共查询到20条相似文献,搜索用时 31 毫秒
1.
S. V. Bogovalov D. V. Khangulyan A. V. Koldoba G. V. Ustyugova F. A. Aharonian 《Monthly notices of the Royal Astronomical Society》2008,387(1):63-72
In this paper, we present a detailed hydrodynamical study of the properties of the flow produced by the collision of a pulsar wind with the surrounding in a binary system. This work is the first attempt to simulate interaction of the ultrarelativistic flow (pulsar wind) with the non-relativistic stellar wind. Obtained results show that the wind collision could result in the formation of an 'unclosed' (at spatial scales comparable to the binary system size) pulsar wind termination shock even when the stellar wind ram pressure exceeds significantly the pulsar wind kinetic pressure. Moreover, the post-shock flow propagates in a rather narrow region, with very high bulk Lorentz factor (γ∼ 100). This flow acceleration is related to adiabatic losses which are purely hydrodynamical effects. Interestingly, in this particular case, no magnetic field is required for formation of the ultrarelativistic bulk outflow. The obtained results provide a new interpretation for the orbital variability of radio, X-ray and gamma-ray signals detected from binary pulsar system PSR B1259−63/SS2883. 相似文献
2.
Y. E. Lyubarsky 《Monthly notices of the Royal Astronomical Society》2002,329(2):L34-L36
Origin of the jet-like feature in the inner Crab Nebula is discussed. Because self-collimation processes in ultrarelativistic pulsar winds are extremely ineffective, it is suggested that the collimation occurs beyond the termination shock where the flow is already mildly (or non-) relativistic. It is argued that the shock shape is highly non-spherical because the energy flux in the pulsar wind decreases towards the axis. The shock near the axis should be much closer to the pulsar than at the equator and therefore the jet looks as if it originates directly from the pulsar. 相似文献
3.
In this paper, we present an expanding disc model to derive the polarization properties of the Crab nebula. The distribution function of the plasma and the energy density of the magnetic field are prescribed as functions of the distance from the pulsar using the model derived by Kennel and Coroniti with σ= 0.003 , where σ is the ratio of the Poynting flux to the kinetic energy flux in the bulk motion just before the termination shock. Unlike the case for previous models, we introduce a disordered magnetic field, which is parametrized by the fractional energy density of the disordered component. The flow dynamics are not solved, and the mean field is toroidal.
The averaged degree of polarization over the disc is obtained as a function of the inclination angle and fractional energy density of the disordered magnetic field. It is found for the Crab Nebula that the disordered component contains about 60 per cent of the magnetic field energy. This value is supported by the facts that the disc appears not as 'lip-shaped' but as 'rings' in the observed intensity map, and that the highest degree of polarization of ∼40 per cent is reproduced for rings, which is consistent with the observations.
We suggest that, because the disordered field contributes to the pressure rather than to the tension, the pinch force may have been overestimated in previous relativistic magnetohydrodynamic simulations. The disruption of the oppositely directed magnetic fields, which is proposed by Lyuvarsky, may actually take place. The relativistic flow speed, which is indicated by the front–back contrast, can be detected in the asymmetry of distributions of the position angle and depolarization. 相似文献
The averaged degree of polarization over the disc is obtained as a function of the inclination angle and fractional energy density of the disordered magnetic field. It is found for the Crab Nebula that the disordered component contains about 60 per cent of the magnetic field energy. This value is supported by the facts that the disc appears not as 'lip-shaped' but as 'rings' in the observed intensity map, and that the highest degree of polarization of ∼40 per cent is reproduced for rings, which is consistent with the observations.
We suggest that, because the disordered field contributes to the pressure rather than to the tension, the pinch force may have been overestimated in previous relativistic magnetohydrodynamic simulations. The disruption of the oppositely directed magnetic fields, which is proposed by Lyuvarsky, may actually take place. The relativistic flow speed, which is indicated by the front–back contrast, can be detected in the asymmetry of distributions of the position angle and depolarization. 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.
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
6.
