Footpoint versus loop-top hard X-ray emission sources in solar flares

Astronomical Institute, University of Wrocław, ul. Kopernika 11, 51–622 Wrocław, Poland e-mail: tomczak@astro.uni.wroc.pl

Received: 26 July 2006
Accepted: 5 September 2006

Abstract

Aims.The hard X-ray flux ratio of the footpoint sources to the loop-top source has been used to investigate non-thermal electron trapping and precipitation in solar flares.

Methods.Considering the mission-long Yohkoh Hard X-ray Telescope database, from which we selected 117 flares, we investigated a dependence of the ratio on flare loop parameters like height h and column depth N. We used non-thermal electron beams as a diagnostic tool for magnetic convergence.

Results.The ratio decreases with h which we interpret as an effect of converging field geometry. Two branches seen in the diagram suggest that in the solar corona two kinds of magnetic loops can exist: a more-converged ones that are more frequent (above 80%) and less-converged loops that are less frequent (below 20%). A lack of correlation between the ratio and N can be due to a more complex configuration of investigated events than seen in soft X-rays.

Conclusions.Obtained values of the magnetic mirror ratio are consistent with previous works and suggest a strongly nonpotential configuration. Further investigation including RHESSI data is needed to verify our results.