共查询到20条相似文献，搜索用时 46 毫秒
1.
Dynamical evolution of a relativistic explosion resulting from a large amount of energy release in a homogenous medium is studied using the Khalatnikov equation describing relativistic, hydrodynamic, planar flow. The early phase of the explosion is idealized to two stages: a free expansion and a shock wave stage. By the hodograph transformation inverting the dependent and independent variables, the hydrodynamic equations for the relativistic flow are reduced to second-order linear equations in a velocity-enthalpy space and they are solved by the method of Laplace transformation. The propagation laws and flow structures of the relativistic expansion are obtained at each stage. In the free expansion stage, the flow with a sufficiently high sound velocity forms a thin shell of the energy density in the comoving frame at the front and accelerates the front. In the shock wave stage, the Lorentz factor of the shock front decreases logarithmically with time. The transition time from a free expansion to a shock wave stage suggests that the super-light expansion observed in extragalactic radio sources has no spherical geometry but must be confined to a narrow cone. 相似文献
2.
Similarity solutions, for one-dimensional unsteady flow of a perfect gas behind a spherical shock wave produced on account of a sudden explosion or driven out by an expanding piston including the effects of radiative cooling, are investigated. The shock ahead of the point of explosion or piston is propagating into a transparent medium at rest with non-uniform density. The total energy of the wave is assumed to be time dependent obeying a power law. 相似文献
3.
J. B. Singh 《Astrophysics and Space Science》1983,96(2):239-244
Similarity solutions for a point explosion in a non-ideal gas, are investigated in the presence of magnetic field. The shock ahead of the point explosion is assumed to be strong. The energy of the expanding wave has been assumed to be time-dependent obeying a power law. The equation of state in the suitable form for such gases is found to be fairly accurate at low density region. 相似文献
4.
J. B. Singh 《Astrophysics and Space Science》1983,96(1):153-158
Similarity solutions, for one-dimensional unsteady of a perfect gas behind a spherical shock wave produced on account of a sudden explosion or driven out by an expanding piston including the effects of radiative cooling and an idealised azimuthal magnetic field, are studied. The shock is assumed to be strong and it is propagating into a transparent medium at rest with varying density. The magnetic field is proportional tor ?1. The total energy of the wave is time dependent obeying a power law. 相似文献
5.
M. Yokosawa 《Astrophysics and Space Science》1982,83(1-2):335-366
Dynamical evolution of a relativistic beam ejected from a galactic centre is studied using the similarity method for the relativistic winds flowing through channels. The expansion phase is divided into two stages: A relativistic expansion and a non-relativistic expansion stage. By the dimensional analysis for a relativistic wind, the propagation law of the expanding wave front is obtained. When the front moves relativistically, the density of the ambient matter observed in the co-moving frame of the front increases by the Lorentz contraction and mass increment, and the propagation law obtained in the classical theory is modified by these relativistic effects. On the basis of a perturbation method, a new similarity method for a relativistic flow whose front velocity is varing with the expansion is presented. The flow structures of the relativistic wind are given. With the expansion of a beam, the inward-facing shock wave is more separated from the front of the outward-expanding shock wave and its shock strength becomes stronger than that of the outward-expanding shock wave when the ejected beam consists of energetic particles. The evolutions of the extragalactic double sources are considered. The relative position of the hot spot in the radio map is presented at each stage of the expansion and discussed with the observational radio maps. The time variation of the radio emission is predicted. 相似文献
6.
A. S. Zentsova 《Astrophysics and Space Science》1983,95(2):459-462
A hypothesis is being put forward that the formation of jets in the nuclei of radio galaxies is due to a high-speed energy excretion (explosion) in the accretion disk around a massive black hole. The explosion can be induced, for example, by a fall of the star into the black hole. For the accretion disk featuring an exponential high-density distribution, an asymmetrical explosion can be obtained: the shock front moves in the direction of decreasing the density accelerately and achieves the relativistic velocity swiftly, carrying away the most fraction of the explosion energy. Radio emission of the jet involves synchrotron radiation of relativistic electrons which are accelerated by such shock wave in the magnetic field driven up by the shock front. 相似文献
7.