The problem of effective transform of Poynting flux energy into the kinetic energy of relativistic plasma outflow in a magnetosphere
is considered. In this article we present an example of such acceleration. In order to perform it, we use the approach of
ideal axisymmetric magnetohydrodynamics (MHD). For highly magnetized plasma outflow we show that a linear growth of Lorentz
factor with a cylindrical distance from the rotational axis is a general result for any field configuration in the sub-magnetosonic
flow. In the far region the full magnetohydrodynamics problem for one-dimensional flow is considered. It turns out that the
effective plasma outflow acceleration is possible in the paraboloidal magnetic field. It is shown that such an acceleration
is due to the drift of charged particles in the crossed electric and magnetic field. The clear explanation of the absence
of acceleration in the monopole magnetic field if given.
相似文献
7.
We interpret the observed X-ray morphology of the central part of the Crab Nebula (torus + jets) in terms of the standard theory by Kennel and Coroniti (1984). The only new element is the inclusion of anisotropy in the energy flux from the pulsar in the theory. In the standard theory of relativistic winds, the Lorentz factor of the particles in front of the shock that terminates the pulsar relativistic wind depends on the polar angle as γ = γ0 + γ m sin2 θ, where γ0∼200 and γm∼4.5×106. The plasma flow in the wind is isotropic. After the passage of the pulsar wind through the shock, the flow becomes subsonic with a roughly constant (over the plerion volume) pressure P=1/3;n∈ where n is the plasma particle density and ∈ is the mean particle energy. Since ∈∼γmc 2, a low-density region filled with the most energetic electrons is formed near the equator. A bright torus of synchrotron radiation develops here. Jet-like regions are formed along the pulsar rotation axis, where the particle density is almost four orders of magnitude higher than that in the equatorial plane, because the particle energy there is four orders of magnitude lower. The energy of these particles is too low to produce detectable synchrotron radiation. However, these quasijets become comparable in brightness to the torus if additional particle acceleration takes place in the plerion. We also present the results of our study of the hydrodynamic interaction between an anisotropic wind and the interstellar medium. We compare the calculated and observed distributions of the volume emissivity of X-ray radiation. 相似文献
8.
Martin A. Lee 《Astrophysics and Space Science》1998,264(1-4):497-508
The interaction of interstellar pickup ions with the solar wind termination shock is reviewed and assessed. The pickup ions
mass and momentum load the wind and increase its pressure, effects which decrease the strength of the shock and its distance
from the Sun. The pickup hydrogen may contribute substantially to the "reflected" ion population, which should provide most
of the dissipation at the supercritical quasi-perpendicular shock. A fraction of the pickup ions impinging on the shock is
"injected" into the process of diffusive shock acceleration to form the anomalous cosmic ray component. An injection mechanism
which accounts for the apparent absence of solar wind ions in the anomalous component is "shock surfing", in which pickup
ions which approach the shock slowly may be trapped between the upstream Lorentz force and the shock potential and accelerated
in the motional electric field beyond the energy threshold for diffusive shock acceleration. However, the simplest interpretation
of shock surfing would favor less massive pickup ion species, in contradiction with Voyager observations of anomalous component
composition. A possible extension of the shock surfing mechanism is considered, as well as other injection mechanisms. Finally,
the pressure of the anomalous component may modify the structure of the termination shock, which in turn may influence injection
rates.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
We study the multi-waveband non-thermal emission from the pulsar wind neb- ulae (PWNe) Vela X and G0.9 + 0.1 in the frame of a time-dependent model describing non-thermal radiation from the PWNe. In such a model, the relativistic wind of parti- cles driven by a central pulsar blows into the ambient medium and creates a termination shock that accelerates the particles to very high energy in a PWN. The non-thermal pho-tons in the PWN are produced both by synchrotron radiation and the inverse Compton process, with electrons coming directly from the pulsar magnetosphere and electrons be- ing accelerated at the termination shock. We apply this model to reproduce the observed multi-waveband photon spectra of Vela X and the G0.9+0.1, both of which have been detected emitting very high energy photons. Our results indicate that TeV photons are produced by the inverse Compton scattering of the high-energy electrons in the infrared photon field in both Vela X and PWN G0.9+0.1. The TeV photons from these two PWNe may have leptonic origins. 相似文献
10.
