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

Journal Article · Sat Oct 15 04:00:00 EDT 1977 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/155609· OSTI ID:5299125

Shapiro, P R; Moore, R T

The effect of temperature changes in coronal plasma during a solar flare which are more rapid than the characteristic ionization and recombination times of the plasma ions is considered. Such temperature changes imply a lack of equilibrium between the ionization and recombination of coronal ions. It is found that the coronal plasma responsible for the ''gradual'' phase of flare soft X-ray emission does not experience such a lack of equilibrium, unless present estimates of its electron density (> or approx. =10/sup 10/ cm/sup -3/) are overestimates. However, it is argued that for coronal plasma which is impulsively heated at the time of the primary energy-releasing instability of the solar flare, the emergent X-ray spectrum is dramatically affected by nonequilibrium ionization.A model is presented in which a magnetic loop of preflare coronal plasma in ionization equilibrium at a typical quiet coronal temperature (approx.2 x 10/sup 6/ K) and at a density of between 10/sup 10/ amd 10/sup 11/ cm/sup -3/ is heated within a fraction of a second to a much higher temperature (>10/sup 7/ K). This heating results from the thermalization within the loop of accelerated electrons such as those which fill the low-energy (approx.10 keV) end of the power-law distribution of electrons usually believed responsible for flare hard X-ray bursts. A weak, R-type conduction front is subsequently caused to propagate in the loop downward toward the chromosphere. During the first seconds after heating, the loop plasma is out of ionization equilibrium, resulting in the emission of a burst of soft X-rays. We calculate the details of this model, including the time-dependent ionization structure of the plasma and the emergent X-ray line and continuum spectrum from 1 to 250 A.

• Research Organization: Center for Astrophysics, Harvard College Observatory and Smithsonian Astrophysical Observatory
• OSTI ID: 5299125
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 217:2; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640104* -- Astrophysics & Cosmology-- Solar Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COLLISIONS
ELECTRON COLLISIONS
ELECTRON-ELECTRON COLLISIONS
IONIZATION
MAGNETIC FIELDS
PLASMA
SOLAR ACTIVITY
SOLAR CORONA
SOLAR FLARES
SOLAR X-RAY BURSTS
SPECTRA
X-RAY SPECTRA