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Evidence of Significant Energy Input in the Late Phase of a Solar Flare from NuSTAR X-Ray Observations

Kuhar, Matej and Krucker, Säm and Hannah, Iain G. and Glesener, Lindsay and Saint-Hilaire, Pascal and Grefenstette, Brian W. and Hudson, Hugh S. and White, Stephen M. and Smith, David M. and Marsh, Andrew J. and Wright, Paul J. and Boggs, Steven E. and Christensen, Finn E. and Craig, William W. and Hailey, Charles J. and Harrison, Fiona A. and Stern, Daniel and Zhang, William W. (2017) Evidence of Significant Energy Input in the Late Phase of a Solar Flare from NuSTAR X-Ray Observations. Astrophysical Journal, 835 (1). Art. No. 6. ISSN 0004-637X.

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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 3.8–4.6 MK, emission measure (0.3–1.8) × 10^(46) cm^(−3), and density estimated at (2.5–6.0) × 10^8 cm^(−3). The observed AIA fluxes are consistent with the derived NuSTAR temperature range, favoring temperature values in the range of 4.0–4.3 MK. By examining the post-flare loops' 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:Article
Related URLs:
URLURL TypeDescription
Kuhar, Matej0000-0002-7210-180X
Hannah, Iain G.0000-0003-1193-8603
Glesener, Lindsay0000-0001-7092-2703
Grefenstette, Brian W.0000-0002-1984-2932
Hudson, Hugh S.0000-0001-5685-1283
White, Stephen M.0000-0002-8574-8629
Smith, David M.0000-0002-0542-5759
Marsh, Andrew J.0000-0003-1086-6900
Wright, Paul J.0000-0001-9021-611X
Boggs, Steven E.0000-0001-9567-4224
Christensen, Finn E.0000-0001-5679-1946
Harrison, Fiona A.0000-0003-2992-8024
Stern, Daniel0000-0003-2686-9241
Zhang, William W.0000-0002-1426-9698
Additional Information:© 2017. The American Astronomical Society. Received 2016 October 20. Accepted 2016 November 30. Published 2017 January 16. This work made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by NASA. We thank the NuSTAR Operations, Software and Calibration teams for support with the execution and analysis of these observations. This research made use of the NuSTAR Data Analysis Software (NuSTARDAS), jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA). M.K. and S.K. acknowledge funding from the Swiss National Science Foundation (200021-140308). Funding for this work was also provided under NASA grants NNX12AJ36G and NNX14AG07G. A.J.M.'s participation was supported by NASA Earth and Space Science Fellowship award NNX13AM41H. I.G.H. is supported by a Royal Society University Research Fellowship. P.J.W. is supported by an EPSRC-Royal Society fellowship engagement grant. FOXSI was funded by NASA LCAS grant NNX11AB75G. We would also like to thank the anonymous referee for the helpful comments.
Group:NuSTAR, Space Radiation Laboratory, Astronomy Department
Funding AgencyGrant Number
Swiss National Science Foundation (SNSF)200021-140308
NASA Earth and Space Science FellowshipNNX13AM41H
Engineering and Physical Sciences Research Council (EPSRC)UNSPECIFIED
Subject Keywords:Sun: flares; Sun: particle emission; Sun: X-rays, gamma rays
Issue or Number:1
Record Number:CaltechAUTHORS:20170120-102600412
Persistent URL:
Official Citation:Matej Kuhar et al 2017 ApJ 835 6
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:73571
Deposited By: Ruth Sustaita
Deposited On:22 Jan 2017 17:00
Last Modified:04 Dec 2019 23:51

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