电子磁矩对同步辐射频谱的修正

本文从偶极子辐射场的Heaviside-Feynman表达式出发, 用经典的电动力学方法推导了考虑内禀磁矩影响后的相对论电子辐射频谱分布的表达式, 并对做匀速圆周运动的极端相对论性电子的同步辐射, 计算了两个偏振方向上的考虑磁矩修正后的辐射谱. 计算结果表明对于特征频率为ω_c的同步辐射, 如果ħω_c≥10 keV, 内禀磁矩对辐射的修正是可观的. 通过同步辐射的内禀磁矩修正, 本文讨论了电子束极化度与辐射场偏振度的依赖关系, 并基于此关系提出一种测量电子束极化度的新方法. 关键词： 同步辐射 电子内禀磁矩 同步辐射偏振度 束流极化度     

等离子体中相对论电子的同步曲率辐射特性研究

根据同步曲率辐射理论推导了在等离子体环境中,不同磁场条件下的相对论性电子的吸收系数和发射系数表达式，计算了电子的发射强度，并且在此基础上研究了同步曲率辐射机制的脉泽效应.研究了两种磁场位型，第一种是强度均匀但弯曲的磁场，第二种是偶极磁场，结果发现了一些偶极磁场下特有的辐射特性.考虑到在天体的环境下电子具有的不同的能谱分布，分别选用了三种典型的能谱分布(幂率分布，高斯分布，热分布)进行了研究，通过计算负吸收和脉泽放大效应在发射强度上的表现后， 发现在某些天体物理环境中，同步曲率辐射在等离子体中的确存在脉泽放大效应.这些研究结果对太阳系中行星外层辐射的研究和宇宙中的射电高亮温度等问题的研究可能提供有益的帮助. 关键词： 同步曲率辐射 负吸收 脉泽效应     

Polarization bremsstrahlung from relativistic electrons moving in a small-grained medium

Polarization bremsstrahlung from relativistic electrons moving in a medium consisting of very small crystals oriented at random is studied theoretically. The results of this analysis predict a sharp dependence of the spectral and angular features of the radiation on the crystal dimensions and on the angle of observation. The possibility of developing, on the basis of the phenomena considered in the present study, a newmet hod for studying lowly ordered media is highlighted.     

Origination of gamma-ray burst pulses associated with the Doppler effect of spherical fireballs or uniform jet

Ryde and Petrosian have pointed out that the rise phases of gamma-ray burst (GRB) pulses originate from the widths of the intrinsic pulses and their decay phases are determined by the curvature effect of the expanding fireball surface based on their simplified formula. In this paper we investigate in detail the issue based on the formula in Ref.[20], which is derived based on a model of highly symmetric expanding fireballs, where the Doppler effect is the key factor to be concerned about, and no terms are omitted in their derivation. Our analyses show that the decay phases of the observed pulses originate from the contributions from both the curvature effect of the expanding fireball and the two timescales of the local pulses, and the rise phases of the observed pulses only come from the two timescales of the local pulses. Associated with a local pulse with both rise and decay portions, the light curve of GRBs in the rise portion is expected to undergo a concave phase and then a convex one, whereas that in the decay portion is expected to evolve by an opposite process. And the ratio of the concave timescale to the convex one in the rise phase of the observed pulse linearly increases with the ratio of the rising timescale to the decay one of the local pulse ($r_{\rm rd}$), whereas the ratio of the convex timescale to the concave timescale in its decay phase linearly decreases with $r_{\rm rd}$. The two correlations are independent of the local pulse forms and the rest-frame radiation forms. But the different forms of local pulses and the different values of $r_{\rm rd}$ gives rise to the diversity of the light curve pulse shapes. We test a sample of 86 GRB pulses detected by the BATSE instrument on board the Compton Gamma Ray Observatory and find that the characteristics do exist in the light curve of GRBs.     

Production of a keV x-ray beam from synchrotron radiation in relativistic laser-plasma interaction

We demonstrate that a beam of x-ray radiation can be generated by simply focusing a single high-intensity laser pulse into a gas jet. A millimeter-scale laser-produced plasma creates, accelerates, and wiggles an ultrashort and relativistic electron bunch. As they propagate in the ion channel produced in the wake of the laser pulse, the accelerated electrons undergo betatron oscillations, generating a femtosecond pulse of synchrotron radiation, which has keV energy and lies within a narrow (50 mrad) cone angle.     

Lienard-Wiechert potentials and synchrotron radiation from a relativistic spinning particle in pseudoclassical theory

For a relativistic spinning particle with an anomalous magnetic moment, Lienard-Wiechert potentials are constructed within the pseudoclassical approach. Some specific cases of the motion of a spinning particle are considered on the basis of general expressions obtained in this study for the Lienard-Wiechert potentials. In particular, the intensity of the synchrotron radiation from a transversely polarized particle moving along a circle at a constant speed is investigated as a function of the particle spin. In the specific case of particles having no anomalous magnetic moment and moving in an external uniform magnetic field, the resulting expressions coincide with familiar formulas from the quantum theory of radiation. The spin dependence of the polarization of synchrotron radiation is investigated.     

