2017/11/08 by Andrew Marsh, Andrew J. Marsh, David M. Smith +21 · 1 citation
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Cosmic Phenomena #Optics #Photon #Physics #QUIET #Solar and Space Plasma Dynamics #Telescope #Transient (computer programming) #astro-ph.HE #astro-ph.SR #physics.plasm-ph #physics.space-ph
paper · pdf · doi:10.3847/1538-4357/aa9122
published as The Astrophysical Journal, Vol. 849, Issue 2, 131 (8pp); 2017 November 10 · 11 pages, 7 figures; accepted for publication in The Astrophysical Journal
openalex publication_date 2017/11/08 · arxiv created 2017/11/15 · arxiv updated 2017/11/16 · openalex created_date 2017/11/17 · openalex updated_date 2026/08/06
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.