共查询到20条相似文献，搜索用时 31 毫秒
1.
Yu. I. Fedorov 《Kinematics and Physics of Celestial Bodies》2011,27(1):1-16
Acceleration of cosmic rays interacting with the anisotropic magnetohydrodynamic turbulent medium is studied. Particle acceleration
is caused by a large-scale electric field arising in a turbulent medium due to the α-effect. A comparison is made of equilibrium
spectra of cosmic rays, characteristic of the specific acceleration mechanism, with the energy distribution of particles corresponding
to the statistical Fermi acceleration. 相似文献
2.
宇宙线的起源是高能天体物理的核心问题之一.一直以来,超新星爆发被认为是能谱膝区以下宇宙线的主要来源.多波段观测表明,超新星遗迹有能力加速带电粒子至亚PeV (10~(15)eV)能量.扩散激波加速被认为是最有效的天体高能粒子加速机制之一,而超新星遗迹的大尺度激波正好为这一机制提供平台.近年来,一系列较高精度的地面和空间实验极大地推动了对宇宙线以及超新星遗迹的研究.新的观测事实挑战着传统的扩散激波加速模型以及其在银河系宇宙线超新星遗迹起源学说上的应用,深化了人们对宇宙高能现象的认识.结合超新星遗迹辐射能谱的时间演化特性,构建的时间依赖的超新星遗迹粒子加速模型,不仅能够解释200 GV附近宇宙线的能谱反常,还自然地形成能谱膝区,甚至可以将超新星遗迹粒子加速对宇宙线能谱的贡献延伸至踝区.该模型预期超新星遗迹中粒子的输运行为表现为湍流扩散,这需要未来的观测以及与粒子输运相关的等离子体数值模拟工作来进一步验证. 相似文献
3.
《Chinese Astronomy and Astrophysics》2020,44(1):1-31
The origin of cosmic rays is one of the key questions in high-energy astrophysics. Supernovae have been always considered as the dominant sources of cosmic rays below the energy spectrum knee. Multi-wavelength observations indeed show that supernova remnants are capable for accelerating particles into sub-PeV (10 eV) energies. Diffusive shock acceleration is considered as one of the most efficient acceleration mechanisms of astrophysical high-energy particles, which may just operate effectively in the large-scale shocks of supernova remnants. Recently, a series of high-precision ground and space experiments have greatly promoted the study of cosmic rays and supernova remnants. New observational features challenge the classical acceleration model by diffusive shock and the application to the scenario of supernova remnants for the origin of Galactic cosmic rays, and have deepened our understanding to the cosmic high-energy phenomena. In combination with the time evolution of radiation energy spectrum of supernova remnants, a time-dependent particle acceleration model is established, which can not only explain the anomalies in cosmic-ray distributions around 200 GV, but also naturally form the cosmic-ray spectrum knee, even extend the contribution of supernova particle acceleration to cosmic ray flux up to the spectrum ankle. This model predicts that the high-energy particle transport behavior is dominated by the turbulent convection, which needs to be verified by future observations and plasma numerical simulations relevant to the particle transport. 相似文献
4.
S.V. Chalov 《Astrophysics and Space Science》2000,274(1-2):25-33
It is generally accepted that pick-up ions act as a seed population for anomalous cosmic rays originating at the solar wind
termination shock. We believe that the ion pre-acceleration process operating in the heliosphere up to the termination shock
can be very important to inject the ions into the shock acceleration process. The pick-up ions pre-accelerated by solar wind
turbulences have already a pronounced high energy tail when they reach the shock. Some fraction of these ions can experience
further acceleration up to energies of anomalous cosmic rays by means of shock drift and diffusive acceleration. In the present
paper the shock drift acceleration of pick-up ions suffering multiple reflection due to abrupt changes in both the strength
and direction of the magnetic field through the shock is considered. The reflection process operates for high velocity particles
different from the reflection by the electric cross-shock potential. During the first reflection the mean kinetic energy of
pick-up ions increases by approximately a factor of 10. Reflected particles have highly anisotropic velocity distribution.
Subsequent excursion of the particles in the turbulent upstream flow leads to diffusion in pitch-angle space and, as a result,
the particles can return to the shock again suffering, thus, multiple encounters. In order to describe the motion of particles
in the upstream and down streamparts of the flow we solve the Fokker-Plank transport equation for anisotropic velocity distribution
function.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
V. S. Ptuskin 《Astrophysics and Space Science》1979,61(2):259-265
A modification of the diffusional motion of cosmic rays in a large scale turbulent field is considered. The partial dragging of particles in the arbitrarily wandering magnetic field lines may lead to the creation of a new regime of diffusion of cosmic rays in the Galaxy. 相似文献
6.
