engleski

Energy release rates along Hα flare ribbons and the location of HXR sources

Local reconnection and energy release rates for an X3.8 flare that occurred on 17 January, 2005 are derived. In particular, we distinguished between Hα flare ribbon segments that were accompanied by RHESSI hard X-ray (HXR) footpoints and those without HXRs. We find that the reconnection and energy release rates are not uniform along the flare ribbons but much larger at the locations where the HXR footpoints are observed. The difference is about two orders of magnitude in case of the energy release rates and one order of magnitude for the reconnection rates (with peak values up to 8 kV m− 1). These differences are enough to explain the different flare morphologies typically observed in HXRs (compact footpoints) and Hα /UV (extended ribbons) by the limited dynamic range of present HXR instruments. Our results are consistent with a scenario where the electrons are accelerated primarily along a certain subsystem of magnetic loops as outlined by the hard X-ray footpoints, and only a minor fraction (for the 17 January, 2005 flare estimated to about 1/15) goes into the large flare arcade outlined by the Hα ribbons and EUV postflare loops.

Sun flares; Sun magnetic fields; Sun X-rays; γ -rays

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