The nonequilibrium ionization of solar flare coronal plasma and the emergent X-ray spectrum

Abstract

view Abstract Citations (38) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The nonequilibrium ionization of solar flare coronal plasma and the emergent X-ray spectrum. Shapiro, P. R. ; Moore, R. T. Abstract Consequences of a lack of equilibrium between the ionization and recombination of ions in the coronal plasma responsible for the thermal X-ray emission spectrum of solar flares are considered. A model of an impulsively heated nonequilibrium flare plasma is investigated in which a preflare coronal loop is 'instantaneously' heated, with rapid thermalization of the loop electrons occurring at a temperature of the order of 100 million K. It is shown that since the plasma is out of ionization equilibrium during the first few seconds before the onset of some energy-releasing instability, the emergent X-ray spectrum is a superposition of the thermal bremsstrahlung spectrum of hot electrons and the X-ray line and enhanced two-photon continuous spectra of the nonequilibrium ionization structure. Soft X-ray emission from this plasma is therefore burstlike, jumping to a significantly higher level when the electron temperature jumps and decaying dramatically as the gas becomes more ionized. The plasma model is used in a detailed calculation of the ionization structure of and the X-ray emission from the coronal flare plasma during the impulsive phase of solar flares. Publication: The Astrophysical Journal Pub Date: October 1977 DOI: 10.1086/155609 Bibcode: 1977ApJ...217..621S Keywords: Nonequilibrium Ionization; Plasma Temperature; Solar Corona; Solar Flares; Solar X-Rays; Ion Recombination; Radiant Flux Density; Temperature Effects; X Ray Spectra; Solar Physics full text sources ADS |