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Application to Solar Flares

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Hard X-Ray Imaging of Solar Flares

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Abstract

In this chapter we apply the algorithms discussed in the previous chapters to selected solar flare events and discuss the physical implications of the results obtained. These investigations have a wide scope and include the following topics:

  • The number and physical nature of hard X-ray sources in flares;

  • Properties of the region in which the accelerated electrons are produced;

  • Energy loss processes affecting accelerated electrons;

  • Energetics of accelerated electrons and heated plasma and their contribution to the global energy budget of a solar eruptive event.

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Notes

  1. 1.

    Recall that 1 arcsecond (1′′) corresponds to ∼725 km on the Sun, when viewed from the Earth at a normal (i.e., 90∘) angle to the solar surface; a \(\sec \theta \) de-projection factor must be applied in calculating distances on the solar surface for sources at a heliocentric angle θ from disk center. The heliocentric angle for a source with coordinates (x, y) is given by \(\sin \theta = \sqrt {x^2 + y^2}/R\), where R ≃960 arcseconds is the solar radius as viewed from the Earth.

  2. 2.

    More recently, in a further series of papers summarized in [9], the results were presented of a comprehensive analysis of the global energetics of 399 solar M- and X-class flare events observed during the first 3.5 years of the Solar Dynamics Observatory (SDO) mission (2010–2013). The best effort was made to determine the magnetic, thermal, and nonthermal energies of each flare and the energies of the associated CMEs. The claim is made that this was “the first statistical study that establishes energy closure in solar flare-CME events,” meaning that the sum of all the flare and CME energies is (within uncertainties) equal to the dissipated magnetic energy. The nonthermal energies in flare-accelerated electrons were revised in [10], with an emphasis on using a consistent values of the low energy cutoff (cf. Eq. (1.27)) to the electron spectra, but the main conclusion concerning closure was not changed. However, [199] pointed out that there are “contradicting results on energy partition obtained by various recent studies.” These differences may be caused by changes in the thermal-nonthermal energy partition with flare strength. If this is the case, then the authors claim that “(a) an additional direct (i.e., non-beam) heating mechanism has to be present, and (b) considering that the bolometric emission originates mainly from deeper atmospheric layers, conduction or waves are required as additional energy transport mechanisms.

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Authors and Affiliations

  1. The MIDA Group, Dipartimento di Matematica, Università di Genova and CNR - SPIN Genova, Genova, Italy

    Michele Piana & Anna Maria Massone

  2. Department of Physics & Astronomy, Western Kentucky University, Bowling Green, KY, USA

    A. Gordon Emslie

  3. Solar Physics Laboratory, Code 671, Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD, USA

    Brian R. Dennis

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  1. Michele Piana
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Piana, M., Emslie, A.G., Massone, A.M., Dennis, B.R. (2022). Application to Solar Flares. In: Hard X-Ray Imaging of Solar Flares. Springer, Cham. https://doi.org/10.1007/978-3-030-87277-9_7

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  • DOI: https://doi.org/10.1007/978-3-030-87277-9_7

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  • Publisher Name: Springer, Cham

  • Print ISBN: 978-3-030-87276-2

  • Online ISBN: 978-3-030-87277-9

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