First Limits on the 3-200 Kev X-ray Spectrum of the Quiet Sun Using Rhessi
نویسنده
چکیده
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 1-8 Å flux fell below 10 Wm. 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 ≤ 6 MK. For quiet Sun periods when the GOES12 1-8 Å background flux was between 10 Wm and 10 Wm, the RHESSI 3-6 keV flux correlates to this as a power-law, with an index of 1.08 ± 0.13. The power-law correlation for microflares has a steeper index of 1.29 ± 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. Subject headings: Sun: X-rays, gamma rays – Sun: activity – Sun: corona – elementary particles
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