X-ray Spectra Of Solar Flares Research Articles

High-resolution X-ray spectra of solar flares. VIII - Mass upflow in the large flare of 1980 November 7

view Abstract Citations (29) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High-Resolution X-Ray Spectra of Solar Flares. VIII. Mass Upflow in the Large Flare of 1980 November 7 Karpen, J. T. ; Doschek, G. A. ; Seely, J. F. Abstract The large flare of November 7, 1980 provides a unique opportunity to investigate the upward-moving plasma seen during the early stages of many flares. Soft X-ray spectroscopic data obtained by the Solar Flare X-ray (SOLFLEX) instruments on board the Air Force P78-1 satellite have been used to determine the spatial extent, turbulent velocity, temperature, and emission measure of the blueshifted and stationary plasmas, as well as the upward velocity of the blueshifted component alone. Two geometries are considered in calculating the resultant mass and energy balance. In addition, coincident hard X-ray data was acquired from the HXRBS instrument on board the SMM satellite to determine the relative timing and enertics of the hard and soft X-ray flare plasmas. These results are compared with the predictions of the chromospheric evaporation hypothesis. It is concluded that electron-induced evaporation plays a minor role in this flare, and that another mechanism must account for the observed blueshifted emission. Publication: The Astrophysical Journal Pub Date: July 1986 DOI: 10.1086/164346 Bibcode: 1986ApJ...306..327K Keywords: Atmospheric Circulation; Mass Flow; Solar Atmosphere; Solar Flares; Solar X-Rays; X Ray Spectra; High Resolution; Spaceborne Astronomy; Astrophysics; SUN: ATMOSPHERIC MOTIONS; SUN: FLARES; SUN: X-RAYS; X-RAYS: SPECTRA full text sources ADS | Related Materials (8) Part 1: 1979ApJ...233L.157D Part 2: 1980ApJ...238..365F Part 3: 1980ApJ...239..725D Part 4: 1980ApJ...241.1175F Part 5: 1981ApJ...245..315D Part 6: 1982ApJ...260..885F Part 7: 1985ApJ...292..309K Part 9: 1989ApJ...345.1079D

The effect of anisotropy of accelerated electrons on hard X-ray spectra of solar flares

The calculations of X-ray spectra of solar flares were made analytically taking account of electron multiple scattering and radiation reflection from the photospere. They showed a strong dependence of the radiation spectrum shape on the heliocentric angle of the flares. The analysis of the mean radiation spectra hardness versus the observation angle of the flares detected by SIGN-2M3 instruments in the range of 50–300 keV revealed a systematical softening of the spectra towards the centre of the solar disk. The comparison of the calculated radiation spectra with the observed ones points to the generation of electrons with anisotropic angular distribution in solar flares.

Investigations of turbulent motions and particle acceleration in solar flares

Investigations of X-ray spectra of solar flares show that intense random (turbulent) motions are present in hot flare plasma. Here we argue that the turbulent motions are of great importance for flare development. They can efficiently enhance flare energy release and accelerate particles to high energies.

High-resolution X-ray spectra of solar flares. VII - A long-duration X-ray flare associated with a coronal mass ejection

