排序方式： 共有12条查询结果，搜索用时 15 毫秒
1.
R. K. Manchanda 《Journal of Astrophysics and Astronomy》2001,22(2-3):145-154
Spectral measurement of Mkn 421 were made in the hard X-ray energy band of 20–200 keV using a high sensitivity, large area
scintillation counter telescope on November 21, 2000 and these coincided with the onset of an active X-ray phase as seen in
the ASM counting rates on board RXTE. The observed spectrum can not be fitted to a single power law similar to the PDS data
of BeppoSAX. The data can be fitted both by a two component power-law function or a combination of an exponential function
with a power law component at the high energies above 80 keV. We identify these components with those arising from the synchrotron
self compton and the high energy power-law tail arising from the upgrading of the thermal photons due to multiple Compton
scattering a la Cyg X-1. A comparison with the earlier data clearly suggests a spectral variability in the hard X-ray spectrum
of the source. We propose a continuously flaring geometry for the source as the underlying mechanism for energy release. 相似文献
2.
本文对视超光速源样本的有关数据进行统计分析，检验活动星系核统一模式。给出各类视超光速源的Ｒ（核光度与扩展区光度之比）分布和喷流与视线的平均夹角 。分析源样本的Ｒ、洛伦兹因子ｒ、喷流的投影尺度ｄ和线性尺度ｌ间的关系，发现Ｒ和ｄ之间存在反相关、ｒ和ｌ之间存在相关的特性，这些结果有利于说明活动星系核统一模式的取向效应。 相似文献
3.
We present the preliminary results for a sample of 21 high luminosity ULIRGs (LIR > 1012.3 L⊙), selected from the 1Jy sample. Based on R band imaging we have performed an analysis of their morphologies. The main
result obtained is that about half of the host galaxies are represented by spheroids and in the other half an exponential
disk has been detected or they show still trace of a merging process going on. Regarding the relation between morphology and
nuclear activity it seems that more advanced mergers appear in the most active galaxies. Hence the data support the evolutionary
scheme proposed by Sanders 15 years ago that ULIRGs can be the earliest precursors of optical QSOs.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
Alfonso Cavaliere 《Astrophysics and Space Science》2004,294(1-2):109-124
I review the processes that govern the amount and the thermal state of the hot plasma pervading clusters and groups of galaxies:
the gravitational heating driven by the DM merging histories, the radiative cooling of baryons, and the energy fed back by
SNe and by AGNs or quasars. I argue that the X-ray emissions and the entropy levels now observed from clusters to groups require
the AGNs to contribute substantially to preheat the gas before it falls into clusters, and the quasars to blow some plasma
out of groups and galaxies. 相似文献
5.
获得完备的样本一直是类星体统计分析工作中至关重要的第一步。类星体巡天选择候选体的方法主要有射电波段筛选、色指数筛选、无缝光谱筛选、X射线波段筛选、对红外源或变源进行筛选和零自行的方法。单独运用任一方法都有选择效应,采用多波段方法可以极大地提高样本的完备性。阐述了使用多波段方法选择活动星系核样本的研究现状,提出多波段类星体巡天方法和选源判据,给出ROSAT巡天中F.1002,F.Coma,F.836和F.Leo 4个天区以及空源的15年来X射线选活动星系核的选源和光学新证认的AGN结果,表明多波段类星体巡天方法能有效地提高观测效率。 相似文献
6.
Arati Chokshi 《Journal of Astrophysics and Astronomy》1997,18(4):321-322
A preferred epoch for forming galaxies argues strongly in favour of a standard Big Bang cosmology with a single epoch of creation.
In this paper I present a model in which there is a causal connection between AGN activity and galaxy formation with its epoch
closely linked to the observed epoch of peak AGN activity. 相似文献
7.
A. C. -L. Chian 《Astrophysics and Space Science》1996,242(1-2):249-295
We discuss nonlinear mode-mode coupling phenomena in cosmic plasmas. Four problems are considered: (1) nonlinear three-wave processes in the planetary magnetosphere involving the interaction of auroral Langmuir, Alfvén and whistler waves, (2) nonlinear three-wave processes in the solar wind involving the modulation of Langmuir and electromagnetic waves by ion-acoustic waves, (3) order and chaos in nonlinear four-wave processes in cosmic plasmas, and (4) regular and chaotic dynamics of the relativistic Langmuir turbulence and its application to pulsar and AGN emissions. The observational evidence in support of nonlinear wave-wave interactions in space and astrophysical plasmas is presented. 相似文献
8.
收集了ＢＬＬａｃ天体的有关信息作为前文（Ｆａｎ＆Ｌｉｎ１９９６）的补充,并在文中加入了具有喷流、具有超光速子元和具有高能射线辐射的ＢＬＬａｃ天体表。同时在表１ｃ中列出了ＢＬＬａｃ天体的发射线,对偏振度与大幅光变的统计相关在相对论成束框架下给予了解释。 相似文献
9.
窄线Seyfert1型星系（NLS1）作为活动星系核的一个小类，由于其X射线等高能波段上独特的观测特征，近年来越来越受到天文学界的广泛关注，详细描述了NLS1在观测及理论上的一些新进展，并对其主要模型作了较细致的讨论。 相似文献
10.
蒋栋荣 《中国天文和天体物理学报》1995,(1)
本文对ＶＬＢＩ观测得到的河外射电源致密核ｃｏｒｅ的视角大小进行了统计研究，发现对单个源平均上视角大小近似反比于观测频率，与目前的模型相一致。在５ＧＨｚ上，在红移范围０．０４＜ｚ＜２．５内，平均的ｃｏｒｅ视角大小近似为常数，在非均匀喷流模型框架下，一种可能的解释是在河外射电源致密结构中磁场存在着演化。 相似文献