Elena Dzifčáková

SLIPPING MAGNETIC RECONNECTION, CHROMOSPHERIC EVAPORATION, IMPLOSION, AND PRECURSORS IN THE 2014 SEPTEMBER 10 X1.6-CLASS SOLAR FLARE

We investigate the occurrence of slipping magnetic reconnection, chromospheric evaporation, and coronal loop dynamics in the 2014 September 10 X-class flare. The slipping reconnection is found to be present throughout the flare from its early phase. Flare loops are seen to slip in opposite directions towards both ends of the ribbons. Velocities of 20--40 km,s

H TO Zn IONIZATION EQUILIBRIUM FOR THE NON-MAXWELLIAN ELECTRON κ-DISTRIBUTIONS: UPDATED CALCULATIONS

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Nonthermal and thermal diagnostics of a solar flare observed with RESIK and RHESSI

are found within time windows where the slipping is well resolved. The warm coronal loops exhibit expanding and contracting motions that are interpreted as displacements due to the growing flux rope that subsequently erupts. This flux rope existed and erupted before the onset of apparent coronal implosion. This indicates that the energy release proceeds by slipping reconnection and not via coronal implosion. The slipping reconnection leads to changes in the geometry of the observed structures at the textit{IRIS} slit position, from flare loop top to the footpoints in the ribbons. This results in variations of the observed velocities of chromospheric evaporation in the early flare phase. Finally, it is found that the precursor signatures including localized EUV brightenings as well as non-thermal X-ray emission are signatures of the flare itself, progressing from the early phase towards the impulsive phase, with the tether-cutting being provided by the slipping reconnection. The dynamics of both the flare and outlying coronal loops is found to be consistent with the predictions of the standard solar flare model in 3D.

The Ionization Equilibrium in the Solar Corona for the Electron Power Distribution

New data for the calculation of ionization and recombination rates have been published in the past few years, most of which are included in the CHIANTI database. We used these data to calculate collisional ionization and recombination rates for the non-Maxwellian ?-distributions with an enhanced number of particles in the high-energy tail, which have been detected in the solar transition region and the solar wind. Ionization equilibria for elements H to Zn are derived. The ?-distributions significantly influence both the ionization and recombination rates and widen the ion abundance peaks. In comparison with the Maxwellian distribution, the ion abundance peaks can also be shifted to lower or higher temperatures. The updated ionization equilibrium calculations result in large changes for several ions, notably Fe VIII-Fe XIV. The results are supplied in electronic form compatible with the CHIANTI database.

EUV filter responses to plasma emission for the nonthermal κ-distributions

Aims. We aim to prove and diagnose the occurrence of nonthermal electron distributions in solar flare plasma using X-ray spectral observations. Methods. An M4.9 flare on 2003 January 7/8 was observed with the RESIK instrument in the 3−6 A wavelength range (2− 4k eV) and with RHESSI at energies above 6 keV. The temporal behavior of RESIK flare spectra has been analyzed for two different types of velocity distributions – a thermal (Maxwellian) distribution and a nonthermal plasma distribution of free electrons. The Si xiv, Si xiii ,a nd Sixiid satellite lines observed with RESIK in the 5−6 A range were used to determine the degree of deviation from Maxwellian, and the equivalent non-Maxwellian pseudo-temperature, τ. The diagnostics presented are sensitive to the shape of the distribution in the energy range where the maximum of the electron distribution occurs (where the bulk of electrons reside) and does not include the influence of the shape of the high-energy tail of the distribution. Under the assumption of a Maxwellian distribution of electron velocities, the plasma temperature was determined from an emission measure (EM) loci analysis and a differential emission measure (DEM) analysis of RESIK spectra. The high-energy end of the flare radiative emission was investigated through RHESSI spectral analysis. Results. The nonthermal analysis of RESIK spectra has shown that the largest deviations of the plasma electron distribution from Maxwellian appeared during the impulsive phase of the flare. The decay phase spectra had an almost isothermal character. The pseudotemperature, τ, reached its maximum around the peak time of the soft and hard X-ray fluxes. The temporal behavior of the temperatures derived from the thermal analysis was similar to the behavior of the nonthermal pseudo-temperature. The values of the pseudotemperature were consistent with the temperatures obtained in both thermal analyses, but lower than the temperatures derived from the slope of the RHESSI continua. In comparison with the synthetic isothermal or multithermal spectra, the nonthermal synthetic spectra fitted the observed Si xiid satellite lines much more closely (the error is less than 10%). The fluxes in the Si XIId satellite lines in isothermal or multithermal spectra have been underestimated by a factor of three or more in comparison to the observed fluxes. The value of this factor varies with time and it is different for the different satellite lines. Conclusions. Evidence was found for considerable deviations of the distribution of free electrons from Maxwellian in the plasma during a solar flare. These occurred mainly during the flare impulsive phase and can be diagnosed using existing X-ray spectral observations.