view Abstract Citations (12) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High-resolution X-ray spectra of solar flares. VII - A long-duration X-ray flare associated with a coronal mass ejection Kreplin, R. W. ; Doschek, G. A. ; Feldman, U. ; Sheeley, N. R., Jr. ; Seely, J. F. Abstract It has been recognized that very long duration X-ray events (lasting several hours) are frequently associated with coronal mass ejection. Thus, Sheeley et al. (1983) found that the probability of the occurrence of a coronal mass ejection (CME) increases monotonically with the X-ray event duration time. It is pointed out that the association of long-duration, or long-decay, X-ray events (LDEs) with CMEs was first recognized from analysis of solar images obtained by the X-ray telescopes on Skylab and the Naval Research Laboratory (NRL) slitless spectroheliograph. Recently high-resolution Bragg crystal X-ray spectrometers have been flown on three spacecraft, including the Department of Defense P78-1 spacecraft, the NASA Solar Maximum Mission (SMM), and the Japanese Hinotori spacecraft. In the present paper, P78-1 X-ray spectra of an LDE which had its origin behind the solar west limb on November 14, 1980 is presented. The obtained data make it possible to estimate temperatures of the hottest portion of the magnetic loops in which the emission arises. Publication: The Astrophysical Journal Pub Date: May 1985 DOI: 10.1086/163161 Bibcode: 1985ApJ...292..309K Keywords: Solar Flares; Solar X-Rays; Stellar Mass Ejection; X Ray Spectra; Calcium; Iron; Solar Corona; Spectral Line Width; Solar Physics full text sources ADS | Related Materials (8) Part 1: 1979ApJ...233L.157D Part 2: 1980ApJ...238..365F Part 3: 1980ApJ...239..725D Part 4: 1980ApJ...241.1175F Part 5: 1981ApJ...245..315D Part 6: 1982ApJ...260..885F Part 8: 1986ApJ...306..327K Part 9: 1989ApJ...345.1079D

Measurement of Wavelengths and Abundances from Solar Flare X-Ray Spectra

The measurement of transition energies in highly charged ions represents an important test of quantum electrodynamics (QED) in strong fields. The OED contributions to the hydrogenic transition energies increase as (αZ)4, where α is the fine structure constant and Z is the atomic number. Transitions in hydrogenic ions of sulfur, chlorine, argon, and iron have previously been measured to a precision of 100 ppm or better. These measurements are in satisfactory agreement with accurate calculations of the energy levels, and this confirms the calculation of the QED contributions to the energy levels of one-electron ions.

Atomic Calculations for the Highly Ionized Iron Ions Produced in Solar Flares

The XUY (90–150 Å) and X-ray (10–25 Å) spectra of solar flares are rich in lines from the highly ionized iron ions. Atomic data have been calculated for Fe XVIII (Bhatia, unpublished), Fe XIX (Loulergue et al., 1984, Bhatia and Mason, 1984), Fe XX (Mason and Bhatia, 1980, 1983), Fe XXI (Mason et al., 1979), Fe XXII (Mason and Storey, 1980), Fe XXIII (Bhatia and Mason, 1981), Fe XXIV (Hayes, 1979). The University College London computer package was used. This consists of an atomic structure code (SUPERSTRUCTURE, Eissner et al., 1974); a ‘distorted wave’ electron scattering program (COLLDW, Eissner and Seaton, 1972); a ‘Bethe’ approximation electron scattering program (Burgess and Shoerey, unpublished); a program for obtaining electron collision strength in pair coupling from R matrices in LS coupling (JAJOM, Saraph, 1972); a proton scattering program (Bely and Faucher, 1970) and a program for obtaining level populations and intensity ratios.

Solar flare X-ray spectra from the P78-1 spacecraft

Results from the high resolution solar X-ray spectrometer experiments on the P78-1 spacecraft are discussed. These results concern physical quantities such as electron temperature and density, turbulence, mass motions, and state of ionization equilibrium, characteristic of the thermal soft X-ray emitting flare plasma, and the time behavior of these quantities during flares. In addition, a brief description of the instruments is given, the plasma diagnostics used in interpreting the spectra are summarized, and the origin of the thermal soft X-ray emitting plasma is discussed in light of the P78-1 results, earlier data, and numerical simulations of magnetic flux tubes heated to solar flare temperatures.

Inner-shell transitions in Fe XIX-XXII in the X-ray spectra of solar flares and Tokamaks

Calculated spectra of the ions Fe XIX-XXII for various densities and temperatures are presented, thereby extending the work begun by Doschek, Feldman, and Cowan (1981). The calculations are based on a code (the Cowan code) that computes both the level structure of an ion and intensity factors for the 1s-2p satellite lines. A comparison is made between the calculated spectra and those observed in solar flares by the P78-1 and SMM instruments. The observed intensities of Fe XX lines, which are the most sensitive to density, are found to agree well with those calculated in the low-density limit. The agreement for lines arising from other ions is also very good. It is also seen that the predicted density variations in Fe XX are confirmed by the higher density Princeton Large Torus plasmas. Thus a possible useful density diagnostic is indicated for tokamak and high-density astrophysical plasmas, perhaps including some solar flares.

