Ions In Solar Flares Research Articles

Emission Line Intensity Ratios of Fe xxvi/ xxv/ xxiv in Solar Flares Observed by Hinotori

High-resolution spectra observed by the Solar X-ray spectrometer on board the Hinotori mission are revisited. Flat crystals slightly offset to the satellite spin axis produce automatic spectral scans for emission lines emerging from highly charged iron ions in solar flares every half-spin time period. All the downlinked data of the mission are converted to FITS format and major flare spectral data are revived as IDL save files in ISAS/DARTS. Based on these data sets, single-temperature fits are performed for the emission line complex of highly charged iron ions in the wavelength range of 1.75–1.95 Å and compared with theoretical predictions. Synthetic spectra with single electron temperatures estimated from j/w line-intensity ratios fit fairly well for Fe xxiv and Fe xxiii lines in the wavelength range of 1.85–1.88 Å, while intensity ratios of Fe xxv lines (x, y, z) and the inner-shell excitation line of Fe xxiv (q) to the Fe xxv resonance line (w) have systematic excesses. Empirical relations for the observed line ratios are derived. Ion fractions of Fe+25/Fe+24 estimated by intensity ratios of Lyα/w in the temperature range of log T e =7.25–7.45 are consistent with values in ionization equilibrium, and the remaining excesses of the Fe xxv line ratios may suggest problems with the atomic parameters or atomic modeling.

Spectroscopic EUV observations of impulsive solar energetic particle event sources

Context. Remote observations of solar flare ion acceleration are rather limited. Theoretical predictions for signatures of ion acceleration in extreme ultraviolet (EUV) line profiles have been made. Previous tests involve observations of flares with no evidence for energetic ions. Aims. We aim to examine a source flare of impulsive (or 3He-rich) solar energetic particle events with EUV line spectroscopy. Methods. We inspected all (more than 90) reported 3He-rich flares of the previous solar cycle 23 and found only 4 (recurrent) jets in the field of view of the Coronal Diagnostic Spectrometer (CDS) on board the Solar and Heliospheric Observatory (SOHO). The jet with the most suitable spatial and temporal coverage was analyzed in detail. Results. Two enhanced (nonthermal) line broadenings are observed in the cooler chromospheric and transition-region lines, and they are localized near the site where the closed magnetic loops reconnect with the open magnetic field lines. The enhanced broadenings are both found at the sites with redshifts in the lines, surrounded by the region with blueshifts. One enhanced line broadening is associated with a small flare without energetic particle signatures, while another occurs just after the particle acceleration signatures of the main flare terminated. Conclusions. The observed excess broadening does not appear to be directly related to the energetic ion production and motions. Further investigations are required that cover the critical impulsive phase of the flare, ideally with high-resolution spectrometers that are specifically pointed to the 3He-rich solar energetic particle source.

Shapes of 20Ne de-excitation line in solar flare

Since almost all de-excitation lines from nuclear states excited by flare-accelerated protons and $\alpha $ -particles are emitted promptly after nuclear collisions, the emission photon’s energy depends on the velocity of the recoiling nucleus. The energies and widths of $\gamma $ -ray lines provide a wealth of information on the directionality and spectra of ions in solar flares. In this paper, we use TALYS code to improve the cross sections of $\gamma $ -ray lines production, and calculate the shapes of the 1.634 MeV line from de-excitation of 20Ne as a function of ion’s energy spectra and the heliocentric angle. Taking this line shape as an example, we try to develop a new method of line shape analysis to study the properties of accelerated ions in solar flares.

Nuclear γ-ray line emission induced by energetic ions in solar flares and by galactic cosmic rays

The γ-ray spectra ol the strongest solar flares often show a broad and complex structure in the 0.1-10 MeV region sitting on a bremsstrahlung continuum. This structure is composed of several outstanding narrow lines and of thousands of unresolved narrow and broad lines forming a quasi-continuum. The major part of this emission is due to prompt deexcitation lines following nuclear interactions of accelerated light and heavy ions with the atomic nuclei composing the solar atmosphere. A similar emission is expected from interactions of galactic cosmic rays with the interstellar gas and dust. Experimental nuclear reaction studies coupled with extensive calculations have been done in the last one and a half decade at Orsay for the modelisation of this γ-ray emission. After a description of the nuclear reaction studies the analysis of one solar flare spectrum and predictions for the emission from the inner Galaxy will be presented.