Cosmic rays are ubiquitous in space, and the essential similarity of their energy spectra in many different regions places significant general constraints on the mechanisms for their acceleration and confinement. Diffusive shock acceleration is at present the most successful acceleration mechanism proposed, and, together with transport in Kolmogorov turbulence, can account for the universal specta. A unique laboratory for studying the acceleration and transport of charged particles is the outer heliosphere, including the solar wind termination shock and heliosheath.
A widely accepted paradigm for the transport and acceleration of energetic particles in the heliosphere has evolved over the last few decades. This picture has successfully explained many features of the modulation of galactic cosmic rays and the transport and acceleration of anomalous cosmic rays at the solar-wind termination shock. Recent Voyager observations near and beyond the termination shock have revealed new, and in some cases, unexpected phenomena which have led to questions concerning the established paradigm. The physical interpretation of the observations requires a blunt termination shock, rapid inward motion of the shock and temporal variations over time scales ranging from hours to 22 years. Incorporation of these into the physics has promise of explaining most, if not, all of the observed phenomena while retaining the advantages of the termination shock paradigm for both galactic and anomalous cosmic rays. 相似文献
7.
One dimensional numerical results of the non-linear interaction between cosmic rays and a magnetic field are presented. These
show that cosmic ray streaming drives large amplitude Alfvénic waves. The cosmic ray streaming energy is very efficiently
transfered to the perturbed magnetic field of the Alfvén waves. Thus a magnetic field of interstellar values, assumed in models
of supernova remnant blast wave acceleration, would not be appropriate in the region of the shock. The increased magnetic
field reduces the acceleration time and so increases the maximum cosmic ray energy, which may provide a simple and elegant
resolution to the highest energy galactic cosmic ray problem were the cosmic rays themselves provide the fields necessary
for their acceleration.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
One-, two- and three-dimensional numerical results of the non-linear interaction between cosmic rays and a magnetic field are presented. These show that cosmic ray streaming drives large-amplitude Alfvénic waves. The cosmic ray streaming energy is very efficiently transferred to the perturbed magnetic field of the Alfvén waves, and the non-linear time-scale of the growth of the waves is found to be very rapid, of the order of the gyro-period of the cosmic ray. Thus, a magnetic field of interstellar values, assumed in models of supernova remnant blast wave acceleration, would not be appropriate in the region of the shock. The increased magnetic field reduces the cosmic ray acceleration time and so increases the maximum cosmic ray energy, which may provide a simple and elegant resolution to the highest energy Galactic cosmic ray problem, where the cosmic rays themselves provide the fields necessary for their acceleration. 相似文献
9.
Stphane Coutu Steven W. Barwick James J. Beatty Amit Bhattacharyya Chuck R. Bower Christopher J. Chaput Georgia A. de Nolfo Michael A. DuVernois Allan Labrador Shawn P. McKee Dietrich Müller James A. Musser Scott L. Nutter Eric Schneider Simon P. Swordy Gregory Tarl Andrew D. Tomasch Eric Torbet 《Astroparticle Physics》1999,11(4):208-435
Galactic cosmic rays consist of primary and secondary particles. Primary cosmic rays are thought to be energized by first order Fermi acceleration processes at supernova shock fronts within our Galaxy. The cosmic rays that eventually reach the Earth from this source are mainly protons and atomic nuclei, but also include electrons. Secondary cosmic rays are created in collisions of primary particles with the diffuse interstellar gas. They are relatively rare but carry important information on the Galactic propagation of the primary particles. The secondary component includes a small fraction of antimatter particles, positrons and antiprotons. In addition, positrons and antiprotons may also come from unusual sources and possibly provide insight into new physics. For instance, the annihilation of heavy supersymmetric dark matter particles within the Galactic halo could lead to positrons or antiprotons with distinctive energy signatures. With the High-Energy Antimatter Telescope (HEAT) balloon-borne instrument, we have measured the abundances of positrons and electrons at energies between 1 and 50 GeV. The data suggest that indeed a small additional antimatter component may be present that cannot be explained by a purely secondary production mechanism. Here we describe the signature of the effect and discuss its possible origin. 相似文献
10.
