NuSTAR’s first solar observations: Search for a high energy X-ray component to the “non-flaring” Sun

Iain G Hannah1, Andrew Marsh2, Lindsay Glesener3, David Miles Smith4, Brian Grefenstette5, Sam Krucker6, Hugh S Hudson7, Gordon J Hurford8, Stephen M White9, Amir Caspi10, Steven Christe11, Albert Y Shih11, Richard Mewaldt12, Michael Pivovaroff13, Julia Vogel13 and The NuSTAR Science Team, (1)University of Glasgow, Glasgow, United Kingdom, (2)University of California Santa Cruz, Santa Cruz, CA, United States, (3)University of Minnesota Twin Cities, Minneapolis, United States, (4)University of California Santa Cruz, Department of Physics and Santa Cruz Institute for Particle Physics, Santa Cruz, CA, United States, (5)California Institute of Technology, Pasadena, United States, (6)Space Sciences Laboratory, Berkeley, United States, (7)Space Sciences Laboratory, Berkeley, CA, United States, (8)Univ California, Berkeley, CA, United States, (9)Air Force Research Laboratory, Albuquerque, NM, United States, (10)Southwest Research Institute, Boulder, CO, United States, (11)NASA GSFC, Solar Physics Lab, Greenbelt, United States, (12)California Institute of Technology, Pasadena, CA, United States, (13)Lawrence Livermore National Laboratory, Livermore, CA, United States
Abstract:
We present spectroscopy of the Sun with the NuSTAR hard X-ray (HXR) telescope, searching for high temperature and non-thermal emission in the “non-flaring” Sun. 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 in active and quiet Sun regions with NuSTAR.
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