKinnon and Toner, 2003;Trottet et al, 2015). Most previous calculations of solar pion decay radiation employ neutral medium stopping rates, appropriate to the deep atmosphere (e.g.…”

Section: Discussionmentioning

confidence: 99%

FLUKA Simulations of Pion Decay Gamma-Radiation from Energetic Flare Ions

et al. 2020

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Gamma-ray continuum at $> 10 $ > 10 MeV photon energy yields information on $\gtrsim 0.2 $ ≳ 0.2 – 0.3 GeV/nucleon ions at the Sun. We use the general-purpose Monte Carlo code FLUktuierenden KAskade (FLUKA) to model the transport of ions injected into thick and thin target sources, the nuclear processes that give rise to pions and other secondaries and the escape of the resulting photons from the atmosphere. We give examples of photon spectra calculated with a range of different assumptions about the primary ion velocity distribution and the source region. We show that FLUKA gives results for pion decay photon emissivity in agreement with previous treatments. Through the directionality of secondary products, as well as Compton scattering and pair production of photons prior to escaping the Sun, the predicted spectrum depends significantly on the viewing angle. Details of the photon spectrum in the $\approx 100$ ≈ 100 MeV range may constrain the angular distribution of primary ions and the depths at which they interact. We display a set of thick-target spectra produced making various assumptions about the incident ion energy and angular distribution and the viewing angle. If ions are very strongly beamed downward, or ion energies do not extend much above 1 GeV/nucleon, the photon spectrum is highly insensitive to details of the ion distribution. Under the simplest assumptions, flares observed near disc centre should not display significant radiation above 1 GeV photon energy. We give an example application to Fermi Large Area Telescope data from the flare of 12 June 2010.

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Properties of Energetic Ions in the Solar Atmosphere from γ-Ray and Neutron Observations

Vilmer¹,

MacKinnon²,

Hurford³

2011

High-Energy Aspects of Solar Flares

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Gamma-rays and neutrons are the only sources of information on energetic ions present during solar flares and on properties of these ions when they interact in the solar atmosphere. The production of γ-rays and neutrons results from convolution of the nuclear cross-sections with the ion distribution functions in the atmosphere. The observed γ-ray and neutron fluxes thus provide useful diagnostics for the properties of energetic ions, yielding strong constraints on acceleration mechanisms as well as properties of the interaction sites. The problem of ion transport between the accelerating and interaction sites must also be addressed to infer as much information as possible on the properties of the primary ion accelerator. In the last couple of decades, both theoretical and observational developments have led to substantial progress in understanding the origin of solar γ-rays and neutrons. This chapter reviews recent developments in the study of solar γ-rays and of solar neutrons at the time of the RHESSI era. The unprecedented quality of the RHESSI data reveals γray line shapes for the first time and provides γ-ray images. Our previous understanding of the properties of energetic ions based on measurements from the former solar cycles is also summarized. The new results -obtained owing both to the gain in spectral resolution (both with RHESSI and with the non solar-dedicated INTEGRAL/SPI instrument) and to the pioneering imaging technique in the γ-ray domain -are presented in the context of this previous knowledge. Still open questions are emphasized in the last section of the chapter and future perspectives on this field are briefly discussed.

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Warm thick target solarγ-ray source revisited

Cited by 6 publications

References 41 publications

Origin of the 30 THz Emission Detected During the Solar Flare on 2012 March 13 at 17:20 UT

Origin of the 30 THz Emission Detected During the Solar Flare on 2012 March 13 at 17:20 UT

FLUKA Simulations of Pion Decay Gamma-Radiation from Energetic Flare Ions

Properties of Energetic Ions in the Solar Atmosphere from γ-Ray and Neutron Observations

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