Inference of Heating Properties From “Hot” Non-Flaring Plasmas in Active Region Cores. I. Single Nanoflares

Abstract

The properties that are expected of "hot" non-flaring plasmas due to nanoflare heating in active regions are investigated using hydrodynamic modeling tools, including a two-fluid development of the Enthalpy Based Thermal Evolution of Loops code. Here we study a single nanoflare and show that while simple models predict an emission measure distribution extending well above 10 MK, which is consistent with cooling by thermal conduction, many other effects are likely to limit the existence and detectability of such plasmas. These include: differential heating between electrons and ions, ionization non-equilibrium, and for short nanoflares, the time taken for the coronal density to increase. The most useful temperature range to look for this plasma, often called the "smoking gun" of nanoflare heating, lies between 10 6.6 and 10 7 K. Signatures of the actual heating may be detectable in some instances.

Two-phase Heating in Flaring Loops

“…Thus EBTEL is expected to provide a good approximation at least in the long gradual phase of the flare. Other effects, e.g., how the spatial and temporal changes of the cross section (Klimchuk 2001;Mikić et al 2013) and the plasma composition (Phillips 2004;Barnes et al 2016) affect the hydrodynamic evolution of a loop/thread should be evaluated in the future study.…”

Small electron acceleration episodes in the solar corona

“…There is ample evidence for acceleration processes in the solar corona that result in nonthermal particle distributions. These include the radiative signatures and direct particle detections in large eruptive events that result in flares and coronal mass ejections (CMEs) (Zharkova et al 2011;Vilmer 2012;Aschwanden 2012;Miller et al 1997;Kontar et al 2011;Holman et al 2011;Aschwanden et al 2017). The underlying driver for such particle acceleration events is generally understood to be the excess energy stored in stressed magnetic fields that is released via the process of magnetic reconnection.…”

“…While this broad picture has been accepted for a while, it is only recently that observations have started to reveal some details (Kontar et al 2017) and simulations have started to establish the details of particle acceleration in reconnection regions (e.g., (Vlahos et al 2016;Arzner & Vlahos 2004;Dahlin et al 2015) and references therein). On the other hand, the possibility of small, ubiquitous reconnection events accelerating electrons and giving rise to the so-called nanoflares (Parker 1988) has gained considerable momentum as a candidate for coronal heating (e.g., (Klimchuk 2015;Barnes et al 2016) and references therein).Recent simulations have demonstrated the spontaneous development of current sheets with a high filling factor, even away from magnetic nulls ((Kumar et al 2015;Kumar & Bhattacharyya 2016)); these current sheets can serve as potential E-mail: tomin.james@students.iiserpune.ac.in sites for small electron acceleration events. However, since these nanoflares are very small, its very difficult to observe them directly (e.g.…”

Inference of Heating Properties From “Hot” Non-Flaring Plasmas in Active Region Cores. Ii. Nanoflare Trains

“…When considering the role of nanoflares in the production of hot plasma in AR cores, it is important to take NEI into account (Bradshaw & Cargill 2006;Reale & Orlando 2008;Barnes et al 2016). In a steady heating scenario, the ionization state is an adequate measure of the electron plasma temperature.…”