Solar Impulsive Hard X-Ray Emission and Two-Stage Electron Acceleration

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.     

类星体的有磁厚吸积盘模型

本文讨论了具有磁场的几何厚吸积盘结构和辐射。结果表明:磁场的存在明显地影响吸积盘的总光度和形状。这种模型可以解释类星体的辐射幂谱分布和高度偏振现象。它是类星体主要辐射区域的一种合理模型。     

Characteristics of the radiation emerging from the top of a rayleigh atmosphere—I Intensity and polarization

S. Chandrasekhar's solution of the equation of radiative transfer m a medium scattering according to Rayleigh's law has been used for an extensive series of computations of the scattered and diffusely reflected radiation directed outward from the top of a plane stratified model of the atmosphere. The results are discussed in two parts, the first of which deals with the intensity, degree of polarization, plane of polarization and the neutral points of the scattered and diffusely reflected radiation. Part II (see following article) will be a discussion of the upward flux, integrated over the hemisphere, as a function of wavelength of the incident radiation, and of the albedo of the atmospheric model for an energy distribution of the incident light similar to that of the extra-terrestrial solar spectrum. The results are compared with similar quantities for the diffusely scattered radiation from the sunlit sky.     

Pulsars as sources of cosmic rays

The observed characteristics of pulsars have been considered with respect to how they would affect cosmic rays if pulsars are the sources of cosmic radiation. Particular attention was given to the various time properties of suggested acceleration mechanisms. They are divided into three general cases: (a) constant with time, (b) sudden injections at discrete times, (c) slowly varying with time. In each case the possibility of either a monoenergetic or a power law injection spectrum with respect to energy was taken into account.     

The power spectrum of rich clusters of galaxies on large spatial scales

We present an analysis of the redshift-space power spectrum, P ( k ), of rich clusters of galaxies based on an automated cluster catalogue selected from the APM Galaxy Survey. We find that P ( k ) can be approximated by a power law, P ( k )∝ kⁿ , with n ≈−1.6 over the wavenumber range 0.04< k <0.1 h Mpc⁻¹. Over this range of wavenumbers, the APM cluster power spectrum has the same shape as the power spectra measured for optical and IRAS galaxies. This is consistent with a simple linear bias model in which different tracers have the same power spectrum as that of the mass distribution, but shifted in amplitude by a constant biasing factor. On larger scales, the power spectrum of APM clusters flattens and appears to turn over on a scale k ∼0.03 h Mpc⁻¹. We compare the power spectra estimated from simulated APM cluster catalogues with those estimated directly from cubical N -body simulation volumes, and find that the APM cluster survey should give reliable estimates of the true power spectrum at wavenumbers k ≳0.02 h Mpc⁻¹. These results suggest that the observed turnover in the power spectrum may be a real feature of the cluster distribution, and that we have detected the transition to a near-scale-invariant power spectrum implied by observations of anisotropies in the cosmic microwave background radiation. The scale of the turnover in the cluster power spectrum is in good agreement with the scale of the turnover observed in the power spectrum of APM galaxies.     

A primordial feature at the scale of superclusters of galaxies

We investigate a spatially flat cold dark matter model (with the matter density parameter     with a primordial feature in the initial power spectrum. We assume that there is a bump in the power spectrum of density fluctuations at wavelengths     , which corresponds to the scale of superclusters of galaxies . There are indications for such a feature in the power spectra derived from redshift surveys and also in the power spectra derived from peculiar velocities of galaxies. We study the mass function of clusters of galaxies, the power spectrum of the cosmic microwave background (CMB) temperature fluctuations, the rms bulk velocity and the rms peculiar velocity of clusters of galaxies. The baryon density is assumed to be consistent with the big bang nucleosynthesis value. We show that with an appropriately chosen feature in the power spectrum of density fluctuations at the scale of superclusters, the mass function of clusters, the CMB power spectrum, the rms bulk velocity and the rms peculiar velocity of clusters are in good agreement with the observed data.     

