共查询到20条相似文献，搜索用时 593 毫秒
1.
Zahra Bagheri Pantea Davoudifar Gohar Rastegarzadeh Milad Shayan 《Journal of Astrophysics and Astronomy》2017,38(1):4
In this paper, we used CORSIKA code to understand the characteristics of cosmic ray induced showers at extremely high energy as a function of energy, detector distance to shower axis, number, and density of secondary charged particles and the nature particle producing the shower. Based on the standard properties of the atmosphere, lateral and longitudinal development of the shower for photons and electrons has been investigated. Fluorescent light has been collected by the detector for protons, helium, oxygen, silicon, calcium and iron primary cosmic rays in different energies. So we have obtained a number of electrons per unit area, distance to the shower axis, shape function of particles density, percentage of fluorescent light, lateral distribution of energy dissipated in the atmosphere and visual field angle of detector as well as size of the shower image. We have also shown that location of highest percentage of fluorescence light is directly proportional to atomic number of elements. Also we have shown when the distance from shower axis increases and the shape function of particles density decreases severely. At the first stages of development, shower axis distance from detector is high and visual field angle is small; then with shower moving toward the Earth, angle increases. Overall, in higher energies, the fluorescent light method has more efficiency. The paper provides standard calibration lines for high energy showers which can be used to determine the nature of the particles. 相似文献
2.
Krzysztof Stasiewicz 《Planetary and Space Science》1985,33(6):591-596
The influence of low-frequency electrostatic turbulence on the flux of precipitating magnetospheric electrons is analyzed in the framework of the quasilinear kinetic equation. It is shown that an electron population in a turbulent region, with an electric field parallel to the ambient magnetic field, can be separated into two parts by introducing a pitch angle dependent runaway velocity vr(θ). Lower energy electrons with parallel velocity v∥ < vr are effectively scattered by plasma waves, so that they remain in the main population and are subjected to an anomalous transport equation. A distribution function f ∞ v?4 (or the particle flux vs energy J ∞ E?1) is established in this velocity range. Faster electrons with v∥ ? vr are freely accelerated by a parallel electric field, so that they contribute directly to hot electron fluxes which are observed at ionospheric altitudes. New expressions are derived for the magnetic-field aligned current and the electron energy flux implied by this model. These expressions agree well with empirical relations observed in auroral inverted-V structures. 相似文献
3.
《New Astronomy》2013
In this study we investigate the pure cyclotron spectra of an Intermediate Polar (IP), V405 Aur, which has the highest magnetic field strength in its class. Recent studies have shown that cyclotron harmonics are seen in the spectra of V405 Aur. We assume that cyclotron harmonics are produced by electrons having a streaming bi-Maxwellian velocity profile found in the lower portions of the accretion column connecting to the magnetic poles of the white dwarf in V405 Aur system. Then we applied the Green function for a dispersive medium such as the one found in V405 Aur. Further we assume that the cyclotron radiation is produced at Ordinary and Extraordinary wave modes. We find the general solution of the Green function for the Extraordinary wave mode and a dispersive medium and we derived the pure cyclotron spectra from the Green function. This function enabled us to calculate energy radiated per unit wavelength per unit solid angle as a function of wavelength which revealed the sixth, seventh and the eighth harmonics which correspond to the observed values. Our model produces the observed cyclotron spectrum of V405 Aur. 相似文献
4.
The resonant interaction between the whistler mode waves and the energetic electrons near the plasmapause boundary has been studied in the presence of field aligned currents which seem to exist during substorm activity. It is shown that the electrons which carry the current along the direction of the magnetic field enhance the whistler mode growth considerably if the streaming velocity is small compared to the phase velocity of the wave. It is likely that this is one of the mechanisms explaining the intense VLF emissions observed near the plasmapause during substorm activity. 相似文献
5.
