Evidence of significant energy input in the late phase of a solar flare from NuSTAR x-ray observations

Kuhar, M. et al. (2017) Evidence of significant energy input in the late phase of a solar flare from NuSTAR x-ray observations. Astrophysical Journal, 835(1), 6. (doi:10.3847/1538-4357/835/1/6)

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We present observations of the occulted active region AR 12222 during the third Nuclear Spectroscopic Telescope ARray (NuSTAR) solar campaign on 2014 December 11, with concurrent Solar Dynamics Observatory (SDO)/AIA and FOXSI-2 sounding rocket observations. The active region produced a medium-size solar flare 1 day before the observations, at ∼18 UT on 2014 December 10, with the post-flare loops still visible at the time of NuSTAR observations. The time evolution of the source emission in the SDO/AIA 335 Å channel reveals the characteristics of an extreme-ultraviolet late-phase event, caused by the continuous formation of new post-flare loops that arch higher and higher in the solar corona. The spectral fitting of NuSTAR observations yields an isothermal source, with temperature 3.8\ndash4.6 MK, emission measure (0.3\ndash1.8) × 10⁴⁶ cm‑3, and density estimated at (2.5\ndash6.0) × 10⁸ cm‑3. The observed AIA fluxes are consistent with the derived NuSTAR temperature range, favoring temperature values in the range of 4.0\ndash4.3 MK. By examining the post-flare loops\rsquo cooling times and energy content, we estimate that at least 12 sets of post-flare loops were formed and subsequently cooled between the onset of the flare and NuSTAR observations, with their total thermal energy content an order of magnitude larger than the energy content at flare peak time. This indicates that the standard approach of using only the flare peak time to derive the total thermal energy content of a flare can lead to a large underestimation of its value.

Item Type:Articles
Keywords:Sun: flares, sun: particle emission, sun: x-rays, gamma rays.
Glasgow Author(s) Enlighten ID:Hudson, Dr Hugh and Wright, Mr Paul and Hannah, Dr Iain
Authors: Kuhar, M., Krucker, S., Hannah, I. G., Glesener, L., Saint-Hilaire, P., Grefenstette, B., Hudson, H. S., White, S. M., Smith, D. M., Marsh, A. J., Wright, P. J., Boggs, S. E., Christensen, F. E., Craig, W. W., Hailey, C. J., Harrison, F. A., Stern, D., and Zhang, W. W.
Subjects:Q Science > QB Astronomy
Q Science > QC Physics
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astrophysical Journal
Publisher:American Astronomical Society
ISSN (Online):1538-4357
Copyright Holders:Copyright © 2017 The American Astronomical Society
First Published:First published in Astrophysical Journal 835(1): 6
Publisher Policy:Reproduced in accordance with the publisher copyright policy

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
617954The many scales of flaring energy release on the SunIain HannahRoyal SocietyUF120063S&E P&A - PHYSICS & ASTRONOMY
646461EPSRC-Royal Society fellowship engagement (2013): Heating of the solar atmosphere by small flaresIain HannahEngineering & Physical Sciences Research Council (EPSRC)EP/M00371X/1S&E P&A - PHYSICS & ASTRONOMY