Inference of heating properties from "hot" non-flaring plasmas in active region cores. II. nanoflare trains

Abstract

Despite its prediction over two decades ago, the detection of faint, high-temperature (\hot") emission due to nano are heating in non- aring active region cores has proved challenging. Using an e cient two- uid hydrodynamic model, this paper investigates the properties of the emission expected from repeating nano ares (a nano are train) of varying frequency as well as the separate heating of electrons and ions. If the emission measure distribution (EM( T )) peaks at T = T m , we nd that EM( T m ) is independent of details of the nano are train, and EM( T ) above and below T m re ects di erent aspects of the heating. Below T m the main in uence is the relationship of the waiting time between successive nano ares to the nano are energy. Above T m power-law nano are distributions lead to an extensive plasma population not present in a monoenergetic train. Furthermore, in some cases characteristic features are present in EM( T ). Such details may be detectable given adequate spectral resolution and a good knowledge of the relevant atomic physics. In the absence of such resolution we propose some metrics that can be used to infer the presence of \hot" plasma.