Estimating statistics of sky brightness using radio interferometric observations

Radio interferometers are used to construct high resolution images of the sky at radio frequencies and are the key instruments for accessing the statistical properties of the evolution of neutral hydrogen over cosmic time. Here we use simulated observations of the model sky to assess the efficacy of different estimators of the large-scale structure and power spectrum of the sky brightness distribution. We find that while the large-scale distribution can be reasonably estimated using the reconstructed image from interferometric data, estimates of the power spectrum of the intensity fluctuations calculated from the image are generally biased. This bias is found to be more pronounced for diffuse emission. The visibility based power spectrum estimator, however, gives an unbiased estimate of the true power spectrum. This work demonstrates that for an observation with diffuse emission the reconstructed image can be used to estimate the large-scale distribution of the intensity, while to estimate the power spectrum, visibility based methods should be preferred.With the upcoming experiments aimed at measuring the evolution of the power spectrum of the neutral hydrogen distribution, this is a very important result.     

The radiation field in a semi-infinite atmosphere containing energy sources

The problem of determining the radiation field, in a medium in which the energy sources are distributed in depth according to the power law, under broad assumptions concerning the elementary scattering process, has been reduced to a solution of similar problem in an isothermal atmosphere. In addition, the radiation intensity at a specified point in an isothermal atmosphere is related with that in an atmosphere, illuminated by continuum isotropic radiation. This fact, in particular, enables one to express the intensity of the outgoing radiation for an arbitrary distribution of the internal energy sources in terms of Ambartsumian's -function, or in terms of -functions obtained in more complicated situations, characterized by anisotropic scattering, the general case of frequency redistribution etc. For illustration, the classical Milne-Eddington problem of spectral-line formation is considered.     

Broadband spectrum of the X-ray nova SWIFT J174510.8-262411 at the decaying phase of its outburst

Results of quasi-simultaneous SWIFT and RTT-150 observations for the X-ray nova SWIFT J174510.8-262411 in May–June 2013 at the decaying phase of its outburst are presented. It is shown that the nova spectrum can be fitted in a very wide energy range (from the infrared z and i bands to hard X-rays) by a single power law attenuated due to absorption but without any traces of the presence of a soft (blackbody) component. The presence of such a component is suggested by the generally accepted models of disk accretion onto a black hole in a binary system. The observation of a single power-law spectrum may imply that synchrotron radiation from the source’s relativistic jets makes a major contribution to its flux or that the accretion disk is everywhere hot, optically thin, and radiates nonthermally.     

Cold dark matter models with a step-like initial power spectrum

We investigate the properties of clusters of galaxies in the ΛCDM models with a step-like initial power spectrum. We examine the mass function, the peculiar velocities and the power spectrum of clusters in models with different values of the density parameter Ω₀, the normalized Hubble constant h and the spectral parameter p that describes the shape of the initial power spectrum. The results are compared with observations. We also investigate the rms bulk velocity in the models, where the properties of clusters are consistent with the observed data. We find that the power spectrum of clusters is in good agreement with the observed power spectrum of the Abell–ACO clusters if the spectral parameter p is in the range p =0.6–0.8. The power spectrum and the rms peculiar velocity of clusters are consistent with observations only if Ω₀<0.4 . The models with Ω₀=0.3 are consistent with the observed properties of clusters if h =0.50–0.63. For h =0.65, we find that Ω₀=0.20–0.27.     

