Powerful nonstationary processes on the sun: Spatio-temporal structure and efficient particle acceleration |
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Authors: | M A Livshits |
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Institution: | 1.Institute of Terrestrial Magnetism, Ionosphere, and Radiowave Propagation,Russian Academy of Sciences,Troitsk, Moscow oblast,Russia |
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Abstract: | Data on high-energy processes on the Sun are summarized. We refine the classification of flares and substantiate the view
that a coronal mass ejection and a flare proper are manifestations of the same common process, at least for the most powerful
events. Next, we analyze data on the acceleration of electrons (RHESSI, Mars Odyssey) and protons. The existence of two peaks
of hard X-ray emission spaced 10–20 min apart and the evolution of its spectra are shown to be indicative of two acceleration
episodes. We have analyzed the spectra of 172 proton increases identified with the ratio of the proton fluxes at energies
above 10 and 100 MeV near the Earth. These spectra turn out to be virtually the same for most of the large flares under favorable
conditions for the escape of particles from the corona and their propagation in the interplanetary space. This is an argument
for the invariance of the main features of efficient particle acceleration in powerful events. This process takes place at
the explosive phase of a flare and its source is located low, immediately above the chromosphere, in the region adjacent to
sunspots. There is a reason to believe that, in this case, a rapid simultaneous acceleration of electrons and protons takes
place with the capture of some fraction of the particles into magnetic traps. However, there exist a few events in which an
additional number of protons with energies as high as 10–30 MeV escape from the corona at the post-eruptive phase of flare
development. Analysis of these cases with softer particle spectra more likely suggests an additional particle acceleration
at coronal heights (about 30 000 km) than the facilitation of particle escape from magnetic traps. We estimate the contribution
from the proton flux at an energy above 10 MeV arising at the post-eruptive phase of a flare to the total particle flux at
the maximum of a proton increase and discuss possible particle acceleration mechanisms at significant coronal heights. |
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