S.S. Komissarov 《Monthly notices of the Royal Astronomical Society》2001,326(3):L41-L44
The time-dependent general relativistic equations of degenerate electrodynamics are solved numerically in order to study the mechanism of the electromagnetic extraction of the rotational energy of black holes. We performed a series of 2D runs for black holes with specific angular momentum, a , from 0.1 to 0.9 and for a monopole magnetic field assuming axisymmetry. In the inner region of the wind, the solution quickly settles to a steady state with an outgoing Poynting flux. In all cases the angular velocity of the magnetic field lines is almost half the angular velocity of the black hole. Thus, at least for the configuration considered, the Blandford–Znajek mechanism operates near its maximum power output. 相似文献
11.
Shock surfing acceleration 总被引:1,自引:0,他引:1
Analytical and numerical analysis identify shock surfing acceleration as an ideal pre-energization mechanism for the slow pick-up ions at quasiperpendicular shocks. After gaining sufficient energy by shock surfing, pick-up ions undergo diffusive acceleration to reach their observed energies. Energetic ions upstream of the cometary bow shock, acceleration of solar energetic particles by magnetosonic waves in corona, ion enhancement in interplanetary shocks, generation of anomalous cosmic rays from interstellar pick-up ions at the termination shock are some of the cases where shock surfing acceleration apply. Inclusion of the lower-hybrid wave turbulence into the laminar model of shock surfing can explain the preferential acceleration of heavier particles as observed by Voyager at the termination shock. At relativistic energies, unlimited acceleration of ions is theoretically possible; because for sufficiently strong shocks main limitation of the mechanism, caused by the escape of accelerated particles downstream of the shock during acceleration no longer exists. 相似文献
12.
An explanation of the magnetic fields of the universe, the central mass concentration of galaxies, the massive black hole
of every galaxy, and the AGN phenomena has been an elusive goal. We suggest here the outlines of such a theoretical understanding
and point out where the physical understanding is missing. We believe there is an imperative to the sequence of mass flow
and hence energy flow in the collapse of a galactic mass starting from the first non-linearity appearing in structure formation
following decoupling. This first non-linearity of a two to one density fluctuation, the Lyman-α clouds, ultimately leads to
the emission spectra of the phenomenon of AGN, quasars, blazars etc. The over-arching physical principle is the various mechanisms
for the transport of angular momentum. We believe we have now understood the new physics of two of these mechanisms that have
previously been illusive and as a consequence they impose strong constraints on the initial conditions of the mechanisms for
the subsequent emission of the gravitational binding energy. The new phenomena described here are: 1) the Rossby vortex mechanism
of the accretion disk viscosity, and 2) the mechanism of the α - Ω dynamo in the accretion disk. The Rossby vortex mechanism
leads to a prediction of the black hole mass and rate of energy release and the α - Ω dynamo leads to the generation of the
magnetic flux of the galaxy (and the far greater magnetic flux of clusters) and separately explains the primary flux of energy
emission as force-free magnetic energy density. This magnetic flux and magnetic energy density separately are the necessary
consequence of the saturation of a dynamo created by the accretion disk with a gain greater than unity.
