Hinode X-Ray Telescope Detection of Hot Emission from Quiescent Active Regions: A Nanoflare Signature?

TL;DR

This paper reports X-ray observations of a quiescent solar active region that reveal a high-temperature component consistent with nanoflare heating, supported by DEM analysis and modeling.

Contribution

It provides the first detection of high-temperature emission in quiescent regions consistent with nanoflare heating, using Hinode XRT data and DEM modeling.

Findings

Detection of high-temperature component at Log T > 7.0

DEM is down by nearly three orders of magnitude at high temperatures

A simple two-component nanoflare model reproduces the DEM results

Abstract

The X-Ray Telescope (XRT) on the Japanese/USA/UK {\it Hinode (Solar-B)} spacecraft has detected emission from a quiescent active region core that is consistent with nanoflare heating. The fluxes from 10 broadband X-ray filters and filter combinations were used to constructed Differential Emission Measure (DEM) curves. In addition to the expected active region peak at Log T = 6.3-6.5, we find a high-temperature component with significant emission measure at Log T $>$ 7.0. This emission measure is weak compared to the main peak -- the DEM is down by almost three orders of magnitude -- which accounts of the fact that it has not been observed with earlier instruments. It is also consistent with spectra of quiescent active regions: no Fe XIX lines are observed in a CHIANTI synthetic spectrum generated using the XRT DEM distribution. The DEM result is successfully reproduced with a simple two-component nanoflare model.