Hard X-Ray Constraints on Small-scale Coronal Heating Events

Author(s): Marsh, AJ; Smith, DM; Glesener, L; Klimchuk, JA; Bradshaw, SJ; Vievering, J; Hannah, IG; Christe, S; Ishikawa, SN; Krucker, S | Abstract: © 2018. The American Astronomical Society. All rights reserved.. Much evidence suggests that the solar corona is heated impulsively, meaning that nanoflares may be ubiquitous in quiet and active regions (ARs). Hard X-ray (HXR) observations with unprecedented sensitivity g3 keV are now enabled by focusing instruments. We analyzed data from the Focusing Optics X-ray Solar Imager (FOXSI) rocket and the Nuclear Spectroscopic Telescope Array (NuSTAR) spacecraft to constrain properties of AR nanoflares simulated by the EBTEL field-line-averaged hydrodynamics code. We generated model X-ray spectra by computing differential emission measures for homogeneous nanoflare sequences with heating amplitudes H 0, durations τ, delay times between events t N, and filling factors f. The single quiescent AR observed by FOXSI-2 on 2014 December 11 is well fit by nanoflare sequences with heating amplitudes 0.02 erg cm-3 s-1 99% confidence for all regions observed by either instrument.