We discuss the present status of our understanding of the transport and acceleration of anomalous cosmic rays and the transport
of galactic and CIR-accelerated particles in the heliosphere. Currently, two- and three-dimensional numerical codes can accurately
model many of the observed phenomena – with the major current uncertainties being the values of the parameters such as the
diffusion coefficients and the effects of the poorly understood structure beyond the termination shock. We illustrate the
nature of the phenomena by discussing in detail the response of energetic particles to co-rotating interaction regions, the
acceleration of singly- and multiply-charged anomalous cosmic rays, and the effects of galactic cosmic rays on the structure
of the solar wind and its termination shock.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
Stirling A. Colgate 《Solar physics》1988,118(1-2):1-15
High energy phenomena on the surface of the Sun are manifestations of part of the solar dynamo cycle. Convection and magnetic field give rise to unstable, twisted flux loops that become solar flares when the resistive tearing mode proceeds to the nonlinear limit. If such twisted flux loops did not dissipate rapidly due to an enhanced resistivity, then the dynamo would not work. The act of dissipation leads to intense heating and acceleration leading to X-rays and accelerated particles. The particles in turn give rise to hard X-rays, gamma rays, neutrons, and solar cosmic rays. In high-energy astrophysics such phenomena occur in accretion disks around compact objects like black holes in quasars and SS433. The resulting acceleration may explain the observed extremely high-energy cosmic rays of up to 1020 eV and the high-energy gamma rays of 1012 to 1015 eV. These high energies are more readily explained by acceleration E parallel to B as opposed to stochastic shock acceleration. The anisotropy and localization of gamma rays from solar flares potentially may indicate which mechanism is prevalent. 相似文献
12.
An interstellar medium consisting of regular and turbulent magnetic fields, thermal gas and cosmic rays is tested for stability in a stellar gravitational field. Cosmic rays are described by the diffusion-convection equation and the stability region of the system is determined. It is shown that the presence of cosmic rays is a stabilizing factor if the cosmic-ray diffusion coefficient is sufficiently small. The dependence of the maximum growth rate of instability on the cosmic-ray diffusion coefficient is qualitatively determined. 相似文献
13.
Recent direct measurements of the energy spectra of the major mass components of cosmic rays have indicated the presence of a ‘kink’ in the region of 200 GeV per nucleon. The kink, which varies in magnitude from one element to another, is much sharper than predicted by our cosmic ray origin model in which supernova remnants are responsible for cosmic ray acceleration and it appears as though a new, steeper component is responsible.The component amounts to about 20 percent of the total at 30 GeV/nucleon for protons and helium nuclei and its magnitude varies with nuclear charge; the unweighted fraction for all cosmic rays being 36%.The origin of the new component is subject to doubt but the contenders include O, B, A, supergiant and Wolf-Rayet stars, by way of their intense stellar winds. Another explanation is also in terms of these particles as the sources but then being trapped, and even further accelerated, in the Local Bubble. 相似文献
14.
On the escape of particles from cosmic ray modified shocks 总被引：1，自引：0，他引：1
D. Caprioli P. Blasi E. Amato 《Monthly notices of the Royal Astronomical Society》2009,396(4):2065-2073
Stationary solutions to the problem of particle acceleration at shock waves in the non-linear regime, when the dynamical reaction of the accelerated particles on the shock cannot be neglected, are known to show a prominent energy flux escaping from the shock towards upstream infinity. On physical grounds, the escape of particles from the upstream region of a shock has to be expected in all those situations in which the maximum momentum of accelerated particles, p max , decreases with time, as is the case for the Sedov–Taylor phase of expansion of a shell supernova remnant, when both the shock velocity and the cosmic ray induced magnetization decrease. In this situation, at each time t , particles with momenta larger than p max ( t ) leave the system from upstream, carrying away a large fraction of the energy if the shock is strongly modified by the presence of cosmic rays. This phenomenon is of crucial importance for explaining the cosmic ray spectrum detected at the Earth. In this paper, we discuss how this escape flux appears in the different approaches to non-linear diffusive shock acceleration, and especially in the quasi-stationary semi-analytical kinetic ones. We apply our calculations to the Sedov–Taylor phase of a typical supernova remnant, including in a self-consistent way particle acceleration, magnetic field amplification and the dynamical reaction on the shock structure of both particles and fields. Within this framework, we calculate the temporal evolution of the maximum energy reached by the accelerated particles and of the escape flux towards upstream infinity. The latter quantity is directly related to the cosmic ray spectrum detected at the Earth. 相似文献
15.