The problem of explosion along a line in a gas cloud in the presence of transverse magnetic field has been considered. Similarity solutions of the adiabatic motion of a gas behind an infinitely strong cylindrical shock wave propagating into an infinitely conducting medium at rest is obtained. Shock radius varies exponentially with time and density is inversely proportional to fourth power of shock radius just ahead of the shock front. 相似文献
8.
In the present paper, we have obtained some exact analytic self-similar solutions for a zero-temperature gradient behind a magnetogasdynamic shock wave produced by stellar explosions. The initial density of the medium is taken to vary as some power of the distance from the point of explosion. The solutions are obtained for the cases when the energy of the shocked gas is constant, the energy is varying, and the shock velocity is constant. General solutions are also obtained. We have also analytically obtained the position of the singular surface behind the shock wave. 相似文献
9.
We consider the self-similar problem of a supernova explosion in a radially inhomogeneous medium by taking into account the generation of accelerated relativistic particles. The initial density of the medium is assumed to decrease with distance from the explosion center as a power law, ρ 0 = A/r θ. We use a two-fluid approach in which the total pressure in the medium is the sum of the circumstellar gas pressure and the relativistic particle pressure. The relativistic particle pressure at the shock front is specified as an external parameter. This approach is applicable in the case where the diffusion coefficient of accelerated particles is small and the thickness of the shock front is much smaller than its radius. We have numerically solved a system of ordinary differential equations for the dimensionless quantities that describe the velocity and density behind the shock front as well as the nonrelativistic gas and relativistic particle pressures for various parameters of the inhomogeneity of the medium and various compression ratios of the medium at the shock front. We have established that the shock acceleration of cosmic rays affects most strongly the formation of a supernova shell (making it thinner) in a homogeneous circumstellar medium. A decrease in the circumstellar matter density with distance from the explosion center causes the effect of shock-accelerated relativistic particles on the supernova shell formation to weaken considerably. Inhomogeneity of the medium makes the shell thicker and less dense, while an increase in the compression ratio of the medium at the shock front causes the shell to become thinner and denser. As the relativistic particle density increases, the effect of circumstellar matter inhomogeneity on the shell formation becomes weaker. 相似文献
10.
I. N. Toptygin 《Astronomy Letters》2000,26(6):356-361
A self-similar solution to Sedov’s problem of a strong explosion in a homogeneous medium is generalized to the case of relativistic-particle generation in a supernova remnant; the particles are accelerated by Fermi’s mechanism at the shock front and in the perturbed post-shock region. Self-similarity takes place if the thickness of the prefront is small compared to its radius and if the pressure ratio of the relativistic and nonrelativistic components at the shock front is kept constant. In the presence of relativistic particles, the time dependence of the shock-front radius remains the same as that in their absence, but the plasma parameters in the inner perturbed region change appreciably. The shell of the matter raked up by the explosion is denser and thinner than that in the nonrelativistic case, the relativistic-particle pressure in the central region remains finite, and the nonrelativistic-gas pressure at the explosion center approaches zero. The influence of relativistic particles on the transition to the radiative phase of expansion of the supernova remnant and on its dynamics is studied. It is shown that relativistic particles can decrease several-fold the remnant radius at which the transition to the radiative phase occurs. 相似文献
11.
