共查询到20条相似文献，搜索用时 31 毫秒
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利用太阳射电宽带频谱仪(0．7-7．6GHz)于2001年10月19日观测到的复杂太阳射电大爆发，呈现出许多有趣的特征，结合NoRH(Nobeyama Radio Heliograph)的高空间分辨率射电成像观测及TRACE(Transition Region and Coronal Explorer)在远紫外(EUV)波段的高空间分辨率成像观测资料，分析了该爆发的射电频谱特征和微波射电源的演化以及它们与复杂的EUV日冕环系统的关系，该爆发是一个双带大耀斑的射电表征．前一部分以宽带(从厘米到米波)爆发为主，机制是回旋同步辐射，所对应的是环足源的辐射；后一部分以窄带(分米到米波)分米波爆发为主，机制是等离子体辐射和回旋共振辐射的联合，对应的是环顶源的辐射。 相似文献
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E. I. Robson L. L. Leeuw J. A. Stevens & W. S. Holland 《Monthly notices of the Royal Astronomical Society》1998,301(4):935-940
We present millimetre photometry and submillimetre imaging of the central core and two hotspots in the radio lobes of the galaxy Cygnus A. For both hotspots and the central core, the synchrotron spectrum continues smoothly from the radio to a frequency of 677 GHz. The spectral index of the hotspots is constant over our frequency range, with a spectral index of α ≈ −1.0 ( S ν ∝ να ), which is steeper than at lower frequencies and represents the emission from an aged population of electrons. The core is significantly flatter, with α = −0.6 ± 0.1, suggestive of an injected spectrum with no ageing, but some evidence for steepening exists at our highest observing frequency. Although IRAS data suggest the presence of dust in Cygnus A, our 450-μm data show no evidence of cold dust, therefore the dust component must have a temperature lying between 85 and 37 K, corresponding to dust masses of 1.4 × 106 and 1.0 × 108 M⊙ respectively. 相似文献
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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. 相似文献
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A. Stupp† 《Monthly notices of the Royal Astronomical Society》2002,329(3):567-571
We developed a simple model for a flare loop, which was used to fit the emission in the microwave (17 GHz) and millimetre-wave (80 GHz) ranges for the giant flare of 1991 June 4. The simplicity of the model enabled the exploration of a wide range of parameters in a reasonable time. It was possible, using the simple model, to derive from the 17- and 80-GHz data the magnetic field and the number density for every measurement point in the time range we chose to fit. 相似文献
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Yuan-Chuan Zou Yi-Zhong Fan Tsvi Piran 《Monthly notices of the Royal Astronomical Society》2009,396(2):1163-1170
We calculate the high-energy (sub-GeV to TeV) prompt and afterglow emission of GRB 080319B that was distinguished by a naked-eye optical flash and by an unusual strong early X-ray afterglow. There are three possible sources for high-energy emission: the prompt optical and γ-ray photons IC scattered by the accelerated electrons, the prompt photons IC scattered by the early external reverse-forward shock electrons, and the higher band of the synchrotron and the synchrotron self-Compton emission of the external shock. There should have been in total hundreds of high-energy photons detectable for the Large Area Telescope onboard the Fermi satellite, and tens of photons of those with energy >10 GeV. The >10 GeV emission had a duration about twice that of the soft γ-rays. Astro-rivelatore Gamma a Immagini Leggero (AGILE) could have observed these energetic signals if it was not occulted by the Earth at that moment. The physical origins of the high-energy emission detected in GRB 080514B, GRB 080916C and GRB 081024B are also discussed. These observations seem to be consistent with the current high-energy emission models. 相似文献
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活动星系核的高能辐射机制研究对于揭示其结构和演化特征以及中央驱动之迹具有其重要的意义。近十年来，随着活动星系统结构模型研究以及其高能连续谱观测的发展，解释活动星系统高能辐的非热致电子级联模型得以产生、发展和完善起来。 相似文献
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Suprathermal proton bremsstrahlung (SPB) of energetic protons is an important source of high-energy X-ray and gamma-ray photons
in the interstellar medium. We calculate the suprathermal bremsstrahlung radiation power and the associated energy loss rate
of the radiating protons. Also the mean photon energy from the SPB process is derived which can be used to construct a monochromatic
approximation of the radiation power. The SPB power is the starting point for the quantitative modelling of theoretical SPB
radiation spectra in cosmic sources.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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We discuss the afterglow emission from a relativistic jet that is initially in the radiative regime, in which the accelerated electrons are fast-cooling. We note that such a 'semiradiative' jet decelerates faster than an adiabatic jet does. We also take into account the effect of strong inverse-Compton scattering on the cooling frequency in the synchrotron component and therefore on the light-curve decay index. We find that there are two kinds of light-curve break for the jet effect. The first is an 'adiabatic break', if the electrons become slow-cooling before the jet enters a spreading phase, and the second is a 'radiative break', which appears in the contrary case. We then show how a relativistic jet evolves dynamically and derive the overall temporal synchrotron emission in both cases, focusing on the change in the light-curve decay index around the break time. Finally, in view of our results, we rule out two cases for relativistic jets which do not account for the observed light-curve breaks in a few afterglows : (i) an adiabatic jet with strong Compton cooling ( Y >1) and with the cooling frequency ν c locating in the observed energy range; (ii) a radiative jet with a significant fraction of total energy occupied by electrons ( ε e ∼1) . 相似文献
