Hard X-Ray constraints on small-scale coronal heating events

Marsh, A. J., Smith, D. M., Glesener, L., Klimchuk, J. A., Bradshaw, S. J., Vievering, J., Hannah, I. G. , Christe, S., Ishikawa, S.-n. and Krucker, S. (2018) Hard X-Ray constraints on small-scale coronal heating events. Astrophysical Journal, 864(1), 5. (doi:10.3847/1538-4357/aad380)

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Abstract

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 >3 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 <H 0 < 13 erg cm−3 s−1 and a wide range of delay times and durations. We exclude delays between events shorter than ~900 s at the 90% confidence level for this region. Three of five regions observed by NuSTAR on 2014 November 1 are well fit by homogeneous nanoflare models, while two regions with higher fluxes are not. Generally, the NuSTAR count spectra are well fit by nanoflare sequences with smaller heating amplitudes, shorter delays, and shorter durations than the allowed FOXSI-2 models. These apparent discrepancies are likely due to differences in spectral coverage between the two instruments and intrinsic differences among the regions. Steady heating (t N = τ) was ruled out with >99% confidence for all regions observed by either instrument.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Hannah, Dr Iain
Authors: Marsh, A. J., Smith, D. M., Glesener, L., Klimchuk, J. A., Bradshaw, S. J., Vievering, J., Hannah, I. G., Christe, S., Ishikawa, S.-n., and Krucker, S.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astrophysical Journal
Publisher:American Astronomical Society
ISSN:1538-4357
ISSN (Online):1538-4357
Copyright Holders:Copyright © 2018 The American Astronomical Society
First Published:First published in Astrophysical Journal 864(1):5
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher
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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
617954The many scales of flaring energy release on the SunIain HannahThe Royal Society (ROYSOC)UF120063S&E P&A - PHYSICS & ASTRONOMY