The Updated fe Ionization Equilibrium for the Electron K-Distributions

The influence of an electron non-Maxwellian distribution (power distribution) on the ionization equilibrium of Fe in the solar corona is demonstrated. The results can be used for specific applications in the solar corona, especially in the description of the ionization state of plasma during the impulsive phase of solar flares, where deviations from the Maxwellian distribution may be significant.

Electron Excitation Rates in the Solar Corona for non-Maxwellian Electron Distributions

The responses to plasma emission of the TRACE EUV filters are computed by integrating their spectral responses over the synthetic spectra obtained from the CHIANTI database. The filter responses to emission are functions of temperature, electron density, and the assumed electron distribution function. It is shown here that, for the nonthermal κ-distributions, the resulting responses to emission are more broadly dependent on T , and their maxima are flatter than for the Maxwellian electron distribution. The positions of the maxima can also be shifted. Filter reponses to T are density-dependent as well. The influence of the nonthermal κ-distributions on the diagnostics of T from the observations in all three EUV filters is discussed.

THE Fe XXV EXCITATION EQUILIBRIUM IN THE SOLAR CORONA FOR THE ELECTRON POWER DISTRIBUTIONS USING A PSEUDO-TEMPERATURE

In the past few years new calculations of the ionization and recombination rates have been published. The new Fe ionization equilibrium for these new rates is available for a Maxwellian distribution. Therefore the updated Fe ionization equilibrium for the non-thermal κ-distribution with an enhanced number of particles in the high-energy tail is presented. Results for the various deviations from a Maxwellian distribution are given in tabular form and these are compared with previous ones. A method for the determination of an energy distribution different from the Maxwellian one is suggested.

Nonequilibrium Processes in the Solar Corona, Transition Region, Flares, and Solar Wind (Invited Review)

The influence of electron non-Maxwellian distributions (power and κ-distribution) on the electron excitation rate in the solar corona is demonstrated. It is shown that the deviations in electron excitation rate are sufficient to affect intensities of spectral lines. As an example the diagnostics of a power-law distribution are demonstrated for a simplified calculation of the resonance lines of Feu2009xxiv, Feu2009xxv and Feu2009xxvi. The results can be used in diagnosing solar flare plasmas, where the deviations of the electron distribution from a Maxwellian distribution can be large.

Carbon and Oxygen Coronal Line Intensities for the Electron κ-DistributionI

The excitation equilibrium of Feu2009xxv in the solar corona for electron power distributions is presented. A parametric form of the distribution function is used to demonstrate the changes in the excitation equilibrium due to the shape of the distribution. A pseudo-temperature is used for better understanding of the changes in the excitation equilibrium. The Feu2009xxv line intensities depend on the shape of the electron distribution and unusual Fe line ratios can be observed for non-thermal distribution. The results can be used in specific applications in the solar corona, especially in diagnostics of the impulsive phase of solar flares, where the deviations from the Maxwellian distribution can be large.