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Gamma-ray burst afterglows: effects of radiative corrections and non-uniformity of the surrounding medium 总被引：2，自引：0，他引：2
The afterglow of a gamma-ray burst (GRB) is commonly thought to be the result of continuous deceleration of a relativistically expanding fireball in the surrounding medium. Assuming that the expansion of the fireball is adiabatic and that the density of the medium is a power-law function of shock radius, i.e. n ext ∝ R − k , we study the effects of the first-order radiative correction and the non-uniformity of the medium on a GRB afterglow analytically. We first derive a new relation among the observed time, the shock radius and the Lorentz factor of the fireball: t ⊕ = R /4(4− k ) γ2 c, and also derive a new relation among the comoving time, the shock radius and the Lorentz factor of the fireball: t co = 2 R /(5− k ) γc. We next study the evolution of the fireball by using the analytic solution of Blandford &38; McKee. The radiation losses may not significantly influence this evolution. We further derive new scaling laws both between the X-ray flux and observed time and between the optical flux and observed time. We use these scaling laws to discuss the afterglows of GRB 970228 and GRB 970616, and find that if the spectral index of the electron distribution is p = 2.5, implied from the spectra of GRBs, the X-ray afterglow of GRB 970616 is well fitted by assuming k = 2. 相似文献
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István Szapudi & E. Gaztañaga 《Monthly notices of the Royal Astronomical Society》1998,300(2):493-496
We present the results of a numerical study of the fluid f, p and the gravitational w modes for increasingly relativistic non-rotating polytropes. The results for f and w modes are in good agreement with previous data for uniform density stars, which supports an understanding of the nature of the gravitational wave modes based on the uniform density data. We show that the p modes can become extremely long-lived for some relativistic stars. This effect is attributed to the change in the perturbed density distribution as the star becomes more compact. 相似文献
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Hui-Rong Ji Qi-Jun Pu Yi-Hua Yan Yu-Ying Liu Zhi-Jun Chen Cheng-Ming Tan Cong-Ling Cheng De-Bang Lao Shu-Ke Li Zhi-Qiang Wang Min-Hong Yu Jian-Nong Liu Li-Kang Zhang Ji-Yong Gao National Astronomical Observatories Chinese Academy of Sciences Beijing Hebei Semiconductor Research Institute Shijiazhuang 《中国天文和天体物理学报》2005,5(4):433-441
An improved Solar Radio Spectrometer working at 1.10-2.06 GHz with much improved spectral and temporal resolution, has been accomplished by the National Astronomical Observatories and Hebei Semiconductor Research Institute, based on an old spectrometer at 1-2 GHz. The new spectrometer has a spectral resolution of 4 MHz and a temporal resolution of 5ms, with an instantaneous detectable range from 0.02 to 10 times of the quiet Sun flux. It can measure both left and right circular polarization with an accuracy of 10% in degree of polarization. Some results of preliminary observations that could not be recorded by the old spectrometer at 1-2 GHz are presented. 相似文献
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The properties of thermal material co-existing with non-thermal emitting plasma and strong magnetic fields in the powerful jets of active galactic nuclei (AGN) are examined. Theoretical and observational constraints on the physical properties of this 'cold' component are determined. While the presence of a thermal component occupying a fraction ∼ 10−8 of the jet volume is possible, it seems unlikely that such a component is capable of contributing significantly to the total jet energy budget, since the thermal reprocessing signatures that should appear in the spectra have not, as yet, been detected. 相似文献
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We have measured the line widths and nonthermal velocities in 12 solar regions using high resolution EUV data taken by Hinode/EIS. We find that there exists a positive correlation between the intensity and nonthermal velocity for the Fe XII emission line as well as some other lines. The correlation coefficients decrease from the disk center to the limb. However, the nonthermal velocities of a particular spectral line do not vary much in different regions, so they are considered isotropic. In particular, we find that for a coronal loop structure, the largest widths and nonthermal velocities occur at the footpoints, where outflows appear. Based on these observational results, we discuss several physical processes responsible for coronal heating. 相似文献
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详细研究了高能电子产生的回旋同步辐射自吸收的特性,并用磁偶极子场的 射电微波源模型计算了它的光学厚度.发现: (1)自吸率Kv随谐波数s的增加迅速地 下降,以致只有低次谐波(s<5)上的自吸收才会对微波爆发谱产生实质性的影响; (2) 自吸率κv随暗波数s下降的陡度还随高能电子的能谱指数δ的增加和其低能截止能量 E0的下降而迅速增加; (3)κv值还随传播角的增大而增加,并在70°至75°范围内达到 极值; (4)假设高能电子数密度为103cm-3,则在2≤s≤5范围内的自吸收的光学厚 度τvself在101-10-2之间变化,这些值约比回旋共振吸收的光学厚度τvgyro小3至4 个数量级.τvself在均匀磁场情况下可能被高估.只有当被加速的高能电子的数密度大于 104cm-3时,自吸收的光学厚度才开始能与回旋共振吸收的光学厚度相比较. 相似文献