Fast variations in high-energy X-rays from solar flares and their constraints on nonthermal models

Kiplinger, A. L.; Dennis, B. R.; Frost, K. J.; Orwig, L. E.

doi:10.1086/184408

Cited by 68 publications

(42 citation statements)

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“…This yields a 3 He= 4 He41 for small times t5 t 0 , 3 He= 4 He $ 0:1 1 for t 0 $ 0:63 0:89 s, and asymptotically approaches the coronal abundance ratio for times t4t 0 . The derived time range of t 0 corresponds well to the typical timescale of electron acceleration during the impulsive phases of flares of 0.1-1 s as manifest by the shortest hard X-ray peaks (Kiplinger et al 1984). Since the EF wave field is a direct consequence of the electron acceleration process, the lifetime of the field is expected to be on the same order of magnitude.…”

Section: Abundance Enhancementssupporting

confidence: 64%

Acceleration and Enrichment of³He in Impulsive Solar Flares by Electron Firehose Waves

Paesold

Kallenbach

Benz

2003

ApJ

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A new mechanism for acceleration and enrichment of 3 He during impulsive solar flares is presented. Lowfrequency electromagnetic plasma waves excited by the electron firehose instability (EFI) can account for the acceleration of ions up to 1 MeV amu À1 energies as a single-stage process. The EFI arises as a direct consequence of the free energy stored in a temperature anisotropy (T e k > T e ? ) of the bulk energized electron population during the acceleration process. In contrast to other mechanisms that require special plasma properties, the EFI is an intrinsic feature of the acceleration process of the bulk electrons. Being present as a side effect in the flaring plasma, these waves can account for the acceleration of 3 He and 4 He while selectively enhancing 3 He as a result of the spectral energy density built up from linear growth. Linearized kinetic theory, analytic models, and test particle simulations have been applied to investigate the ability of the waves to accelerate and fractionate. As waves grow in both directions parallel to the magnetic field, they can trap resonant ions and efficiently accelerate them to the highest energies. Plausible models have been found that can explain the observed energies, spectra, and abundances of 3 He and 4 He.

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Section: Abundance Enhancementssupporting

confidence: 64%

Acceleration and Enrichment of³He in Impulsive Solar Flares by Electron Firehose Waves

Paesold

Kallenbach

Benz

2003

ApJ

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“…The cyclic behavior of the solar large-scale magnetic field has, however, provided invaluable information about the physical processes involved and therefore the interest in finding additional periods is large. Since the discovery of the Rieger period around 155 days in the occurrence of high-energetic flares and Tables 4-6 are only available in electronic form at http://www.edpsciences.org (Rieger et al 1984;Kiplinger et al 1984;Bogart & Bai 1985), extensive investigations have been carried out to search for intermediate periodicities in the range between 27 days and 11 years in various solar activity indices (cf. Bai 2003b, and references therein).…”

Section: Introductionmentioning

confidence: 99%

Evolution and rotation of large-scale photospheric magnetic fields of the Sun during cycles 21–23

Knaack¹,

Stenflo

Berdyugina

2005

A&A

120

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Abstract. We present the results of an extensive time series analysis of longitudinally-averaged synoptic maps, recorded at the National Solar Observatory (NSO/Kitt Peak) from 1975 to 2003, and provide evidence for a multitude of quasi-periodic oscillations in the photospheric magnetic field of the Sun. In the low frequency range, we have located the sources of the 3.6 yr, 1.8 yr, and 1.5 yr periodicities that were previously detected in the north-south asymmetry of the unsigned photospheric flux (Knaack et al. 2004, A&A, 418, L17). In addition, quasi-periodicities around 2.6 yr and 1.3 yr have been found. The 1.3 yr period is most likely related to large-scale magnetic surges toward the poles and appeared in both hemispheres at intermediate latitudes ∼30• -55• during the maxima of all three cycles 21-23, being particularly pronounced during cycle 22. Periods near

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“…Particles are accelerated at many sites throughout the universe but solar flares offer the widest range of observations and allow to probe both, electron and ion acceleration. During solar flares, large amounts of energies (∼10 28 to ∼10 34 erg) are released on time scales varying from fractions of seconds to minutes (Kiplinger et al 1984). The magnitude and energy spectrum in hard X-rays often indicate that much of the released energy goes into the energization of electrons at tens of keV and can extend up to 10 MeV.…”

Section: Introductionmentioning

confidence: 99%

Test particle simulation of the Electron Firehose instability

Paesold

Benz

2003

A&A

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Abstract. In the course of the energization of electrons to energies of some tens of keV during the impulsive phase of a solar flare, the velocity distribution function of the electrons is predicted to become anisotropic with T e > T e ⊥ (Here, and ⊥ denote directions with respect to the background magnetic field). Such a configuration can become unstable to the so-called Electron Firehose instability (EFI). Left hand circularly polarized electromagnetic waves propagating along the magnetic field are excited via a non-resonant mechanism: electrons non-resonantly excite the waves while the protons are in resonance and carry the wave. The non-resonant nature of the instability raises the question of the response of the electron population to the growing waves. Test particle simulations are carried out to investigate the pitch-angle development of electrons injected to single waves and wave spectra. To interpret the simulation results, a drift kinetic approach is developed. The findings in the case of single wave simulations show the scattering to larger pitch-angles in excellent agreement with the theory. The situation dramatically changes when assuming a spectrum of waves. Stochasticity is detected at small initial parallel velocities resulting in significant deviations from drift kinetic theory. It enhances the scattering rate of electrons with initial parallel velocity below to the mean thermal perpendicular velocity. Increased scattering is also noticed for electrons having initial parallel velocity within an order of magnitude of the resonance velocity. The resulting pitch-angle scattering is proposed to be an important ingredient in Fermi-type electron acceleration models, particularly transit-time acceleration by compressional MHD waves.

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Fast variations in high-energy X-rays from solar flares and their constraints on nonthermal models

Cited by 68 publications

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Acceleration and Enrichment of³He in Impulsive Solar Flares by Electron Firehose Waves

Acceleration and Enrichment of³He in Impulsive Solar Flares by Electron Firehose Waves

Evolution and rotation of large-scale photospheric magnetic fields of the Sun during cycles 21–23

Test particle simulation of the Electron Firehose instability

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Fast variations in high-energy X-rays from solar flares and their constraints on nonthermal models

Cited by 68 publications

References 0 publications

Acceleration and Enrichment of3He in Impulsive Solar Flares by Electron Firehose Waves

Acceleration and Enrichment of3He in Impulsive Solar Flares by Electron Firehose Waves

Evolution and rotation of large-scale photospheric magnetic fields of the Sun during cycles 21–23

Test particle simulation of the Electron Firehose instability

Contact Info

Product

Resources

About

Acceleration and Enrichment of³He in Impulsive Solar Flares by Electron Firehose Waves

Acceleration and Enrichment of³He in Impulsive Solar Flares by Electron Firehose Waves