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The sites of chromospheric excitation during solar flares are marked byextended extreme ultraviolet ribbons and hard X-ray footpoints. The standardinterpretation is that these are the result of heating and bremsstrahlungemission from non-thermal electrons precipitating from the corona. We examinethis picture using multi-wavelength observations of the early phase of anM-class flare SOL2010-08-07T18:24. We aim to determine the properties of theheated plasma in the flare ribbons, and to understand the partition of thepower input into radiative and conductive losses. Using GOES, SDO/EVE, SDO/AIAand RHESSI we measure the temperature, emission measure and differentialemission measure of the flare ribbons, and deduce approximate density values.The non-thermal emission measure, and the collisional thick target energy inputto the ribbons are obtained from RHESSI using standard methods. We deduce theexistence 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 averagecolumn emission measure of this hot component is a few times 10^28/cm^5, and wecan calculate that its predicted conductive losses dominate its measuredradiative losses. If the power input to the hot ribbon plasma is due tocollisional energy deposition by an electron beam from the corona then alow-energy cutoff of around 5 keV is necessary to balance the conductivelosses, implying a very large electron energy content. Independent of thestandard collisional thick-target electron beam interpretation, the observednon-thermal X-rays can be provided if one electron in 10^3 - 10^4 in the 10 MK(1 keV) ribbon plasma has an energy above 10 keV. We speculate that this couldarise if a non-thermal tail is generated in the ribbon plasma which is beingheated by other means, for example by waves or turbulence.

Flare Ribbon Energetics in the Early Phase of an SDO Flare