FLARE RIBBON ENERGETICS IN THE EARLY PHASE OF AN SDO FLARE

Journal Article · Wed Jul 10 00:00:00 EDT 2013 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/771/2/104· OSTI ID:22140154

Fletcher, L.; Hannah, I. G.; Hudson, H. S. ^[1]; Innes, D. E. ^[2]

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1. School of Physics and Astronomy, SUPA, University of Glasgow, Glasgow, G12 8QQ (United Kingdom)
2. Max Planck Institute for Solar System Research, Max-Planck-Strasse 2, D-37191 Katlenburg-Lindau (Germany)

The sites of chromospheric excitation during solar flares are marked by extended extreme ultraviolet ribbons and hard X-ray (HXR) footpoints. The standard interpretation is that these are the result of heating and bremsstrahlung emission from non-thermal electrons precipitating from the corona. We examine this picture using multi-wavelength observations of the early phase of an M-class flare SOL2010-08-07T18:24. We aim to determine the properties of the heated plasma in the flare ribbons, and to understand the partition of the power input into radiative and conductive losses. Using GOES, SDO/EVE, SDO/AIA, and RHESSI, we measure the temperature, emission measure (EM), and differential emission measure of the flare ribbons, and deduce approximate density values. The non-thermal EM, and the collisional thick target energy input to the ribbons are obtained from RHESSI using standard methods. We deduce the existence of a substantial amount of plasma at 10 MK in the flare ribbons, during the pre-impulsive and early-impulsive phase of the flare. The average column EM of this hot component is a few times 10{sup 28} cm{sup -5}, and we can calculate that its predicted conductive losses dominate its measured radiative losses. If the power input to the hot ribbon plasma is due to collisional energy deposition by an electron beam from the corona then a low-energy cutoff of {approx}5 keV is necessary to balance the conductive losses, implying a very large electron energy content. Independent of the standard collisional thick-target electron beam interpretation, the observed non-thermal X-rays can be provided if one electron in 10{sup 3}-10{sup 4} in the 10 MK (1 keV) ribbon plasma has an energy above 10 keV. We speculate that this could arise if a non-thermal tail is generated in the ribbon plasma which is being heated by other means, for example, by waves or turbulence.

• OSTI ID: 22140154
• Journal Information: Astrophysical Journal, Vol. 771, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
APPROXIMATIONS
BREMSSTRAHLUNG
CHROMOSPHERE
DENSITY
EMISSION
ENERGY ABSORPTION
ENERGY ACCOUNTING
ENERGY LOSSES
EXCITATION
EXTREME ULTRAVIOLET RADIATION
GAMMA RADIATION
GRAY ENERGY
HARD X RADIATION
KEV RANGE
PLASMA
PRECIPITATION
SOLAR FLARES
SUN
TURBULENCE
WAVELENGTHS