The Calculation of Solar Gamma-Rays by TALYS

Solar gamma-ray lines, produced from nuclear reactions of accelerated particles interacting with the solar atmospheric medium, are the most direct diagnosis for the acceleration and transportation of energetic electrons and ions in solar flares. Much information about composition, spectrum, and angular distribution of the accelerated ions, as well as the elemental abundances of the ambient solar atmosphere can be derived from solar gamma-ray line spectra. A new gamma-ray calculation program has been developed by using an efficient nuclear code − TALYS. The theory of gamma-ray production in solar flares is treated in detail. The characteristics of gamma-ray spectrum are also presented.

Puzzles and potential for gamma-ray line observations of solar flare ion acceleration

The best tool for understanding ion acceleration in solar flares is gamma-ray line emission from nuclear de-excitation, positron annihilation, and neutron capture. These techniques have not yet come close to reaching their potential due to limited counting statistics in the lines. Instruments with focusing optics and large effective areas promise real breakthroughs in understanding high-energy solar processes. I discuss what can be learned from the various lines and the instrumental requirements for future focusing observations.

Solar Gamma-Ray Line Spectroscopy – Physics of a Flaring Star

We discuss how gamma-ray spectroscopy provides information about the acceleration and transport of electrons and ions in solar flares, and their interaction with the solar atmosphere. Temporal studies illuminate differences in the acceleration and transport of electrons and ions. Nuclear line studies reveal the elemental abundance, density, and temperature of the ambient solar atmosphere; and the spectrum, composition, and directionality of the accelerated ions.

Production of γ-ray lines by energetic ion interactions (determination of solar atmospheric abundances)

Acceleration of energetic ions in solar flares produces narrow and broad nuclear γ-ray de-excitation lines, by nuclear interactions with the ambient solar atmosphere. Observations of several solar flare γ-ray spectra have been made since 1972 by satellite-borne γ-ray spectrometers on OSO 7, HEAO 3, SMM, HINOTORI, GRANAT, YOHKOH and CGRO. The line intensities depend directly on the ambient and accelerated particle abundances. In addition, production of neutrons in several reactions leads to emission of the neutron–proton capture γ-ray line, from the photosphere, at an energy of 2.223 MeV. The rate of decay in intensity of this line depends on the photospheric 3He/H abundance ratio. Current analysis gives a photospheric 3He/H abundance ratio of (2.3±1.2)×10 5. In addition, a study of narrow γ-ray line fluxes from several flares suggests that the ratio of (Mg + Si + Fe) to (C + N + O) abundances changes with time during the flare. Since this ratio measures the abundance ratio of low first ionization potential (FIP) elements to high FIP elements, the γ-ray production site may start in the lower chromosphere and move, as the flare progresses, into the corona where the low/high FIP abundance ratio increases. A study of broad γ-ray line fluxes also permits a determination of the abundance of flare-accelerated heavy ions.

A regularization approach for the analysis of RHESSI X-ray spectra

The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) mission provides high resolution X-ray spectra emitted by collisional bremsstrahlung of electrons with the ions of the plasma. One of the aims of the mission is to infer information about the acceleration and transport mechanisms of electrons and ions in solar flares. Within the framework of an optically thin model and under the assumption of isotropic conditions in the solar plasma, the emitted photon spectrum is related to the electron flux density spectrum by an integral equation of the first kind. This problem is characterized by a notable numerical instability as a consequence of the experimental errors in the measured photon data. We address the solution of this problem by using the Tikhonov regularization algorithm. The method is applied to the case of three photon spectra registered by RHESSI detectors in the first months of the observational activity of the satellite. Furthermore a comparison of the reconstructions provided by the algorithm is performed in the case of the Kramers, Bethe-Heitler and Bethe-Heitler with the Elwert correction models for the bremsstrahlung cross-section.