High-resolution X-ray spectra of solar flares. VI - Impulsive soft X-ray flares

Doschek et al. (1980) and Feldman et al. (1980) have discussed high-resolution soft X-ray spectra of solar flares. The present investigation is concerned with the characteristics of the impulsive events as observed in soft X rays and the cooling of the flare plasma in terms of energy loss processes. A class of intense, short-lived solar flares which appear to be characterized by very high densities at high temperatures is found. For the 1979 November 6 event, the cooling time is so rapid that the density obtained may be a lower limit. The main cooling mechanism for the flares is found to be radiative. Two of the events are associated with strong gamma-ray emission and both of these events are very unusual in their soft X-ray emission. The 1979 November 9 flare shows extremely broad X-ray emission lines during the rise phase, indicative of nonthermal velocities of the order of 300 km/s.

A possible explanation of non-steady-state appearances in X-ray spectra of solar flares

A model of essentially transient ionization of plasma is suggested to explain some features in observed spectra of solar flares, which cannot be understood if stationary conditions are assumed.

Observational constraints for a theoretical model describing the soft X-ray flare

view Abstract Citations (27) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observational constraints for a theoretical model describing the soft X-ray flare Feldman, U. ; Cheng, C. -C. ; Doschek, G. A. Abstract High-resolution solar flare X-ray spectra have recently been obtained from X-ray spectrometer experiments flown on an Air Force spacecraft (P78-1) launched on 1979 February 24. Interpretation of the spectra has produced new results concerning the physical conditions and time behavior of the thermal soft X-ray emitting plasma at temperatures near 20,000,000 K. It is argued that soft and hard X-ray events are not causally related to each other, but are simply two different manifestations of flare energy release. They probably occur in different plasma volumes. The source of the preflare plasma appears to be in the cooler parts of the solar atmosphere, perhaps transition region loops with initial temperatures of 100,000 K and densities of 10 to the 11th per cu cm. Continuous energy input, rather than sequential activation of loops, is required to explain the observations. Compression coupled with chromospheric ablation may produce the high densities in coronal flare loops. Publication: The Astrophysical Journal Pub Date: April 1982 DOI: 10.1086/159832 Bibcode: 1982ApJ...255..320F Keywords: Chromosphere; Coronal Loops; Solar Flares; Solar X-Rays; Stellar Models; X Ray Spectra; Electron Density (Concentration); Electron Energy; High Resolution; Line Spectra; Solar Atmosphere; Spaceborne Experiments; Spectrum Analysis; Solar Physics full text sources ADS |

High-resolution solar flare X-ray spectra obtained with rotating spectrometers on the HINOTORI satellite

view Abstract Citations (115) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High-resolution solar flare X-ray spectra obtained with rotating spectrometers on the HINOTORI satellite Tanaka, K. ; Watanabe, T. ; Nishi, K. ; Akita, K. Abstract Rotating crystal spectrometer observations of an impulsive flare are reported. The resolved spectrum of Fe XXVI and its time variations are presented and various plasma parameters are derived from the spectra of Fe XXIV, Fe XXV, and Fe XXVI. For an impulsive X2.2 flare that occurred on April 2, 1981, time profiles of various line intensities, line widths, and plasma parameters are derived. Increases of electron temperatures and a decrease of the line width are found to occur with steady increases of the line fluxes and the smooth hard X-ray burst. A large emission measure and high density was found for the Fe XXVI emitting plasma. Publication: The Astrophysical Journal Pub Date: March 1982 DOI: 10.1086/183756 Bibcode: 1982ApJ...254L..59T Keywords: Solar Flares; Solar Spectrometers; Solar X-Rays; X Ray Spectroscopy; High Resolution; Ionization; Iron; Japanese Space Program; Solar Physics full text sources ADS |

