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Microflare Heating of a Solar Active Region Observed with NuSTAR, Hinode/XRT, and SDO/AIA

Wright, Paul J. and Hannah, Iain G. and Grefenstette, Brian W. and Glesener, Lindsay and Krucker, Säm and Hudson, Hugh S. and Smith, David M. and Marsh, Andrew J. and White, Stephen M. and Kuhar, Matej (2017) Microflare Heating of a Solar Active Region Observed with NuSTAR, Hinode/XRT, and SDO/AIA. Astrophysical Journal, 844 (2). Art. No. 132. ISSN 1538-4357. doi:10.3847/1538-4357/aa7a59.

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NuSTAR is a highly sensitive focusing hard X-ray (HXR) telescope and has observed several small microflares in its initial solar pointings. In this paper, we present the first joint observation of a microflare with NuSTAR and Hinode/XRT on 2015 April 29 at ~11:29 UT. This microflare shows the heating of material to several million Kelvin, observed in soft X-rays with Hinode/XRT, and was faintly visible in the extreme ultraviolet with SDO/AIA. For three of the four NuSTAR observations of this region (pre-flare, decay, and post-flare phases), the spectrum is well fitted by a single thermal model of 3.2–3.5 MK, but the spectrum during the impulsive phase shows additional emission up to 10 MK, emission equivalent to the A0.1 GOES class. We recover the differential emission measure (DEM) using SDO/AIA, Hinode/XRT, and NuSTAR, giving unprecedented coverage in temperature. We find that the pre-flare DEM peaks at ~3 MK and falls off sharply by 5 MK; but during the microflare's impulsive phase, the emission above 3 MK is brighter and extends to 10 MK, giving a heating rate of about 2.5 x 10^(25) erg s^(−1). As the NuSTAR spectrum is purely thermal, we determined upper limits on the possible non-thermal bremsstrahlung emission. We find that for the accelerated electrons to be the source of heating, a power-law spectrum of δ ⩾ 7 with a low-energy cutoff E_(c) ≾ 7 keV is required. In summary, this first NuSTAR microflare strongly resembles much more powerful flares.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Wright, Paul J.0000-0001-9021-611X
Hannah, Iain G.0000-0003-1193-8603
Grefenstette, Brian W.0000-0002-1984-2932
Glesener, Lindsay0000-0001-7092-2703
Hudson, Hugh S.0000-0001-5685-1283
Smith, David M.0000-0002-0542-5759
Marsh, Andrew J.0000-0003-1086-6900
White, Stephen M.0000-0002-8574-8629
Kuhar, Matej0000-0002-7210-180X
Additional Information:© 2017 American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2017 April 12. Accepted 2017 June 16. Published 2017 July 31. This paper 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 the National Aeronautics and Space Administration. 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). Hinode is a Japanese mission developed and launched by ISAS/JAXA, with NAOJ as domestic partner and NASA and STFC (UK) as international partners. It is operated by these agencies in cooperation with ESA and the NSC (Norway). The Atmospheric Imaging Assembly on the Solar Dynamics Observatory is part of NASA's Living with a Star program. CHIANTI is a collaborative project involving George Mason University and the University of Michigan (USA), and the University of Cambridge (UK). This research made extensive use of the IDL Astronomy Library, the SolarSoft IDL distribution (SSW), and NASA's Astrophysics Data System. P.J.W. was supported by an EPSRC/Royal Society Fellowship Engagement Award (EP/M00371X/1) and I.G.H. was supported by a Royal Society University Fellowship. M.K. and S.K. were supported by the Swiss National Science Foundation (project number 200021-140308 and 200020-169046). A.J.M. was supported by NASA Earth and Space Science Fellowship award NNX13AM41H. This work was also supported by NASA grants NNX12AJ36G and NNX14AG07G. The authors thank the International Space Science Institute (ISSI) for support for the team "New Diagnostics of Particle Acceleration in Solar Coronal Nanoflares from Chromospheric Observations and Modeling," where this work benefited from productive discussions. The authors also thank P. J. A. Simões, S. H. Saar, K. K. Reeves, and J. K. Vogel for their valuable comments. Facilities: NuSTAR - The NuSTAR (Nuclear Spectroscopic Telescope Array) mission, Hinode (XRT) - , SDO (AIA) - , GOES.-
Funding AgencyGrant Number
Engineering and Physical Sciences Research Council (EPSRC)EP/M00371X/1
Swiss National Science Foundation (SNSF)200021-140308
Swiss National Science Foundation (SNSF)200020-169046
NASA Earth and Space Science FellowshipNNX13AM41H
Subject Keywords:Sun: activity; Sun: corona; Sun: X-rays, gamma rays
Issue or Number:2
Record Number:CaltechAUTHORS:20170801-090209507
Persistent URL:
Official Citation:Paul J. Wright et al 2017 ApJ 844 132
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:79661
Deposited By: Ruth Sustaita
Deposited On:01 Aug 2017 17:18
Last Modified:15 Nov 2021 17:49

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