First NuSTAR Limits on Quiet Sun Hard X-Ray Transient Events

Research output: Contribution to journalJournal article – Annual report year: 2017Researchpeer-review

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DOI

  • Author: Marsh, Andrew J.

    University of California at Santa Cruz

  • Author: Smith, David M.

    University of California at Santa Cruz, United States

  • Author: Glesener, Lindsay

    University of Minnesota, United States

  • Author: Hannah, Iain G.

    University of Glasgow, United Kingdom

  • Author: Grefenstette, Brian W.

    California Institute of Technology, United States

  • Author: Caspi, Amir

    Southwest Research Institute, United States

  • Author: Krucker, Säm

    University of California at Berkeley, United States

  • Author: Hudson, Hugh S.

    University of Glasgow, United Kingdom

  • Author: Madsen, Kristin K.

    California Institute of Technology, United States

  • Author: White, Stephen M.

    Air Force Research Laboratory, United States

  • Author: Kuhar, Matej

    University of Applied Sciences and Arts Northwestern Switzerland, Switzerland

  • Author: Wright, Jonathan Paul

    University of Glasgow, United Kingdom

  • Author: Boggs, Steven E.

    University of California at Berkeley, United States

  • Author: Christensen, Finn Erland

    Astrophysics and Atmospheric Physics, National Space Institute, Technical University of Denmark, Elektrovej, 2800, Kgs. Lyngby, Denmark

  • Author: Craig, William

    University of California at Berkeley, United States

  • Author: Hailey, Charles J.

    Columbia University, United States

  • Author: Harrison, Fiona A.

    California Institute of Technology, United States

  • Author: Stern, Daniel

    California Institute of Technology, United States

  • Author: Zhang, William

    NASA Goddard Space Flight Center, United States

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We present the first results of a search for transient hard X-ray (HXR) emission in the quiet solar corona with the Nuclear Spectroscopic Telescope Array (NuSTAR) satellite. While NuSTAR was designed as an astrophysics mission, it can observe the Sun above 2 keV with unprecedented sensitivity due to its pioneering use of focusing optics. NuSTAR first observed quiet-Sun regions on 2014 November 1, although out-of-view active regions contributed a notable amount of background in the form of single-bounce (unfocused) X-rays. We conducted a search for quiet-Sun transient brightenings on timescales of 100 s and set upper limits on emission in two energy bands. We set 2.5–4 keV limits on brightenings with timescales of 100 s, expressed as the temperature T and emission measure EM of a thermal plasma. We also set 10–20 keV limits on brightenings with timescales of 30, 60, and 100 s, expressed as model-independent photon fluxes. The limits in both bands are well below previous HXR microflare detections, though not low enough to detect events of equivalent T and EM as quiet-Sun brightenings seen in soft X-ray observations. We expect future observations during solar minimum to increase the NuSTAR sensitivity by over two orders of magnitude due to higher instrument livetime and reduced solar background.
Original languageEnglish
Article number131
JournalAstrophysical Journal Supplement Series
Volume849
Issue number2
Number of pages8
ISSN0067-0049
DOIs
Publication statusPublished - 2017
CitationsWeb of Science® Times Cited: No match on DOI

    Research areas

  • Sun: flares - sun: X-rays, Gamma rays

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ID: 139974679