宇宙线的观测研究和暗物质粒子的间接探测是高能天体物理领域两个重大研究课题. 自1912年V. Hess发现宇宙线开始, 人类对宇宙线的观测历史已经超过了一个世纪, 传统理论模型预言``膝''区以下能段的宇宙线能谱应服从单一幂率分布, 而近些年的空间和高空气球实验表明10 GeV--100 TeV的宇宙线质子能谱可能存在偏离单一幂律谱分布的重要结构, 这对研究银河系内宇宙线的起源、传播和加速机制具有重要意义. 另一方面, 得益于宇宙线和伽马射线观测精度的提高和观测能段的拓宽, 暗物质粒子的间接探测在国际上受到越来越多的关注, 暗物质粒子可能会发生湮灭或衰变产生稳定的普通高能粒子, 包括正负电子对、正反质子对、伽马射线和中微子等, 进而在宇宙线或伽马射线留下可探测的信号. 相似文献
16.
V. H. Kryvdyk 《Kinematics and Physics of Celestial Bodies》2007,23(2):77-83
We examine the acceleration of cosmic rays in the magnetospheres of collapsing stars with initial dipole magnetic fields and various initial energy distributions of charged particles in their magnetospheres (the exponential, relativistic Maxwellian, and Boltzmann distributions were considered). When a magnetized star contracts at the gravitational collapse stage, its magnetic field grows considerably. Such a variable magnetic field generates an eddy electric field. Our calculations suggest that this electric field can accelerate charged particles to relativistic energies. In this way collapsing stars can be sources of high-energy cosmic rays in our Galaxy as well as in other galaxies. 相似文献
17.
Emmanuel T. Sarris 《Astrophysics and Space Science》1975,36(2):467-472
The intensive acceleration of energetic charged particles in perpendicular shock waves which has been known to take place in the interplanetary medium has been utilized in this work in order to account for the energization of cosmic rays. It is proposed that cosmic rays can be accelerated up to 1014–1015 eV in successive perpendicular shock waves which appear inside supernova shells in our Galaxy. 相似文献
18.
The history of cosmic ray studies can be traced back to the 1910s when Hess and other scientists first discovered them. Cosmic rays are very important laboratories of particle physics, and have led to many important discoveries of fundamental particles, such as the positrons, muons, pions, and a series of strange particles. Cosmic rays are nowadays the key probes of the extremely high-energy physics and dark matter particles. A brief review about the history and recent progresses of direct observations of cosmic rays is presented. In recent years, the new space-borne experiments such as PAMELA and AMS-02, as well as a few of balloon-borne experiments, have measured the energy spectra of cosmic rays very precisely, and revealed several new features/anomalies. Remarkable excesses of positron fraction in the total electron plus positron fluxes have been observed, which may be caused by the annihilation/decay of dark matter particles or by astrophysical pulsars. The cosmic ray antiprotons, which are expected to have the same secondary origin as that of positrons, do not show significant excesses compared with the background prediction. This result also constrains the modeling of the positron excesses. In addition, the spectral hardening above several hundred GeV of cosmic ray nuclei has been revealed. These results have important and interesting implications on our understandings of the origin, acceleration, and propagation of cosmic rays. In particular, China has launched the Dark Matter Particle Explorer (DAMPE) to indirectly search for the dark matter and explore the high-energy universe in the TeV window. Most recently, the DAMPE collaborators reported the new measurements of the cosmic ray electron plus positron fluxes up to about 5 TeV with a very high precision. The DAMPE data revealed clearly a deflection around 0.9 TeV in the electron energy spectrum. Possible fine structures of the electron plus positron spectra can be critically addressed with the accumulation of data in the coming years. 相似文献
19.
T. N. Rengarajan 《Astrophysics and Space Science》1975,32(1):55-75
The capabilities and limitations of pulsars as sources of cosmic rays are reviewed in the light of experimental observations. Pulsars can supply the cosmic ray power if they have rotational velocities in excess of 700 rad s?1 at birth. Though this is theoretically possible, there is no experimental proof for the same. Pulsars can accelerate particles to the highest energies of 1020 eV, but in general, the spectra on simple considerations, turn out to be flatter than the observed cosmic ray spectrum. At the highest energies, absorption processes due to fragmentation and photodisintegration dominate for heavy nuclei. The existence of a steady flux of cosmic rays of energy greater than 1017 eV demands acceleration of particles to last over fifty years, the time interval between supernovae outbursts, whereas the expected period of activity is less than a few years. Finally, the problem of anisotropy with relevance to pulsars as sources and the possibility of observing pulsar accelerated particles from galactic clusters is considered. 相似文献
20.
Our numerical simulations show that the reconnection of magnetic field becomes fast in the presence of weak turbulence in the way consistent with the Lazarian and Vishniac (1999) model of fast reconnection. We trace particles within our numerical simulations and show that the particles can be efficiently accelerated via the first order Fermi acceleration. We discuss the acceleration arising from reconnection as a possible origin of the anomalous cosmic rays measured by Voyagers. 相似文献