Constraining the hard X-ray properties of the quiet Sun with new RHESSI observations

Abstract

We present new RHESSI upper limits in the 3-200 keV energy range for solar hard X-ray emission in the absence of flares and active regions, i.e. the quiet Sun, using data obtained between July 2005 and April 2009. These new limits, substantially deeper than any previous ones, constrain several physical processes that could produce hard X-ray emission. These include cosmic-ray effects and the generation of axions within the solar core. The data also limit the properties of "nanoflares", a leading candidate to explain coronal heating. We find it unlikely for nanoflares involving nonthermal effects to heat the corona because such events would require a steep electron spectrum E^{-δ} with index δ> 5 extending to very low energies (<1 keV), into the thermal energy range. We also use the limits to constrain the parameter space of an isothermal model and coronal thin-target emission models (powerlaw and kappa distributions)

7 pages, 8 Figures, Accepted for publication in ApJ

References in corpus (8)

• An improved limit on the axion-photon coupling from the CAST experiment
• Highly Efficient Modeling of Dynamic Coronal Loops
• RHESSI Microflare Statistics II. X-ray Imaging, Spectroscopy & Energy Distributions
• Kappa distribution and hard X-ray emission of solar flares
• RHESSI Observations of the Solar Flare Iron-line Feature at 6.7 keV
• First limits on the 3-200 keV X-ray spectrum of the quiet Sun using RHESSI
• Quiet Sun X-rays as Signature for New Particles
• A new method of observing weak extended x-ray sources with RHESSI

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