High resolution solar flare X-ray spectra - The temporal behavior of electron density, temperature, and emission measure for two class M flares

view Abstract Citations (86) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High resolution solar flare X-ray spectra - The temporal behavior of electron density, temperature, and emission measure for two class M flares Doschek, G. A. ; Feldman, U. ; Landecker, P. B. ; McKenzie, D. L. Abstract High resolution soft X-ray flare spectra recorded by Naval Research Laboratory (NRL) and Aerospace Corporation Bragg crystal spectrometers flown on an orbiting spacecraft (P78-1) are combined and analyzed. The instruments were launched on t979 February 24 by the U.S. Air Force, and the data discussed in this paper cover the wavelength ranges, 1.82-1.97 Å, 3.143.24 Å, and 18.423.0 Å. The NRL experiment (SOLFLEX) covers the two short wavelength ranges (highly ionized Fe and Ca lines) and the Aerospace experiment (SOLEX) covers the t8.4-23.O Å range, which includes the Lyα O VIII line and the resonance, intercombination, and forbidden lines of O VII. We analyze the spectra of two flares which occurred on 1980 April 8 and May 9. Temporal coverage is fairly complete for both flares, including the rise and decay phases. Measurements of electron density Ne with rather high time resolution (about 1 minute) have been obtained throughout most of the lifetimes of the two flares. These measurements were obtained from the O VII lines and pertain to flare plasma at temperatures near 2 × 106 K. Peak density seems to occur slightly before the times of peak X-ray flux in the resonance lines of Fe XXV, Ca XIX, and O VII, and for both flares the peak density is about 1012 cm-3. Electron temperature Te as a function of time is determined from the Fe and Ca spectra. Peak temperature for both flares is about 18 × 106 K. Differential emission measures and volume emission measures are determined from the resonance lines of O VII, Ca XIX, and Fe XXV. The number of electrons NeΔV and the volume ΔV over which the O VII lines are formed are determined from the O VII volume emission measure Ne2ΔV and the density Ne. These quantities are determined as a function of time. The relationship of the low and high temperature regions is discussed. Publication: The Astrophysical Journal Pub Date: October 1981 DOI: 10.1086/159294 Bibcode: 1981ApJ...249..372D Keywords: Line Spectra; Solar Flares; Solar Spectra; Solar X-Rays; Temporal Resolution; X Ray Spectra; Electron Density (Concentration); Electron Energy; Emission Spectra; Forbidden Bands; High Resolution; Plasma Density; Plasma Temperature; Resonance Lines; Solar Temperature; Spaceborne Astronomy; Solar Physics full text sources ADS |

A discussion of theoretical ionization equilibrium calculations based on solar flare X-ray spectra

Several sets of ionization equilibrium calculations exist for use in interpreting X-ray and EUV spectra of astrophysical plasmas. In particular, the calculations of Jordan (1969, 1970), Jacobs et al. (1977, 1978) and Summers (1974) are well known. The temperatures of maximum fractional abundance calculated by Summers for the more highly ionized and heavier elements such as iron are about a factor of two higher than the temperatures calculated by Jordan and Jacobs et al. By the use of recently obtained X-ray spectra of solar flares, it is shown that the temperatures calculated by Summers (1974) for iron are incorrect. The temperatures calculated by Jordan or Jacobs et al. should be used until further improvements become available.

Analysis of series of solar flare X-ray spectra

Thirteen X-ray line spectra (7.8 to 23.0 A) acquired during a solar flare that peaked at 2326 UT were analyzed. The data include fluxes of lines excited throughout the temperature range present in the coronal flare. The coronal flare emission measure began to decrease 500 s or less after the broad band X-ray flux peaked. The differential emission measure was calculated from the data by using collision strengths for a small number of the observed lines.