We show that the excellent optical and gamma-ray data available for GRB 080319B rule out the internal shock model for the prompt emission. The data instead point to a model in which the observed radiation was produced close to the deceleration radius (∼1017 cm) by a turbulent source with random Lorentz factors of ∼10 in the comoving frame. The optical radiation was produced by synchrotron emission from relativistic electrons, and the gamma-rays by inverse-Compton scattering of the synchrotron photons. The gamma-ray emission originated both in eddies and in an inter-eddy medium, whereas the optical radiation was mostly from the latter. Therefore, the gamma-ray emission was highly variable whereas the optical was much less variable. The model explains all the observed features in the prompt optical and gamma-ray data of GRB 080319B. We are unable to determine with confidence whether the energy of the explosion was carried outwards primarily by particles (kinetic energy) or magnetic fields. Consequently, we cannot tell whether the turbulent medium was located in the reverse shock (we can rule out the forward shock) or in a Poynting-dominated jet. 相似文献
12.
In this paper we obtain similarity solutions for the propagation of plane relativistic shock waves in the presence of a transverse magnetic field for the medium, where the nucleon number density obeys a power law of distance from the plane of explosion. The shock surface moves with constant velocity and the total energy of the disturbance is dependent on time. The solutions are applicable only to an isothermal medium or a cold gas. 相似文献
13.
J. B. Singh 《Astrophysics and Space Science》1983,93(1):15-23
In this paper self-similar solutions have been investigated for the propagation of axisymmetric radiative gasdynamic shocks caused by an explosion into an inhomogeneous ideal gas permeated by a current free azimuthal magnetic field. The effects of radiation flux and magnetic field together have been seen in the region of interest on the other flow variables. The total energy of the flow between the inner expanding surface and the shock is taken to be dependent on shock radius obeying a power law. The radiative pressure and energy have been neglected. 相似文献
14.
We further investigate the two-dimensional hydrodynamic explosion model for rapidly rotating and collapsing supernovae (Aksenov et al. 1997), in which the initial energy release inside a fragmenting low-mass neutron star of critical mass ≈0.1M ⊙ moving in a circular orbit at a velocity of ≈18000 km s?1 is reduced considerably. This velocity closely corresponds to a pulsar escape velocity of ≈1000 km s?1 (at a total mass of ≈1.9M ⊙ for the binary of neutron stars). Compared to our previous study (Zabrodina and Imshennik 1999), this energy release was reduced by more than a half. Otherwise, the model in question does not differ from the explosion model with a self-consistent chemical composition of nuclides investigated in the above paper. In particular, the initial energy release was carefully reconciled with a chemical composition. Our numerical solution shows that the reduction in energy release due to the time scales of β processes and neutrino energy losses being finite does not alter the qualitative results of our previous studies (Aksenov et al. 1997; Imshennik and Zabrodina 1999). An intense undamped diverging shock wave (with a total post-shock energy ? 1051 erg at a front radius of ≈10 000 km) is formed; a large asymmetry of explosion with a narrow cone (with a solid angle of ≈π/4) around the leading direction, which coincides with the velocity direction of the low-mass neutron star at the instant of its explosive fragmentation in the two-dimensional model, emerges. A jet of synthesized radioactive nickel, whose mass is estimated by using simple threshold criteria to be M Ni≈(0.02?0.03)M ⊙ is concentrated inside this cone. This appears to be the integrated parameter that is most sensitive to the specified reduction in initial energy release; it is also reduced by almost a half compared to our previous estimate (Imshennik and Zabrodina 1999). The time of propagation of the shock wave inferred in our model to the presupernova surface was estimated for SN 1987A to be 0.5–1.0 h, in agreement with observations. 相似文献
15.
The acceleration of relativistic particles is considered during their intersection with hydromagnetic shock fronts in the presence of randomly distributed large-scale magnetic fields. In a series of astronomical objects, the Larmor radius of the relativistic particles exceeds the width of the shock front. In this case there is a change in the adiabatic invariant which results in an increase in the energy of the particle when it crosses the front in any direction. We have proved that the adiabatic part of the energy change will be partially or completely compensated by its reverse change in the weaker regions of the magnetic field. The acceleration mechanism considered is found to be more effective than the Fermi mechanism.If the mean free path of the particles is much less than the distance between the shock fronts, magnetic small-scale fluctuations cause further scattering of the particles. In this case the particles following and crossing the front will return to it. After reversed crossing, a fraction of the particles-defined by the ratio of the front speed to the particle velocity or of the distance between the fronts to the free path — will not return to the front. It is proved that for both large and small free paths the rates at which the particle gains energy are nearly the same. 相似文献
16.
