First NuSTAR limits on quiet sun hard X-ray transient events

Marsh, A. J. et al. (2017) First NuSTAR limits on quiet sun hard X-ray transient events. Astrophysical Journal, 849(2), 131. (doi:10.3847/1538-4357/aa9122)

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Abstract

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:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Hudson, Dr Hugh and Wright, Mr Paul and Hannah, Dr Iain
Authors: Marsh, A. J., Smith, D. M., Glesener, L., Hannah, I. G., Grefenstette, B. W., Caspi, A., Krucker, S., Hudson, H. S., Madsen, K. K., White, S. M., Kuhar, M., Wright, P. J., Boggs, S. E., Christensen, F. E., Craig, W. W., Hailey, C. J., Harrison, F. A., Stern, D., and Zhang, W. W.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astrophysical Journal
Publisher:American Astronomical Society
ISSN:1538-4357
ISSN (Online):1538-4357
Published Online:08 November 2017
Copyright Holders:Copyright © 2017 The American Astronomical Society
First Published:First published in Astrophysical Journal 849(2):131
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher.

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
646461EPSRC-Royal Society fellowship engagement (2013): Heating of the solar atmosphere by small flaresIain HannahEngineering and Physical Sciences Research Council (EPSRC)EP/M00371X/1S&E P&A - PHYSICS & ASTRONOMY
617954The many scales of flaring energy release on the SunIain HannahThe Royal Society (ROYSOC)UF120063S&E P&A - PHYSICS & ASTRONOMY