High resolution X-ray spectra of solar flares. V - Interpretation of inner-shell transitions in Fe XX-Fe XXIII

The paper examines high-resolution solar flare iron line spectra recorded between 1.82 and 1.97 A by a spectrometer flown by the Naval Research Laboratory on an Air Force spacecraft launched on 1979 February 24. The emission line spectrum is due to inner-shell transitions in the ions Fe XX-Fe XXV. Using theoretical spectra and calculations of line intensities obtained by methods discussed by Merts, Cowan, and Magee (1976), electron temperatures as a function of time for two large class X flares are derived. These temperatures are deduced from intensities of lines of Fe XXII, Fe XXIII, and Fe XXIV. The determination of the differential emission measure between about 12-million and 20-million K using these temperatures is considered. The possibility of determining electron densities in flare and tokamak plasmas using the inner-shell spectra of Fe XXI and Fe XX is discussed.

X-ray spectra of solar flares obtained with a high-resolution bent crystal spectrometer

Preliminary results obtained for three solar flares with the bent crystal spectrometer on the SMM are presented. Resonance and satellite lines of Ca XIX and XVIII and Fe XXV and XXIV are observed together with the Fe XXVI Lyman-alpha line. Plasma properties are deduced from line ratios and evidence is presented for changes of line widths coincident with the occurrence of a hard X-ray impulsive burst. Fe K-alpha spectra from a disk center and a limb flare agree with the predictions of a fluorescence excitation model. However, a transient Fe K-alpha burst observed in a third flare may be explained by the collisional ionization of cool iron by energetic electrons.

On Doppler shifts of the Fe XXV ion resonance line in solar flare X-ray spectra

Doppler shifts of the Fe xxv line in three solar flares show prevalently downward motions with velocities up to 200 km s−1.

High-resolution X-ray spectra of solar flares. IV - General spectral properties of M type flares

view Abstract Citations (119) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High-resolution X-ray spectra of solar flares. IV - General spectral properties of M type flares Feldman, U. ; Doschek, G. A. ; Kreplin, R. W. ; Mariska, J. T. Abstract The spectral characteristics in selected narrow regions of the X-ray spectrum of class M solar flares are analyzed. High-resolution spectra in the ranges 1.82-1.97, 2.98-3.07, 3.14-3.24 and 8.26-8.53 A, which contain lines important for the determination of electron temperature and departure from ionization equilibrium, were recorded by spaceborne Bragg crystal spectrometers. Temperatures of up to 20,000,000 K are obtained from line ratios during flare rise phases in M as well as X flares, while in the decay phase the calcium temperature can be as low as 8,000,000 K, which is significantly lower than in X flares. Large nonthermal motions (on the order of 130 km/sec at most) are also observed in M as well as X flares, which are largest during the soft X-ray rise phase. Finally, it is shown that the method proposed by Gabriel and Phillips (1979) for detecting departures of electrons from Maxwellian velocity distributions is not sufficiently sensitive to give reliable results for the present data. Publication: The Astrophysical Journal Pub Date: November 1980 DOI: 10.1086/158434 Bibcode: 1980ApJ...241.1175F Keywords: Solar Flares; Solar Spectra; Solar X-Rays; X Ray Spectra; Electron Energy; High Resolution; Spectral Line Width; Solar Physics full text sources ADS | Related Materials (8) Part 1: 1979ApJ...233L.157D Part 2: 1980ApJ...238..365F Part 3: 1980ApJ...239..725D Part 5: 1981ApJ...245..315D Part 6: 1982ApJ...260..885F Part 7: 1985ApJ...292..309K Part 8: 1986ApJ...306..327K Part 9: 1989ApJ...345.1079D

Solar flare X-ray spectra between 7.8 and 23.0 angstroms

Abstract : We present high resolution x-ray spectra taken during a large solar flare on 10 June 1979. Many lines of highly ionized iron are resolved and identified for the first time in solar spectra. Lines with a wide range of excitation temperatures are found to have a similar time development during the flare's rapid rise phase. We discuss density-sensitive line ratios in Fe XXI and Fe XXII. (Author)