The predicted form of the emission of both the flux and the magnetic energy density is a force-free magnetic helix extending
axially from the disk a distance depending upon its winding number and radius of its flux surfaces, a distance of Mpc's. This
Poynting flux of magnetic energy would be invisible unless the currents bounding the magnetic field are dissipated. By definition
of force-free, these currents are parallel to the field and throughout its volume. Therefore the dissipation must be throughout
the volume as opposed to the conventional reconnection which takes place only at surface layers. This radically different
interpretation of reconnection is supported by the observation of "interruption" events in fusion tokamak experiments. Here,
and presumably in the galactic case as well, the parallel currents and their dissipation is mediated by run-away, high energy
electrons and ions. It is then natural to seek an explanation for the emission spectrum of the dynamo-produced Poynting flux
in the same synchrotron emission associated with the dissipation of these run-away currents. We propose the radically different
view that these ultra high energy, run-away electrons directly produce the emission spectra as compared to the published models
that assume an acceleration of bulk matter to a γ ∼ 10 and then reconvert this kinetic energy by shock heating into a highly
relativistic plasma, γ ∼ 106.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
S. V. Bogovalov F. A. Aharonian 《Monthly notices of the Royal Astronomical Society》2000,313(3):504-514
We show that the relativistic wind of the Crab pulsar, which is commonly thought to be invisible in the region upstream of the termination shock at r r S ∼0.1 pc, in fact could be directly observed through its inverse Compton (IC) γ -ray emission. This radiation is caused by illumination of the wind by low-frequency photons emitted by the pulsar, and consists of two, pulsed and unpulsed , components associated with the non-thermal (pulsed) and thermal (unpulsed) low-energy radiation of the pulsar, respectively. These two components of γ -radiation have distinct spectral characteristics, which depend essentially on the site of formation of the kinetic-energy-dominated wind, as well as on the Lorentz factor and the geometry of propagation of the wind. Thus, the search for such specific radiation components in the spectrum of the Crab Nebula can provide unique information about the unshocked pulsar wind that is not accessible at other wavelengths. In particular, we show that the comparison of the calculated flux of the unpulsed IC emission with the measured γ -ray flux of the Crab Nebula excludes the possibility of formation of a kinetic-energy-dominated wind within 5 light-cylinder radii of the pulsar, R w 5 R L . The analysis of the pulsed IC emission, calculated under reasonable assumptions concerning the production site and angular distribution of the optical pulsed radiation, yields even tighter restrictions, namely R w 30 R L . 相似文献
14.
15.
Lepping R.P. Berdichevsky D.B. Burlaga L.F. Lazarus A.J. Kasper J. Desch M.D. Wu C.-C. Reames D.V. Singer H.J. Smith C.W. Ackerson K.L. 《Solar physics》2001,204(1-2):285-303
The energetic charged particle, interplanetary magnetic field, and plasma characteristics of the `Bastille Day' shock and
ejecta/magnetic cloud events at 1 AU occurring over the days 14–16 July 2000 are described. Profiles of MeV (WIND/LEMT) energetic
ions help to organize the overall sequence of events from the solar source to 1 AU. Stressed are analyses of an outstanding
magnetic cloud (MC2) starting late on 15 July and its upstream shock about 4 hours earlier in WIND magnetic field and plasma
data. Also analyzed is a less certain, but likely, magnetic cloud (MC1) occurring early on 15 July; this was separated from
MC2 by its upstream shock and many heliospheric current sheet (HCS) crossings. Other HCS crossings occurred throughout the
3-day period. Overall this dramatic series of interplanetary events caused a large multi-phase magnetic storm with min Dst lower than −300 nT. The very fast solar wind speed (≥ 1100 km s−1) in and around the front of MC2 (for near average densities) was responsible for a very high solar wind ram pressure driving
in the front of the magnetosphere to geocentric distances estimated to be as low as ≈ 5 R
E, much lower than the geosynchronous orbit radius. This was consistent with magnetic field observations from two GOES satellites
which indicated they were in the magnetosheath for extended times. A static force-free field model is used to fit the two
magnetic cloud profiles providing estimates of the clouds' physical and geometrical properties. MC2 was much larger than MC1,
but their axes were nearly antiparallel, and their magnetic fields had the same left-handed helicity. MC2's axis and its upstream
shock normal were very close to being perpendicular to each other, as might be expected if the cloud were driving the shock
at the time of observation. The estimated axial magnetic flux carried by MC2 was 52×1020 Mx, which is about 5 times the typical magnetic flux estimated for other magnetic clouds in the WIND data over its first
4 years and is 17 times the flux of MC1. This large flux is due to both the strong axially-directed field of MC2 (46.8 nT
on the axis) and the large radius (R
0=0.189 AU) of the flux tube. MC2's average speed is consistent with the expected transit time from a halo-CME to which it
is apparently related. 相似文献
16.