Polarization of coherent synchrotron radiation from an electron beam rotating in a plasma

After eliminating reflections from the walls of the plasma container, we observed polarization of the coherent synchrotron radiation from a relativistic electron beam rotating in a plasma. Several features of the polarization agree well with calculations based on the single particle synchrotron radiation theory. A particular polarization ratio (Fig. 3) does not, however. We deduce from this direct diffraction of the radiation by the beam electrons. This is strong evidence for beam-particle bunches of size cm. Also, there must be some absorption of the extraordinary wave to account for the observations. We suggest a way to apply these results to measure the pitch angle of the beam.Work supported by Army Research Office.     

Annihilation luminosity of a neutrino-cooled accretion disk in a gamma-ray burst

We discuss how the annihilation luminosity of a neutrino-cooled accretion disk in a gamma-ray burst, Lν ν, is determined by the disk’s fundamental parameters, namely, the mass of the central black hole M, the mass accretion rate M, and the viscosity parameter α. It is shown that Lν ν depends mainly on M in evidence, and decreases with increasing M, but is almost independent of α. This result argues additionally that the central black hole in a gamma-ray burst must be with a stellar mass.     

Limits on the cosmological abundance of supermassive compact objects from a millilensing search in gamma-ray burst data

A new search for the gravitational lens effects of a significant cosmological density of supermassive compact objects (SCOs) on gamma-ray bursts (GRBs) has yielded a null result. We inspected the timing data of 774 BATSE-triggered GRBs for evidence of millilensing: repeated peaks similar in light-curve shape and spectra. Our null detection leads us to conclude that, in all candidate universes simulated, Omega(SCO)<0.1 is favored for SCO masses in the range 10(5)相似文献   

Measurement of the time structure of a coherent synchrotron radiation burst in NewSUBARU

The time structure of a burst of coherent synchrotron radiation (CSR) emitted from a high-peak-current beam in the electron storage ring NewSUBARU has been investigated. The source of this CSR burst is fine time structure in a bunch produced by longitudinal beam instability. This burst is unstable but very easy to obtain, so it can be used for some experimental applications with appropriate averaging of data. With an averaging period of 10 ms, the fluctuation of the integrated power was about 10%.     

Polarization of vacuum in a hydrogen-like relativistic atom: Hyperfine structure

An analysis is made of the contribution of the polarization of vacuum to the hyperfine splitting of the ground state of a hydrogen-like atom. An expression for the correction to the energy is obtained as an explicit function of the parameter Zα. The final expression derived in terms of generalized hypergeometric functions and their derivatives is a function of the particle mass ratio in orbit and in a vacuum loop, and is therefore valid for both ordinary and muonic atoms. Various asymptotic forms are also given.     

Luminosity-peak energy relation in the decay phases of gamma-ray burst pulses

Using time-resolved spectral data for a sample of 30 pulses in 27 bright GRBs detected with CGRO/BATSE, we investigate the luminosity-peak energy relation (L-E p relation) in the decay phases of these pulses. A tight L-E p relation is found for most of the pulses, but its power law index is various among pulses, which is normally distributed at 1.84±0.60(1σ) for the pulses in our sample, roughly consistent with the L-E p relation within a GRB and the isotropic gamma-ray energy-E p relation among GRBs. The large scatter of the power law index cannot be explained with both the statistical or observational effects and it may be an intrinsic feature, indicating that no universal L-E p relation would be expected among GRBs/pulses. This may strongly weaken the cosmological use of this relation.     

Polarization of the vacuum in a relativistic hydrogenlike atom: The Lamb shift

This paper examines the shift of energy levels in a hydrogenlike atom induced by vacuum polarization effects. The contribution of free polarization is found for the ground state and several excited states in a closed analytical form. For the first time an expression is derived for the radiative correction to the energy in the form of an explicit function of the parameter Zα. The results are valid for states nl _j with the largest values of orbital and total angular momenta (l=n−1 and j=l+1/2). The final expression, found in terms of generalized hypergeometric functions, is a function of three variables, Zα, n, and the ratio of the particle masses on the orbit and in the vacuum loop, i.e., the result is valid for ordinary atoms and for muonic atoms. Several useful asymptotic expressions are also derived. Zh. éksp. Teor. Fiz. 116, 1575–1586 (November 1999)     

Polarization of photons emitted in the process of resonant coherent excitation of relativistic ions under planar channeling conditions

Owing to the recent observation of the strong anisotropy of characteristic X-ray radiation accompanying the resonant coherent excitation of relativistic Fe²⁴⁺ ions under planar channeling conditions in a silicon crystal, the resonant coherent excitation method can be considered as a candidate for a source of polarized X-ray radiation. The Stokes parameters of the radiation have been calculated using the density matrix approach. The behavior of the polarization characteristics of the radiation in various directions has been explained by considering the properties of the resonance part of the crystal field, which excites an ion and has the form of an elliptically polarized electric field.     

Standard radiation spectrum of relativistic electrons: beyond the synchrotron approximation

Radiation emitted by an electron in arbitrary, extreme relativistic motion, has been described for the first time in terms of a standard spectrum of nonsynchrotron type. Ultimately, such a nonsynchrotron spectrum is dependent not only on instantaneous trajectory curvature, but also upon its first two time derivatives and helicity, to provide a basic correction to the synchrotron approximation (SA). A strong deviation from SA has been predicted for above GeV electrons in oriented crystals.