Shock formation time and the viability of prompt MeV proton shock acceleration in solar flares

Details Shock formation time and the viability of prompt MeV proton shock acceleration in solar flares Shock formation time and the viability of prompt MeV proton shock acceleration in solar flares

Jan 1985

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985jgr....90..205s&link_type=abstract

Journal of Geophysical Research (ISSN 0148-0227), vol. 90, Jan. 1, 1985, p. 205-209.

Physics

13

Gamma Rays, Shock Waves, Solar Electrons, Solar Flares, Solar Protons, Solar X-Rays, Flux Density, Magnetohydrodynamic Waves, Plasma Frequencies

Scientific paper

A critical analysis is made of a proposed mechanism to explain the less than or approximately equal to 2- to 100-s delays observed in some flares between gamma rays due to several MeV protons and hard X-rays due to approximately 100-keV electrons. The proposed mechanism is first-order Fermi acceleration of protons bouncing between two shocks formed by the electrons causing the hard X-rays. For the maximum possible flux for stable beam propagation the shock formation time is found to be greater than or approximately equal to 2 s and the shock velocity less than or approximately equal to 1800 km/s. The mechanism as proposed produces protons which gain only approximately 3 MeV before they are transmitted through the shocks. The mechanism will work with additional pitch angle scattering, which also raises the possibility of multiple encounters with a single shock, a case not analyzed. For this reason the final energy gains of the proposed mechanism may be altered. The times during which this type of shock acceleration could be important and thus the range of observed delays which could be explained are given for a range of loop lengths and injected electron spectra. Alternate possibilities such as stochastic acceleration by hydromagnetic turbulence must be invoked to explain the shortest delays associated with this prompt proton acceleration.

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