NuSTAR’s First Solar Observations: Search for Transient Brightenings / Nanoflares

Monday, 15 December 2014
Andrew Marsh1, Iain G Hannah2, Lindsay Glesener3, David Miles Smith1, Brian Grefenstette4, Sam Krucker3,5, Hugh S Hudson3, Gordon J Hurford3, Stephen White6, Amir Caspi7, Steven Christe8, Albert Shih8, Richard A Mewaldt4, Michael Pivovaroff9 and Julia Vogel9, (1)Univ of California Santa Cruz, Santa Cruz, CA, United States, (2)University of Glasgow, Glasgow, G12, United Kingdom, (3)Space Sciences Laboratory, Berkeley, CA, United States, (4)California Institute of Technology, Pasadena, CA, United States, (5)University of Applied Sciences and Arts Northwestern Switzerland, Windisch, Switzerland, (6)Air Force Research Laboratory, Albuquerque, NM, United States, (7)Laboratory for Atmospheric and Space Physics, Boulder, CO, United States, (8)NASA GSFC, Greenbelt, MD, United States, (9)Lawrence Livermore National Laboratory, Livermore, CA, United States
We present a timing analysis of the Sun with the NuSTAR hard X-ray (HXR) telescope, searching for transient brightenings / nanoflares in the quiet Sun and active regions. A substantial amount of flare energy goes into accelerating electrons. HXR observations are a crucial tool for understanding this non-thermal emission and the energy release in flares. RHESSI is able to study this emission over many orders of magnitude (active region flares from X-class to A-class microflares), but it cannot detect the emission from smaller events. Such “nanoflares” have been postulated as a possible source of coronal heating and their existence and relationship to larger flares is still uncertain. In order to detect these events in HXRs, instruments more sensitive than RHESSI are required. Launched in 2012, the astrophysics mission NuSTAR uses focusing optics to directly image X-rays between ~2-80 keV. Although not optimized for solar observations, NuSTAR’s highly sensitive imaging spectroscopy will be used to search for the faintest X-ray emission from the Sun. These solar observations will begin in September 2014; here we present the first results of our search for transient brightenings that could relate to nanoflares.