On the radiative and thermodynamic properties of the cosmic radiations using COBE FIRAS instrument data: II. Extragalactic far infrared background radiation

Using formula to describe the average spectrum of the extragalactic far infrared background (FIRB) radiation measured by the COBE FIRAS instrument in the 0.15–2.4 THz frequency interval at mean temperature T=18.5 K, the radiative and thermodynamic properties, such as the total emissivity, total radiation power per unit area, total energy density, number density of photons, Helmholtz free energy density, entropy density, heat capacity at constant volume, and pressure are calculated. The value for the total intensity received in the 0.15–2.4 THz frequency interval is equal to 13.6 nW?m^?2?sr^?1. This value is about 19.4 % of the total intensity expected from the energy released by stellar nucleosynthesis over cosmic history. The radiative and thermodynamic functions of the extragalactic far infrared background (FIRB) radiation are calculated at redshift z=1.5.     

The fluctuation origin of cosmic radiation

We have investigated the origin of cosmic radiation in terms of a sudden injection of particles in time, momentum and space. The appropriate boundary conditions for the various regions through which the particles pass were used. With all of the acceleration within a turbulent region, we find that the observed spectrum is explained by a continuous deceleration in which statistical fluctuations dominate. This is contradictory to the usual assumptions in which fluctuations do not play an important part. We find that the time dependent solution has an exponent of the power law spectrum that varies weakly with the momentum and time. The steady state solution shows the usual constant exponent.This work was supported by the National Aeronautics and Space Administration under Grant NsG-695.     

Studies of granular velocities

Spectral observations of solar velocity fields made during a partial solar eclipse are described. Continuum intensity measurements at the lunar limb allow the modulation transfer function to be derived and the true spatial power spectrum of the velocity field to be reconstructed. The oscillatory and granular components are separated by applying spatial filters cutting off at 3.7. The oscillatory component values are in good agreement with those of Canfield (1976) but the granular component has substantially more power and a smaller height gradient. The discrepancy can be resolved by noting the uncertainties of the seeing corrections and of the separation into components in the work of Canfield.However on the basis of this limited material, we would go no further than to claim that the height dependence of the granular velocities remains an open question.Mitteilung aus dem Fraunhofer-Institut Nr. 157.     

活动星系核的多波段能谱及其发射机制──Ⅱ．红外连续辐射能谱

本文讨论了１６个红外强ＰＧ类星体的红外辐射能谱。我们假设这些活动星系核的红外谱是由非热辐射机制和尘埃的热辐射共同产生的，通过对红外包的最佳拟合，我们发现大多数ＰＧ类星体的红外包位于７一２４μ的中远红外区，尘埃的热辐射机制能很好地产生观测到的红外包。通过模拟能定量地说明尘埃产生的热致辐射在这些天体的红外谱中的相对重要性，在模型与观测值之间的拟合中，我们得到了在这些天体中核加热的尘埃区的大小、尘埃的分布等模型参数。     

Terrestrial black holes as sources of super-high energy radiation

Small black holes which can be located in the Earth interior are proposed as sources of superhigh energy radiation and their origin is not constrained to the Big Bang. We estimate the intensity and spectrum of massless and massive particles radiation due to the Hawking effect for black holes with masses of 10⁸-10¹⁶ g and consider possibility of their registration according to the following peculiarities: high particle energies, thermal energetic spectrum, transientness or an explicit trend to the intensity and energy increase, and some expressed direction of emission connected with the source localization.     

A two-component model of impulsive microwave burst emission consistent with soft and hard X-rays

A two-component (core-halo) emission model has been applied reconciling hard and soft X-ray burst emissions with the microwave burst radiation. The core region is represented by a nonthermal energy distribution (Maxwellian+power law tail) and assumed to be surrounded by a thermal halo. Parameters characterizing the energy distribution and emission measures have been derived numerically from soft and hard X-ray measurements. Using an artificial magnetic field model the microwave flux spectrum has been calculated on the basis of gyro-synchrotron emission and absorption by solving the equation of radiation transfer along the ray trajectories. Open parameters were used to adapt the spectrum to the radio measurements.Thus probable informations about the most appropriate magnetic field parameters as well as about the time- and frequency- dependent source diameters (yielding growth velocities of the core region during the impulsive phase) are deduced for the burst of 1972 May 18 as an example. A fit of the observed spectrum at the burst maximum is consistent with a magnetic field of 150O G at the core centre decreasing up to about 40 G at the top of the halo at a height of 50 000 km above the centre, a core density of 10¹⁰ cm^–3 decreasing to 10⁹ cm^–3 at the outer halo boundary, and a core diameter of 15 000 km (]20).Due to the simple geometry and emission process adopted,- the model refers primarily to special impulsive bursts. For the representation of broad band microwave bursts, e.g. type IV , events, a more complex source geometry and/or other variants of the emission mechanism must be invoked.     