Charge state behaviour of projectiles under an acceleration mechanism in a hot plasma

We have studied the ionization states of most ions in solar flares when a stochastic acceleration mechanism is present. Calculations using a computer code (ESCAPE) designed to find the charge states of heavy and light ions under stochastic acceleration have shown an energy dependence on the ionization states, stronger for heavy ions. Moreover the charge states depend on source parameters as density or temperature, but if an acceleration mechanism is taken into account in impulsive solar energetic particles events, the same source temperature may not be inferred for all the ions.

Particle charge evolution during acceleration processes in solar flares

It has been customary to assume that the charge state of energetic particles corresponds to the ionization equilibrium of the ambient plasma within the acceleration region. Nonetheless, we ascribe to a different opinion, by suggesting that charge interchange mechanisms may be activated during the ensuing acceleration process. We substantiate our claim by the calculated behaviour of charge states corresponding to energized ions while they are accelerated in the source regions. These computations are based on the electron capture and loss cross sections. Results from the analysis allow us to conclude that, contrary to the general assumption, charge exchange processes may be invoked during the acceleration of energized ions in solar flares.

The Helium Valley: Comparison of Impulsive Solar Flare Ion Abundances and Gyroresonant Acceleration with Oblique Turbulence in a Hot Multi‐Ion Plasma

We present a detailed interpretation of the heavy ion abundance enhancements observed in impulsive —are energetic particles, in terms of the conditions for gyroresonant acceleration by moderately oblique waves in a hot solar coronal plasma. On the basis of a realistic coronal plasma containing its complete set of minor ions, we analyze —rst all parallel wave modes in terms of their dispersion relation, damping timescale, and condition for gyro- resonant acceleration of thermal ions, as a function of temperature. We identify the ii Helium Valley,ˇˇ the region in the frequency-wavenumber plane of strong wave damping by thermal 4He'2 ions, as crucial for explaining the observed abundances: any ions with charge-to-mass ratio in the neighborhood of 0.5 cannot be accelerated preferentially, relative to 4He'2. Then solving the dispersion relation equation for oblique waves in a hot e-p-He plasma, we discuss this general class of waves in terms of polarization and damping timescale. For waves propagating at moderate angles to the magnetic —eld our calculations indicate that the —rst harmonic n 1 ( hB / 90i), gyroresonance is dominant, and that the corresponding He valley narrows down for increasing angle h. Using this analysis, we calculate the limits of the He valley and investigate the preferential gyroresonant acceleration of heavy ions by moderately oblique waves in a solar coronal plasma. Only for ( hB / 90i) nearly perpendicular waves ( hB 90i), are higher order resonances important and regions of wave damping by interaction with thermal particles vanishingly narrow in frequency. We estimate the fraction of ions of each element outside the He valley as a function of temperature and compare the resulting enhanced abundances with the observed enhancements, for the case of a spec- trum of nonquasi-perpendicular waves, as produced by a cascading of the general turbulence. The results allow us to specify the range of possible temperatures for the source plasma of the accelerated particles to between D2.4 and D4.5 ) 106 K, i.e., comparable to active region (AR), but not to —aring gas, temperatures. This points to an acceleration of the ions taking place, either in the AR gas surround- ing the —are itself or within the —aring loop but before it became heated. Constraints are set on the typical time *t over which the ions are accelerated preferentially. We —nd times between D5 ) 10~4 and D3 ) 10~2 s (for our nominal plasma with density and —eld of