A. Balogh 《Planetary and Space Science》1977,25(10):947-955
A forward-reverse interplanetary shock was observed on 25 March 1969 by the magnetometer and plasma detector on the HEOS-1 satellite. This relatively rare event was described by Chao et al (1972) who concluded that the shock pair was formed at a distance 0.10–0.13 A.U. upstream of the Earth as a result of the interaction between a fast and a slow solar wind streams. Simultaneous observations of 1 MeV solar proton fluxes were also performed on HEOS-1. A characteristic intensity peak was observed as the forward shock passed by the spacecraft. The evolution of the proton intensity, together with a detailed analysis of anisotropies and pitch angle distributions show a complex dynamic picture of the effect of the forward shock on the ambient proton population. Significant changes in particle fluxes are seen to be correlated with fluctuations in the magnetic field. It is suggested that simple geometrical models of shock-associated acceleration should be expanded to include the effect of magnetic fluctuations on particle fluxes. The interaction region limited by the forward and reverse shocks contained a large variety of magnetic fluctuations. Following the tangential discontinuity separating the fast solar wind stream from the preceding slow stream, a sunward flow was observed in the proton data, followed by a small but significant drop in intensity prior to the reverse shock. 相似文献
17.
Dmitry Khangulyan Slavomir Hnatic Felix Aharonian 《Astrophysics and Space Science》2007,309(1-4):261-265
The inverse Compton (IC) scattering of ultrarelativistic electrons accelerated at the pulsar wind termination shock is generally
believed to be responsible for TeV gamma-ray signal recently reported from the binary system PSR B1259-63/SS2883. In such
a system the acceleration takes place in the presence of a dense radiation field provided by a companion Be2-type star. Thus
it is natural to expect an orbital phase dependence of the acceleration efficiency in the system. The HESS collaboration reported
the tendency of reduction of TeV γ-rays around the periastron. In this paper we study a possible explanation of this effect by the “early” (sub-TeV) cutoffs
in the energy spectrum of accelerated electrons due to the enhanced rate of Compton losses close to the periastron. 相似文献
18.
19.
Wen-Rui Hu 《Astrophysics and Space Science》1984,98(1):171-189
The influence of the momentum addition, which may be associated with the average or fluctuation transverse component of the magnetic field or others, on the acceleration the solar wind or stellar wind is studied in a local streamtube. The results show that the larger the momentum addition the stronger the acceleration of the wind. For example, if the typical transverse magnetic field is about 0.1 of the longitudinal field, the velocity of the solar wind at 1 AU may be increased by 40%. The coronal hole may be considered as a streamtube, the presence of a high stream from the coronal hole may be explained by the existence of an average or fluctuation transverse magnetic field in the streamtube. A similar conclusion may be applied to the polar region, where the velocity of the solar wind will be larger than elsewhere as if there is a transverse component of magnetic field, as well as to the stellar wind. The influence of other parameters on the acceleration of the solar wind is also discussed. From the viewpoint of the solar wind mechanism, the present paper shows that the momentum addition in the subsonic flow region can increase the velocity of the solar wind at 1 AU. 相似文献
20.
A. Sierpowska-Bartosik W. Bednarek 《Monthly notices of the Royal Astronomical Society》2008,385(4):2279-2288
At least one massive binary system containing an energetic pulsar, PSR B1259−63/SS2883, has been recently detected in the TeV γ-rays by the HESS telescopes. These γ-rays are likely produced by particles accelerated in the vicinity of the pulsar and/or at the pulsar wind shock, in comptonization of soft radiation from the massive star. However, the process of γ-ray production in such systems can be quite complicated due to the anisotropy of the radiation field, complex structure of the pulsar wind termination shock and possible absorption of produced γ-rays which might initiate leptonic cascades. In this paper, we consider in detail all these effects. We calculate the γ-ray light curves and spectra for different geometries of the binary system PSR B1259−63/SS2883 and compare them with the TeV γ-ray observations. We conclude that the leptonic inverse-Compton model, which takes into account the complex structure of the pulsar wind shock due to the aspherical wind of the massive star, can explain the details of the observed γ-ray light curve. 相似文献