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Published March 20, 2016 | Published + Submitted
Journal Article Open

The first X-ray imaging spectroscopy of quiescent solar active regions with NuSTAR

Abstract

We present the first observations of quiescent active regions (ARs) using NuSTAR, a focusing hard X-ray telescope capable of studying faint solar emission from high temperature and non-thermal sources. We analyze the first directly imaged and spectrally resolved X-rays above 2~keV from non-flaring ARs, observed near the west limb on 2014 November 1. The NuSTAR X-ray images match bright features seen in extreme ultraviolet and soft X-rays. The NuSTAR imaging spectroscopy is consistent with isothermal emission of temperatures 3.1 − 4.4~MK and emission measures 1 – 8 × 10^(46)~cm^(−3). We do not observe emission above 5~MK but our short effective exposure times restrict the spectral dynamic range. With few counts above 6~keV, we can place constraints on the presence of an additional hotter component between 5 and 12~MK of ∼ 10^(46)cm^(−3) and ∼10^(43) cm^(−3), respectively, at least an order of magnitude stricter than previous limits. With longer duration observations and a weakening solar cycle (resulting in an increased livetime), future NuSTAR observations will have sensitivity to a wider range of temperatures as well as possible non-thermal emission.

Additional Information

© 2016 The American Astronomical Society. Received 2016 February 8; accepted 2016 March 2; published 2016 March 16. 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, 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). This work is supported by: NASA grants NNX12AJ36G, NNX14AG07G, IGH (Royal Society University Research Fellowship), AM (NASA Earth Space Science Fellowship, NNX13AM41H), SK (Swiss National Science Foundation, 200021-140308), AC (NASA NNX15AK26G, NNX14AN84G). Thanks to Kim Tolbert for OSPEX help.

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Published - apjl_820_1_L14.pdf

Submitted - 1603.01069v1.pdf

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August 22, 2023
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