Mingalev O. V. Khabarova O. V. Malova Kh. V. Mingalev I. V. Kislov R. A. Mel’nik M. N. Setsko P. V. Zelenyi L. M. Zank G. P. 《Solar System Research》2019,53(1):30-55
Crossings of the heliospheric current sheet (HCS) at the Earth’s orbit are often associated with observations of anisotropic beams of energetic protons accelerated to energies from hundreds of keV to several MeV and above. A connection between this phenomenon and the occurrence of small-scale magnetic islands (SMIs) near reconnecting current sheets has recently been found. This study shows how pre-accelerated protons can be energized additionally due to oscillations of multiple SMIs inside the ripple of the reconnecting HCS. A model of the electromagnetic field of an oscillating 3D SMI with a characteristic size of ~0.001 AU is developed. A SMI is supposed to be bombarded by protons accelerated by magnetic reconnection at the HCS to energies from ~1keV to tens of keV. Numerical simulations have demonstrated that the resulting longitudinal inductive electric fields can additionally reaccelerate protons injected into a SMI. It is shown that there is a local “acceleration” region within the island in which particles gain energy most effectively. As a result, their average escape energies range from hundreds of keV to 2 MeV and above. There is almost no particle acceleration outside the region. It is shown that energies gained by protons significantly depend on the initial phase and the place of their entry into a SMI but weakly depend on the initial energy. Therefore, low-energy particles can be accelerated more efficiently than high-energy particles, and all particles can reach the total energy limit upon their escape from a SMI. It is also found that the escape velocity possesses a strong directional anisotropy. The results are consistent with observations in the solar wind plasma.
相似文献6.
Dean F. Smith 《Solar physics》1980,66(1):135-148
Requirements for the number of nonthermal electrons which must be accelerated in the impulsive phase of a flare are reviewed. These are uncertain by two orders of magnitude depending on whether hard X-rays above 25 keV are produced primarily by hot thermal electrons which contain a small fraction of the flare energy or by nonthermal streaming electrons which contain > 50% of the flare energy. Possible acceleration mechanisms are considered to see to what extent either X-ray production scenario can be considered viable. Direct electric field acceleration is shown to involve significant heating. In addition, candidate primary energy release mechanisms to convert stored magnetic energy into flare energy, steady reconnection and the tearing mode instability, transfer at least half of the stored energy into heat and most of the remaining energy to ions. Acceleration by electron plasma waves requires that the waves be driven to large amplitude by electrons with large streaming velocities or by anisotropic ion-acoustic waves which also require streaming electrons for their production. These in turn can only come from direct electric field acceleration since it is shown that ion-acoustic waves excited by the primary current cannot amplify electron plasma waves. Thus, wave acceleration is subject to the same limitations as direct electric field acceleration. It is concluded that at most 0.1% of the flare energy can be deposited into nonthermal streaming electrons with the energy conversion mechanisms as they have been proposed and known acceleration mechanisms. Thus, hard X-ray production above 10 keV primarily by hot thermal electrons is the only choice compatible with models for the primary energy release as they presently exist. 相似文献
7.
8.
C. C. Harvey 《Solar physics》1975,40(1):193-216
In an earlier paper (Harvey and Aubier, 1973) the large scale radial electron density gradient in the corona and solar wind was shown to cause the phase velocity of plasma waves to decrease as they propagate away from the Sun, thus leading to appreciable Landau damping of the plasma waves. It is proposed here that this same phase velocity decrease creates conditions which facilitate the stabilisation of a beam of exciter electrons of finite duration, provided that three conditions are fulfilled. Two of these conditions concern the velocity-time distribution of the exciter electrons at their point of ejection from the Sun, while the third is simply that, above a certain altitude, the coronal electron density decreases with altitude r faster than r ?2. The plasma wave source is then associated with the leading edge of the electron stream. The spatial density of the power converted into plasma waves is calculated as a function of position and time, and is shown to be independent of the nature of the stabilisation mechanism. The maximum of this power density is found to move outwards from the Sun at a uniform speed when a simple electron injection model with a Maxwellian velocity distribution is introduced. 相似文献
9.
