Shock-drift accelerated electrons and n-distribution

Astronomical Institute of the Czech Academy of Sciences, Fričova 258, 251 65 Ondřejov, Czech Republic
e-mail: vandas@asu.cas.cz

Received: 13 August 2015
Accepted: 9 May 2016

Abstract

Aims. By analyzing soft X-ray spectra observed during the impulsive phase of several solar flares, the n-distribution function of superthermal electrons has been detected. In the paper we try to answer the question of whether electrons with this type of distribution function can be produced in a shock, e.g. in a flare termination shock.

Methods. We use analytical and numerical methods to compute distribution functions of electrons accelerated by a shock.

Results. We analytically derive the distribution functions of reflected electrons at quasi-perpendicular shocks. We also consider the influence of the electrostatic cross-shock potential, shock curvature, and the role of the upstream seed population on these distributions. The computed distributions are compared with the n-distributions. We found that a high-energy part of the distribution of electrons reflected at a quasi-perpendicular shock can be very well fitted by the n-distribution in all the cases we studied. This provides a chance to detect the flare termination shock.