Resonant Transition Radiation and Solar Radio Bursts

This paper presents general relations for the intensity of the resonant transition radiation (RTR) and their detailed analysis. This analysis shows that the spectrum amplitude of the x-mode at some frequencies for high-energy electrons can grow with the magnetic field increase in some interval from zero value; it can even dominate over that for the o-mode. With further magnetic field increase, the intensity of the RTR x-mode decreases in comparison with the intensity of the o-mode and this decrease is higher for higher velocities of energetic electrons. The polarization of the RTR depends on the velocity of energetic electrons, too. For velocities lower than some velocity limit v<v _i the RTR emission is unpolarized in a broad interval of magnetic field intensities in the radio source. For reasonable values of indices of the power-law distribution functions of energetic electrons, the RTR is broadband in frequencies (df/f≈0.2−0.4). Furthermore, we show various dependencies of the RTR and its spectral characteristics. Assuming the same radio flux of the transition radiation and the gyro-synchrotron one at the Razin frequency, we estimate the limit magnetic field in the radio source of the transition radiation. Then, we analyze possible sources of small-scale inhomogeneities (thermal density fluctuations, Langmuir and ion-sound waves), which are necessary for the transition radiation. Although the small-scale inhomogeneities connected with the Langmuir waves lead to the plasma radiation, which is essentially stronger than RTR, the inhomogeneities of the ion-sound waves are suitable for the RTR without any other radiation. We present the relations describing the RTR for anisotropic distribution functions of fast electrons. We consider the distribution functions of fast electrons in the form of the Legendre polynomials which depend on the pitch-angle. We analyze the influence of the degree of the anisotropy (an increase of the number of terms in the Legendre polynomial) on spectral characteristics of the RTR. A comparison with previous studies is made. As an example of the use of the derived formulas for the RTR, the 24 December 1991 event is studied. It is shown that the observed decimetric burst can be generated by the RTR in the plasma with the density inhomogeneities at the level 〈ΔN ²〉/N ²=2.5⋅10⁻⁵.     

Fourier analysis of the light curves of eclipsing variables. XIXA:

The radiation of a charge rotating in a circle with the constant velocity (in the external magnetic field) in the isotropic plasma with random inhomogeneities of the electron density has been considered. A general expression is obtained for the radiation intensity at thenth harmonic, which is a generalization of the known Shott formula. In the ultra-relativistic case the conditions are clarified under which the inhomogeneity effect on the form of the spectrum of radiation from a particle is essential. An asymptotic formula is derived for the spectral intensity in the region of sufficiently low frequencies. The mechanism of transient radiation in this case is shown to prevail over the synchrotron one.     

星系团内物理过程对宇宙微波背景辐射的影响

观测表明,富星系团内存在着大量的高温热电子.它们将与微波背景光子相互作用.本文考虑了星系团集合使微波背景辐射产生的畸变.我们的理论估计表明,富星系团集合的高温热电子散射背景光子,使背景辐射谱偏离黑体辐射谱.在背景谱的维恩区,畸变小于2.74K黑体峰值强度的1％,这个结果与最近COBE卫星的探测结果是一致的.没有得到Matsumoto所探测到的在700μm附近有相当于黑体谱峰值强度10％的重大畸变.星系作为微引力透镜,对背景辐射的影响不可能探测得到.星系团内热电子的轫致辐射在微波波段更弱.