DC Electric Field Acceleration of Ions in Solar Flares

view Abstract Citations (34) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS DC Electric Field Acceleration of Ions in Solar Flares Holman, Gordon D. Abstract It is shown that the seed particles required for solar flare energetic particles and γ-ray bursts can be generated through the DC electric field acceleration of thermal ions. For an electric field strength on the order of but less than the Dreicer field (the critical field strength above which the entire electron distribution is in the runaway regime), a significant fraction of the thermal ions is accelerated up to a velocity in the range 0.1-1 υthe where υthe is the electron thermal velocity (giving ion energies up to 10-1000 keV nucleon-1). These ions are then available for additional acceleration by waves, or may be further accelerated in the current channels themselves if the electric field exceeds the Dreicer field. Heavier ions are found to have lower thresholds for runaway acceleration than protons and are therefore expected to have enhanced abundances at the energies to which they are accelerated. Under the conditions required for proton acceleration, the entire population of ions more massive than lithium is accelerated up to the electron drift velocity. Publication: The Astrophysical Journal Pub Date: October 1995 DOI: 10.1086/176316 Bibcode: 1995ApJ...452..451H Keywords: ACCELERATION OF PARTICLES; PLASMAS; SUN: FLARES; SUN: X-RAYS; GAMMA RAYS full text sources ADS |

Lower hybrid resonance acceleration of electrons and ions in solar flares and the associated microwave emission

view Abstract Citations (52) References (67) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Lower Hybrid Resonance Acceleration of Electrons and Ions in Solar Flares and the Associated Microwave Emission McClements, K. G. ; Bingham, R. ; Su, J. J. ; Dawson, J. M. ; Spicer, D. S. Abstract The particle acceleration processes here studied are driven by the relaxation of unstable ion ring distributions; these produce strong wave activity at the lower hybrid resonance frequency which collapses, and forms energetic electron and ion tails. The results obtained are applied to the problem posed by the production of energetic particles by solar flares. The numerical simulation results thus obtained by a 2 1/2-dimensional particle-in-cell code show a simultaneous acceleration of electrons to 10-500 keV energies, and of ions to as much as the 1 MeV range; the energy of the latter is still insufficient to account for gamma-ray emission in the 4-6 MeV range, but furnish a seed population for further acceleration. Publication: The Astrophysical Journal Pub Date: May 1993 DOI: 10.1086/172679 Bibcode: 1993ApJ...409..465M Keywords: Electron Acceleration; Ion Temperature; Microwave Emission; Resonant Frequencies; Solar Electrons; Solar Flares; Energy Transfer; Gamma Rays; Solar Atmosphere; Solar X-Rays; Solar Physics; ACCELERATION OF PARTICLES; SUN: FLARES; SUN: X-RAYS; GAMMA RAYS; SUN: PARTICLE EMISSION; SUN: RADIO RADIATION full text sources ADS |

The acceleration of electrons and ions in solar flares

We find that gamma-ray line (GRL) emissions start later than the hard X-ray (HXR) emissions during impulsive and extended solar flares. Starting delay is more in the case of extended solar flares suggesting a slow acceleration of electrons and ions, in comparison to impulsive solar flares which indicate different acceleration mechanism for impulsive and extended solar flares. We further infer that during solar flares, electrons and ions are accelerated simultaneously and the delay between HXR and GRL emissions results mainly due to differences in acceleration times of electrons and ions to attain energies required for producing HXR emissions for electrons and GRL emissions for ions. Therefore, we are of view that a single step acceleration mechanism may work in solar flares.

Electron Beam Diagnostics in Radiation from H- and He-like Ions in Solar Flares

view Abstract Citations (14) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Electron Beam Diagnostics in Radiation from H- and He-like Ions in Solar Flares Laming, J. M. Abstract The Lyα doublet in various hydrogenic ions has been observed previously in solar flares. Deviations in the intensity ratio from that expected on statistical grounds are interpreted here as arising from excitation of the ions by electrons in a beam. Such directed excitation leads to selective population of magnetic sublevels in the upper level, and hence to the emission of polarized and anisotropic radiation. The effects of such an electron beam on the ionization balance for Mg, and on line intensity ratios in He-like systems commonly used as diagnostics for the electron temperature, are also discussed. Publication: The Astrophysical Journal Pub Date: July 1990 DOI: 10.1086/168914 Bibcode: 1990ApJ...357..275L Keywords: RADIATION MECHANISMS; SUN: FLARES full text sources ADS |

