First limits on the 3-200 keV X-ray spectrum of the quiet Sun using RHESSI

Abstract

We present the first results using the Reuven Ramaty High-Energy Solar Spectroscopic Imager, RHESSI, to observe solar X-ray emission not associated with active regions, sunspots or flares (the quiet Sun). Using a newly developed chopping technique (fan-beam modulation) during seven periods of offpointing between June 2005 to October 2006, we obtained upper limits over 3-200 keV for the quietest times when the GOES12 1-8A flux fell below $10^{-8}$ Wm${}^{-2}$. These values are smaller than previous limits in the 17-120 keV range and extend them to both lower and higher energies. The limit in 3-6 keV is consistent with a coronal temperature $\le 6$ MK. For quiet Sun periods when the GOES12 1-8A background flux was between $10^{-8}$ Wm${}^{-2}$ and $10^{-7}$ Wm${}^{-2}$, the RHESSI 3-6 keV flux correlates to this as a power-law, with an index of $1.08\pm 0.13$. The power-law correlation for microflares has a steeper index of $1.29\pm 0.06$. We also discuss the possibility of observing quiet Sun X-rays due to solar axions and use the RHESSI quiet Sun limits to estimate the axion-to-photon coupling constant for two different axion emission scenarios.

arXiv comment4 pages, 3 figures, Accepted by ApJ letters

References in corpus (5)

• First results from the CERN Axion Solar Telescope (CAST)
• Detecting solar axions using Earth's magnetic field
• Pseudoscalar Conversion and X-rays from the Sun
• Quiet Sun X-rays as Signature for New Particles
• A new method of observing weak extended x-ray sources with RHESSI

Cited by in corpus (13)

• RHESSI Microflare Statistics II. X-ray Imaging, Spectroscopy & Energy Distributions
• Microflares and the Statistics of X-ray Flares
• The first X-ray imaging spectroscopy of quiescent solar active regions with NuSTAR
• Constraining the hard X-ray properties of the quiet Sun with new RHESSI observations
• Axion Searches with Helioscopes and astrophysical signatures for axion(-like) particles
• Soft X-ray coronal spectra at low activity levels observed by RESIK
• A Physical Background Model for the Fermi Gamma-ray Burst Monitor
• Solar axions in large extra dimensions
• The First Survey of Quiet Sun Features Observed in Hard X-Rays With NuSTAR
• A New Component from the Quiet Sun: Synchrotron Radiation from Galactic Cosmic-Ray Electrons
• NuSTAR as an Axion Helioscope
• Signatures of Type III Solar Radio Bursts from Nanoflares: Modeling
• Quiet Sun impulsive events observed with NuSTAR during solar minimum