Recent results of the gamma-ray Cherenkov astronomy definitely prove the existence of fast variability in the very high energy
(V.H.E.) gamma-ray flux of some active galactic nuclei. The BL Lac PKS 2155-304 for instance showed variations down to a few
minutes time scale. From standard light travel time argument, these variations put extremely strong constraints on the size
of the TeV emitting zone, which has to be of the order of a few Schwarzschild radius, even for high values of the relativistic
Doppler factor of the emitting jets. Such discovery is a challenge for particle acceleration scenarios, which have to imagine
efficient acceleration processes at work in a very compact zone. Eventually, the immediate vicinity of the central black hole
appears as the most conservative choice for the location of the TeV emission region of active galactic nuclei. In this paper,
we propose a two-step mechanism for charged particle acceleration in the magnetosphere of a massive black hole surrounded
by an accretion disk. Particles first gain energy by a stochastic process during the accretion phase. It is shown that effective
proton acceleration up to energies 1017–1019 eV is possible in a low-luminosity magnetized accretion disk with 2D turbulent motion. The distribution function of energetic
protons over energies is a power law function with typical index ≃−1. Here electrons are not very efficiently accelerated
because of their drastic losses by synchrotron radiation. In a second time, part of the fast particles escape from the disk
and are then entrained by the magnetic structure above the disk, in the rotating black hole magnetosphere. They thus gain
additional energy by direct centrifugal mechanism, up to about 1020 eV for the protons and to 10–100 TeV for the electrons when they cross the light cylinder surface. Such energetic particles
can further radiate in the TeV spectral range observed by Cherenkov experiments as HESS, MAGIC and VERITAS. Energetic protons
can produce γ-radiation in the energy band 1 GeV–100 TeV and above mainly by nuclei collisions with the disk matter, clouds, or ambient
low energy photons. Energetic electrons can also reach the required spectral range by inverse Compton emission. However their
acceleration is less efficient due to heavy radiation losses, and only gained by centrifugal process during the second phase
of the whole mechanism we describe. Our present analysis would therefore favor hadronic scenarios for TeV emission of active
galactic nuclei. It is tempting to relate long term variability over years of TeV active galactic nuclei to the first stochastic
acceleration phase, which also provides the needed power law particle distributions, while short term variability over minutes
is more likely due to perturbations of the second fast direct acceleration phase. 相似文献
10.
The energetics of the excitation of the Farley-Buneman instability is considered, which is recently observed in the auroral and equatorial E regions of the Earth's ionosphere at altitudes between 100 km and 120 km. In the magnetic field of the Earth the Farley-Buneman instability is excited under the condition of a strong enough external electric field in the case of ion-neutral collisions with frequencies much larger than the ion gyrofrequency and electron-neutral collisions with frequencies much below the electron gyrofrequency. It is shown that the linear increase of the wave amplitudes is caused by a small disbalance between the processes of nonlinear energy pumping into the wave from an external electric field and the energy loss because of the collisions of the electrons and ions with the neutral particles. During the nonlinear energy pumping energy of the external electric field is transferred into a nonlinear current of second order, which is connected with the oscillating motion of the electrons in the wave. The oscillating electron motion takes place perpendicular to wave propagation. From the estimations follows that the energy pumped into a Farley-Buneman wave during one period of pulsation is much larger than the wave energy itself. A new and simply to understand derivation of the anomalous diffusion coefficient is presented, related to the study of the behaviour of a test wave with frequency much above the frequencies of the Farley-Buneman turbulence in developed stage can cause an additional macroscopic nonlinear Pedersen current directed along the external electric field. It is found that the nonlinear Pedersen current can reach the order of the usual Pedersen current and should contribute to the effective heating of the ionospheric plasma. 相似文献
11.
Heating and acceleration of electrons in solar impulsive hard X-ray (HXR) flares are studied according to the two-stage acceleration model developed by Zhang for solar 3He-rich events. It is shown that electrostatic H-cyclotron waves can be excited at a parallel phase velocity less than about the electron thermal velocity and thus can significantly heat the electrons (up to 40 MK) through Landau resonance. The preheated electrons with velocities above a threshold are further accelerated to high energies in the flare-acceleration process. The flare-produced electron spectrum is obtained and shown to be thermal at low energies and power law at high energies. In the non-thermal energy range, the spectrum can be double power law if the spectral power index is energy dependent or related. The electron energy spectrum obtained by this study agrees quantitatively with the result derived from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) HXR observations in the flare of 2002 July 23. The total flux and energy flux of electrons accelerated in the solar flare also agree with the measurements. 相似文献
12.
We analyze particle acceleration processes in large solar flares, using observations of the August, 1972, series of large events. The energetic particle populations are estimated from the hard X-ray and γ-ray emission, and from direct interplanetary particle observations. The collisional energy losses of these particles are computed as a function of height, assuming that the particles are accelerated high in the solar atmosphere and then precipitate down into denser layers. We compare the computed energy input with the flare energy output in radiation, heating, and mass ejection, and find for large proton event flares that:
- The ～10–102 keV electrons accelerated during the flash phase constitute the bulk of the total flare energy.
- The flare can be divided into two regions depending on whether the electron energy input goes into radiation or explosive heating. The computed energy input to the radiative quasi-equilibrium region agrees with the observed flare energy output in optical, UV, and EUV radiation.