Anisotropy of shock‐accelerated ion distributions in interplanetary space

Recent reports of energetic particles upstream of interplanetary shocks have concentrated upon the ability of the shocks to accelerate a small percentage of the solar wind thermal ion population. In keeping with the diffusive shock acceleration model, Lee (1983) derived a theory which predicts the asymptotic steady state approached by the energetic particle distribution and low‐frequency wave spectra upstream of interplanetary traveling shocks. More recently, Kennel et al. (1986) have performed a detailed test of the Lee theory by applying it to the observations of the November 12, 1978 shock viewed by the ISEE spacecraft. A major point of departure between the theory and observations rests with the spatial dependence of the particle intensity and anisotropy in the upstream region. We argue that this discrepancy is due to the presence of solar flare particles. These particles form an additional seed population which alters the upstream boundary condition of the energetic population. The resulting anisotropy of the energetic particle distribution several scale lengths upstream of the shock is proportional to the ratio of the streaming of the shock‐accelerated population to the density of the solar flare population. Comparison of this theoretical result with the observed upstream anisotropy suggests that the measured upstream anisotropies are due largely to the streaming of the solar flare ion population. We also compare this theory to the measured particle intensities and anisotropies in the April 4–5, 1979 shock event reported by Sanderson et al. (1985b) and conclude that very little of the upstream particle anisotropy measured for this event can be attributed to the shock acceleration process. Since energetic storm particle (ESP) events at 1 AU are frequently observed in association with solar flare particles, it is anticipated that the discussion presented here should describe a commonly observed aspect of ESP events.

Shock acceleration of electrons and ions in solar flares

The simultaneous first-order Fermi shock acceleration of electrons, protons, and alpha particles are compared to observations of solar energetic particle events. For each event, a unique shock compression ratio in the range of approximately 1.6-3 produces spectra in good agreement with observation. The range in compression ratios predicts that the more than five orders of magnitude spread in electron-to-proton intensity ratios observed at MeV energies is compressed to about three orders of magnitude at an assumed injection energy of 100 keV. The remaining spread can be accounted for with a modest range of injection conditions. The model predicts that the acceleration time to a given energy will be approximately equal for electrons and protons, and for reasonable solar parameters, can be on the order of 1 s to approximately 100 MeV. 37 references.

Turbulent heating in solar cosmic-ray theory

view Abstract Citations (16) References (9) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Turbulent heating in solar cosmic-ray theory Weatherall, J. Abstract The heating of minor ions in solar flares by wave-wave-particle interaction with Langmuir waves, or ion acoustic waves, can be described by a diffusion equation in velocity-space for the particle distribution function. The dependence of the heating on the ion charge and mass, and on the composition of the plasma, is examined in detail. It is found that the heat mechanisms proposed by Ibragimov and Kocharov cannot account for the enhanced abundances of heavy elements in the solar cosmic rays. Publication: The Astrophysical Journal Pub Date: June 1984 DOI: 10.1086/162119 Bibcode: 1984ApJ...281..468W Keywords: Solar Cosmic Rays; Solar Flares; Turbulent Heat Transfer; Distribution Functions; Heating Equipment; Heavy Elements; Solar Physics full text sources ADS |

On the E-W asymmetry and the generation of ESP events

Observations of energetic-ion intensity enhancements (E ≥ 290 keV) associated with solar flare generated shock waves (solar flare ESP events), obtained during nearly a decade by the APL/JHU instruments on board the Earth orbiters IMP-7 and 8, are incorporated in this work in order to examine the role of the heliolongitude depended large scale shock morphology with relation to the upstream interplanetary magnetic field in the formation of these ESP events. It is shown that a clear east-west solar hemisphere asymmetry is present in the distribution of the ESP relative intensity enhancements with respect to the heliolongitudes of the shock wave source-flare sites. The large ion-intensity enhancements superimposed on the ambient solar flare ion population are preferentially associated with solar flare sites located to the east of the spacecraft meridian, whereas on the average only weak ESP events are associated with solar flare sites to the west of the spacecraft meridian. The observed asymmetry and its implications on the dominant processes for the generation of the solar flare ESP events are discussed on the basis of the presented extensive survey.