Polarization of the Crab Nebula with disordered magnetic components

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.     

Giant radio sources

We present multifrequency Very Large Array (VLA) observations of two giant quasars, 0437−244 and 1025−229, from the Molonglo Complete Sample. These sources have well-defined FR II radio structure, possible one-sided jets, no significant depolarization between 1365 and 4935 MHz and low rotation measure (|RM|<20 rad m⁻²). The giant sources are defined to be those with overall projected size 1 Mpc. We have compiled a sample of about 50 known giant radio sources from the literature, and have compared some of their properties with a complete sample of 3CR radio sources of smaller sizes to investigate the evolution of giant sources, and test their consistency with the unified scheme for radio galaxies and quasars. We find an inverse correlation between the degree of core prominence and total radio luminosity, and show that the giant radio sources have similar core strengths to smaller sources of similar total luminosity. Hence their large sizes are unlikely to be caused by stronger nuclear activity. The degree of collinearity of the giant sources is also similar to that of the sample of smaller sources. The luminosity–size diagram shows that the giant sources are less luminous than our sample of smaller sized 3CR sources, consistent with evolutionary scenarios in which the giants have evolved from the smaller sources, losing energy as they expand to these large dimensions. For the smaller sources, radiative losses resulting from synchrotron radiation are more significant while for the giant sources the equipartition magnetic fields are smaller and inverse Compton loss owing to microwave background radiation is the dominant process. The radio properties of the giant radio galaxies and quasars are consistent with the unified scheme.     

Multifrequency observations of the jets in the radio galaxy NGC 315

We present images of the jets in the nearby radio galaxy NGC 315 made with the Very Large Array at five frequencies between 1.365 and 5 GHz with resolutions between 1.5 and 45 arcsec. Within 15 arcsec of the nucleus, the spectral index of the jets is  α= 0.61  . Further from the nucleus, the spectrum is flatter, with significant transverse structure. Between 15 and 70 arcsec from the nucleus, the spectral index varies from ≈0.55 on-axis to ≈0.44 at the edge. This spectral structure suggests a change of dominant particle acceleration mechanism with distance from the nucleus and the transverse gradient may be associated with shear in the jet velocity field. Further from the nucleus, the spectral index has a constant value of 0.47. We derive the distribution of Faraday rotation over the inner ±400 arcsec of the radio source and show that it has three components: a constant term, a linear gradient (both probably due to our Galaxy) and residual fluctuations at the level of 1–2 rad m⁻². These residual fluctuations are smaller in the brighter (approaching) jet, consistent with the idea that they are produced by magnetic fields in a halo of hot plasma that surrounds the radio source. We model this halo, deriving a core radius of ≈225 arcsec and constraining its central density and magnetic field strength. We also image the apparent magnetic field structure over the first ±200 arcsec from the nucleus.     

1991年6月6日与白光耀斑共生的微波大爆发

本文简要地介绍了发生于２５４５ＭＨｚ和２６４５ＭＨｚ频率上的一次与白光耀斑共生的微波射电大爆发。该爆发有很高的峰值流量，很高的偏振度和很复杂的偏振状态的变化．同时该爆发的第一主峰期间同时观测到色球层白光耀斑连续辐射。本文还简要地讨论了这次射电爆发与色球白光耀斑的时间演化关系及射电爆发在主峰期间偏振状态急剧变化的原因。     

基于双信号源的双偏振雷达接收机故障诊断技巧

与传统天气雷达相比,双偏振天气雷达在硬件组成上改动较大,尤其是在接收机及天线馈线方面.硬件上的改动使得双偏振雷达的诊断方法存在较大不同.本文通过与传统天气雷达在硬件结构和标定通道两方面的对比,分析了S波段双偏振天气雷达与单偏振雷达在故障诊断方面的区别,提出通过"双信号源+动态法"隔离主通道与测试通道和通过"双信号源+太...     

The early Universe with quantum non-conformal fields

Models for the early Universe with the combined influence of scalar fields and vacuum polarization are discussed using phase plane portraints. The results concern the probability of the birth of the Universe, different de Sitter solutions and expressions for scalar perturbations.     

Elemental abundance analyses with DAO spectrograms — XVIII. The double-lined spectroscopic binary 46 Draconis

Equipartition magnetic fields can dramatically affect the polarization of radiation emerging from accretion disc atmospheres in active galactic nuclei. We extend our previous work on this subject by exploring the interaction between Faraday rotation and absorption opacity in local, plane-parallel atmospheres with parameters appropriate for accretion discs. Faraday rotation in pure scattering atmospheres acts to depolarize the radiation field by rotating the polarization planes of photons after last scattering. Absorption opacity in an unmagnetized atmosphere can increase or decrease the polarization compared to the pure scattering case, depending on the thermal source function gradient. Combining both Faraday rotation and absorption opacity, we find the following results. If absorption opacity is much larger than scattering opacity throughout the atmosphere, then Faraday rotation generally has only a small effect on the emerging polarization because of the small electron column density along a photon mean free path. However, if the absorption opacity is not too large and it acts alone to increase the polarization, then the effects of Faraday rotation can be enhanced over those in a pure scattering atmosphere. Finally, while Faraday rotation often depolarizes the radiation field, it can in some cases increase the polarization when the thermal source function does not rise too steeply with optical depth. We confirm the correctness of the analytic calculation by Silant'ev of the high magnetic field limit of the pure scattering atmosphere, which we incorrectly disputed in our previous paper.     

STUDY OF THE POLARIZATION CHARACTERISTICS OF SKYLIGHT OVER BEIJING

One of the significant characteristics of the sky is the polarization of light,which is formedthrough the multi-scattering process of atmospheric molecules,aerosols and earth's surface,andthus contains information on these three factors.It has recently been paid more attentions toretrieve the characteristic parameters of the aerosol and surface of the earth from the skylightpolarization information.Observation of the skylight polarization over Beijing has been conductedwith a multi-wavelength polarimeter developed by LAGEO(Laboratory for Middle Atmosphereand Global Environment Observation),IAP(Institute of Atmospheric Physics)since November1995.With these observation data,both the seasonal variations of the maximum degree ofpolarization of the skylight and the effect of the surface situation are studied in this paper.AMonte Carlo code for the vector radiative transfer calculation is used to simulate and compare withobservation.     

激电测深法在广西融安县泗顶铅锌矿接替资源勘查中的应用

广西泗项铅锌矿属国家危机矿山,做好危机矿山接替资源找矿工作以延长矿山开采年限,对国家和地方有色工业的可持续发展具有重要的社会和经济意义.论文介绍了在广西泗顶铅锌矿用激发极化法进行找矿的用情况.通过激电测深剖面数据采集,以AB/6(AB为供电极距)为深度轴编制了ηs、ps地电断面图及水平截面等值线平面图,圈出了29个激电测深异常和10个平面异常,其中位于泥盆系地层中的有7个,位于寒武系地层中的有15个,跨越泥盆、寒武系地层的有7个.这些异常对在泗顶铅锌矿探找新矿源提供了重要信息.     

红层地区综合应用联合剖面法和激发极化法找水一例

通过联合剖面法和激发极化法的综合应用,在地处湘乡红层盆地的测区内推断出1条相对富水的断层构造带,经水文物探定孔,钻探施工,抽水试验表明水质水量满足要求.本次水文物探,表明在红层地区综合应用联合剖面法和激发极化法找水是一种行之有效的方法.