- The electron energy input to the explosive heating region can produce evaporation of the upper chromosphere needed to form the soft X-ray flare plasma.
- Very intense energetic electron fluxes can provide the energy and mass for interplanetary shock wave by heating the atmospheric gas to energies sufficient to escape the solar gravitational and magnetic fields. The threshold for shock formation appears to be ～1031 ergs total energy in >20 keV electrons, and all of the shock energy can be supplied by electrons if their spectrum extends down to 5–10 keV.
- High energy protons are accelerated later than the 10–102 keV electrons and most of them escape to the interplanetary medium. The energetic protons are not a significant contributor to the energization of flare phenomena. The observations are consistent with shock-wave acceleration of the protons and other nuclei, and also of electrons to relativistic energies.
- The flare white-light continuum emission is consistent with a model of free-bound transitions in a plasma with strong non-thermal ionization produced in the lower solar chromosphere by energetic electrons. The white-light continuum is inconsistent with models of photospheric heating by the energetic particles. A threshold energy of ～5×1030 ergs in >20 keV electrons is required for detectable white-light emission.
13.
Loukas Vlahos 《Solar physics》1987,111(1):155-166
Energetic electrons, with energies 10–100 keV, accelerated during the impulsive phase of solar flares, sometimes encounter increasing magnetic fields as they stream towards the chromosphere. A consequence of the conservation of their magnetic moment is that the electrons with large initial pitch angle will be reflected at different heights from the atmosphere. Energetic electrons reflected below the transition zone will lose most of their energy to collisions and will never return to the corona. Thus, electrons reflected above the transition zone form a loss-cone velocity distribution which can be unstable to Electron Cyclotron Maser (ECM). The interaction of quasi-perpendicular shocks with the ambient coronal plasma will form a ‘ring’ or ‘hollow beam’ velocity distribution upstream of the shock. ‘Ring’ velocity distributions are also unstable to the ECM instability. A review of the recent results on the theory of ECM will be presented. We will focus our discussion on the questions: (a) What are the characteristics of the linear growth rate of the ECM during solar flares? (b) How does the ECM saturate and what is its efficiency? (c) How does the ECM generated radiation modify the flare environment? Finally we will review the outstanding questions in the theory of ECM and we will relate the theoretical predictions to current observations. 相似文献
14.
I. Lerche 《Astrophysics and Space Science》1979,63(1):79-102
Using the geometrical optics approximation, we give the behavior of fast and slow magneto-ionic rays passing through a plasma which possesses a differential shear. Depending upon the orientation of the ambient magnetostatic field with respect to the flow direction, it is shown that the effects of the shear can cause ray paths to propagateupstream ordownstream. The fact that in an homogeneous plasma the slow magneto-ionic wave has a group angle which is oppositely directed to its phase angle causes the slow rays to exhibit properties which are extremely curious relative to those obtaining for the fast rays — which are themselves interesting. We have done these calculations to show that the effects of velocity shear in an otherwise homogeneous plasma lead to interesting ray behaviors which, presumably, bear upon the more general question of magneto-ionic energy transport in inhomogeneous plasmas. 相似文献
15.
Using a 2 1/2-D fully relativistic electromagnetic particle-in-cell code (PIC) we have investigated a potential electron acceleration mechanism in solar flares. The free energy is provided by ions which have a ring velocity distribution about the magnetic field direction. Ion rings may be produced by perpendicular shocks, which could in turn be generated by the super-Alfvénic motion of magnetic flux tubes emerging from the photosphere or by coronal mass ejections (CMEs). Such ion distributions are known to be unstable to the generation of lower hybrid waves, which have phase velocities in excess of the electron thermal speed parallel to the field and can, therefore, resonantly accelerate electrons in that direction. The simulations show the transfer of perpendicular ion energy to energetic electrons via lower hybrid wave turbulence. With plausible ion ring velocities, the process can account for the observationally inferred fluxes and energies of non-thermal electrons during the impulsive phase of flares. Our results also show electrostatic wave generation close to the plasma frequency: we suggest that this is due to a bump-in-tail instability of the electron distribution. 相似文献
16.
It has recently been shown that adiabatic solutions of the one-dimensional current sheet problem exist provided that magnetically trapped particles are included in the model together with the current-carrying untrapped “beam” particles. We show here that a formulation of the problem in terms of particle velocity and pitch angle is advantageous, and we derive some general properties of the solutions. In particular it is shown that there is, in general, no discontinuity in the value of the particle distribution function ? across the boundary in velocity space between “beam” and trapped particles, but that there will be a discontinuity in the gradients of ?. An example is given in which the beam population is of bi-Maxwellian form at the outer boundary of the current sheet. 相似文献
17.
