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

Marsh, Andrew J. and Smith, David M. and Glesener, Lindsay and Hannah, Iain G. and Grefenstette, Brian W. and Caspi, Amir and Krucker, Säm and Hudson, Hugh S. and Madsen, Kristin K. and White, Stephen M. and Kuhar, Matej 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) First NuSTAR Limits on Quiet Sun Hard X-Ray Transient Events. Astrophysical Journal, 849 (2). Art. No. 131. ISSN 1538-4357. doi:10.3847/1538-4357/aa9122.

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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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Marsh, Andrew J.0000-0003-1086-6900
Smith, David M.0000-0002-0542-5759
Glesener, Lindsay0000-0001-7092-2703
Hannah, Iain G.0000-0003-1193-8603
Grefenstette, Brian W.0000-0002-1984-2932
Caspi, Amir0000-0001-8702-8273
Hudson, Hugh S.0000-0001-5685-1283
Madsen, Kristin K.0000-0003-1252-4891
White, Stephen M.0000-0002-8574-8629
Kuhar, Matej0000-0002-7210-180X
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 2017 May 13; revised 2017 October 2; accepted 2017 October 2; published 2017 November 8. 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 has 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). Some of the figures within this paper were produced using IDL color-blind-friendly color tables (Wright 2017). The authors would like to thank Albert Shih for helpful comments and suggestions. A.M. was supported by NASA Earth and Space Science Fellowship award NNX13AM41H. I.G.H. acknowledges support from a Royal Society University Research Fellowship. S.K. acknowledges support from the Swiss National Science Foundation (200021-140308). A.C. was supported by NASA grants NNX15AK26G and NNX14AH54G. L.G. was supported by an NSF Faculty Development Grant to UMN (AGS-1429512). P.J.W. was supported by an EPSRC/Royal Society Fellowship Engagement Award (EP/M00371X/1). This work was supported by NASA grants NNX12AJ36G and NNX14AG07G. Facility: NuSTAR - The NuSTAR (Nuclear Spectroscopic Telescope Array) mission.
Group:NuSTAR, Space Radiation Laboratory, Astronomy Department
Funding AgencyGrant Number
NASA Earth and Space Science FellowshipNNX13AM41H
Swiss National Science Foundation (SNSF)200021-140308
Engineering and Physical Sciences Research Council (EPSRC)EP/M00371X/1
Subject Keywords:Sun: flares – Sun: X-rays, gamma rays
Issue or Number:2
Record Number:CaltechAUTHORS:20171108-103806025
Persistent URL:
Official Citation:Andrew J. Marsh et al 2017 ApJ 849 131
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:83065
Deposited By: Tony Diaz
Deposited On:08 Nov 2017 18:45
Last Modified:15 Nov 2021 19:55

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