The propagation of magnetogasdynamic cylindrical shock waves in an exponentially increasing medium including the effects of the azimuthal magnetic field, is investigated. The shock wave moves with variable velocity and the total energy of the wave is variable. It is shown that the magnetic field has its significant effect on the pressure flow velocity and the inner expanding vacuum region. 相似文献
17.
Based on the model of interaction between spherically symmetric expanding matter and the external medium, we have estimated
the parameters of the matter heated by the shock that was produced in the envelope ejected by the explosion of a classical
nova during its interaction with the stellar wind from the optical companion. Using this model, we have shown that the matter
ejected during the outburst in the system CI Camelopardalis had no steep velocity gradients and that the reverse shock could
heat the ejected matter only to a temperature of ∼0.1 keV. Therefore, this matter did not contribute to the mean temperature
and luminosity of the system observed in the energy range 3–20 keV. 相似文献
18.
Shock compression experiments on Kinosaki basalt were carried out in the interest of studying collisional phenomena in the solar nebula. Shock waves of 7 and 31 GPa were generated using a thin flyer plate, and a shock wave of 16 GPa was generated using a thick cylindrical projectile. By employing in-material manganin and carbon pressure gauges, the shock wave attenuation was examined and the propagation velocities of the shock wave and rarefaction wave were measured.The attenuation mechanism consists of two effects: the rarefaction wave and geometrical expansion. The rarefaction effect includes the reflected wave and the edge wave. The efficiency of these mechanisms depends on the geometry of the projectile, initially induced pressure, and materials of the target and projectile.As a result of the experiments, a cylindrical impactor created an isobaric region of size almost equal to the projectile radius. The shock wave in the far field was attenuated similarly with the power of −1.7 to −1.8 of the propagation distance under our experimental conditions. The shock wave generated using a thin flyer plate was attenuated by the rarefaction wave generated on the back surface of the flyer plate and by geometrical expansion effects. The shock wave generated using a thick projectile was attenuated by edge-wave and by geometrical expansion effects.According to elastic theory, the rigidity of basalt at 7 and 31 GPa was calculated as 35±7 and 0±3 GPa, respectively, using the measured rarefaction wave velocities. The decayed shock pressure was related to the ejection velocity of the impact fragments, which were obtained in previous disruption experiments. The attenuation rates in previous experiments were consistent with ours. The previous impact scaling parameter called “nondimensional impact stress (PI)” has been improved. 相似文献
19.
Similarity solutions describing the flow of a perfect gas behind a spherical and cylindrical shock wave in a magnetic field with radiation heat flux have been investigated. The total energy of the expanding wave has been assumed to remain constant. The solutions, however, are only applicable to a gaseous medium where the undisturbed pressure falls as the inverse square of the distance from the line of explosion. 相似文献
20.
《Astroparticle Physics》2011,34(5-6):335-340
We revisit the radar echo technique as an approach to detect ultra-high energy cosmic rays (UHECR). The UHECR extensive air showers generate disk-like ionization fronts propagating with a relativistic velocity and creating fast decaying plasma. We study the reflection of a radio wave, such as the one from a radar transmitter or commercial radio and TV station, from the relativistic ionization front. The reflected wave will be frequency upshifted due to the relativistic Doppler effect and propagate almost normally to the front due to relativistic aberration. The amplitude of the reflected wave depends strongly on the front velocity and parameters (density, collision frequency) of the plasma behind the front. We develop a theory that allows one to find the reflected wave. Using this theory and typical parameters of extensive air showers, we discuss the feasibility of UHECR detection. 相似文献