《Icarus》1987,71(1):78-90
It is shown that a particle ring with energy dissipation has an extremum in its energy when all the particles are in the same circular orbit. This extremum is a relative maximum in radial directions, indicating possible radial expansion; but it is a relative minimum in the particle velocity components, indicating a tendency for the velocity distribution to collapse. An N-body model of ring evolution incorporating two-body dynamics, oblateness perturbations, inelastic collisions, and phase averaging is described. By local analysis of impact statistics, it is shown that the velocity distribution of the ring will collapse if the coefficient of restitution ∈ ≲ 0.7. The collapse of the velocity distribution stabilizes a ring of point particles against radial dispersion. Furthermore, for ∈ ≲ 0.25, the semimajor axis distribution tends to collapse toward its local mean value, leading to radial collapse. A survey of ring evolution is presented for different values of coefficient of restitution and initial velocity dispersion. As has been predicted uy Goldreich and Tremaine, rings with equilibrium velocity distributions are unstable and expand, while rings where the velocity distribution collapses are shown to undergo massive, pervasive fragmentation into a myriad of ringlets. It is proposed that such fragmented rings are stable in their own right, and that the observational test to discriminate between the two cases is simply the presence of a smooth, featureless surface or the presence of intricate radial structure in the ring. 相似文献
18.
M.K. Bird 《Planetary and Space Science》1975,23(1):27-40
Low-energy particle trajectories in an idealized magnetotail magnetic field are investigated to determine the accessibility of magnetosheath protons and electrons to the plasma sheet along the flanks of the tail magnetopause. The drift motion of the positively (negatively) charged particles incident on the dawn (dusk) magnetotail flank causes such particles to penetrate deeper into the magnetotail. For certain combinations of particle energy, incident velocity vector and initial penetration point on the tail magnetopause, the incident particles can become trapped in the plasma sheet, after which their net drift motion then provides a current capable of supporting the entire observed magnetotail field. The results further indicate that the bulk of the solar wind plasma just outside the distant tail boundary, which streams preferentially in a direction along the magnetopause away from the Earth at velocities around 400 km s?1, can be caught up in the tail if the initial penetration point is within about 2RE, of the quasi-neutral sheet. It is suggested that a large fraction of the magnetotail plasma is composed of former solar wind particles which have penetrated the magnetospheric boundary at the tail flanks. 相似文献
19.
Acceleration of Electrons and Protons in Reconnecting Current Sheets Including Single or Multiple X-points 总被引：1，自引：0，他引：1
Kinematic characteristics of electrons and protons in the magnetic reconnecting current sheet in the presence of a guide field are investigated. Particle trajectories are calculated for different values of the guide field by a test-particle calculation. The relationship between the final energy and the initial position has also been studied. We found that the addition of a guide field not only allows particles to get more energy and not only results in the separation of electrons and protons, but also causes the reconnecting electric field to selectively accelerate electrons and protons for different initial positions. The energy spectrum eventually obtained is the common power-law spectrum, and as the guide field increases, the index for the spectrum of electrons decreases rapidly. However, for a weak background magnetic field, proton spectra are not very sensitive to the guide field; but for a strong background field, the dependence of the spectrum index is similar to the electron spectrum. Meanwhile, kinematic characteristics of the accelerated particles in the current sheet including multiple X-points and O-points were also investigated. The result indicates that the existence of the multiple X- and O-points helps particles trapped in the accelerating region to gain more energy, and yields the double or multiple power-law feature. 相似文献
20.
Using a kappa velocity distribution function for the electrons of the background plasma, the dynamics of a beam of hot electrons
streaming through the plasma and the generation of Langmuir waves are investigated in the frame work of quasilinear theory.
It is shown that the Langmuir waves are strongly damped by high energy tail of the Kappa distribution function. The spatial
expansion of the beam is reduced and the spectral density of Langmuir waves becomes narrower. The height of the plateau in
the beam distribution function increases at small velocities and the average velocity of beam is larger than that of a Maxwellian
distribution. The influence of Kappa velocity distribution function on the gasdynamical parameters is investigated. It is
found that, the height of plateau in the beam distribution function, and its lower velocity boundary are enhanced while, the
local beam width in velocity space decreases. 相似文献