用离散相关函数方法分析Blazar天体的γ射线和射电辐射的相关性

收集了119颗有γ射线噪的Blazar天体样品(97个平谱射电类星体和22个BL Lac天体)，用离散相关函数(DCF)方法分析了1GeV γ射线辐射流量(最大值、最小值和平均值)与8.4GHz射电辐射流量之间的相关性.获得的主要结果为：在119个Blazar天体和97个平谱射电类星体中，γ射线辐射流量的最大值以及平均值和射电辐射流量之间有相关性;而γ射线辐射流量的最小值和射电辐射流量之间没有相关性.本文结果表明，γ射线和射电辐射都来自喷流，γ射线很可能产生于同步自康普顿(SSC)过程. 关键词： Blazar γ射线 射电辐射 流量密度     

BL Lac天体的γ射线和射电辐射的统计特性

给出了一个带有射电5.0GHz，8.4GHz 和γ射线辐射流量密度的22个γ噪BL Lac天体的样本，研究了它们在1GeV处的γ射线辐射流量密度最大值、平均值及最小值与射电5.0GHz，8.4GHz辐射流量之间的可能关系.结果表明：1）射电5.0GHz，8.4GHz辐射与γ射线辐射在低态时没有相关，但在高态和平均态时都存在较强的相关，最大相关系数r=0.85，置信度均好于10^-4；2）γ射线谱指数和射电谱指数之间也有一个弱相关关系存在.因此，认为γ射线的辐射主要是同步自康普顿辐射. 关键词： BL Lac天体 γ射线 射电辐射 谱指数     

基于Logistic回归模型的Blazar天体的分类

从文献中收集了205个Blazar天体,包括142个BL Lac天体和63个平谱射电类星体(FSRQs).对这些天体的类别与它们的红移、射电5 GHz辐射流量、光学V波段流量、1 keV处X射线流量、X射线光子谱指数进行了相关性和Logistic回归分析.结果表明,对Blazar天体分类产生主要影响的因素是红移、射电5 GHz辐射流量和X射线光子谱指数,综合应用这三个物理量判别Blazar天体的分类的准确率可达到91.2%,得到的分类方程具有良好的预测效果,可以作为Blazar天体分类的一个重要的判据.而光学V波段流量和1 keV处X射线流量不能区分开BL Lac天体和FSRQs,它们与Blazar天体分类没有相关性.本文结果支持将BL Lac天体和FSRQs归为Blazar天体,不同类别的Blazar天体之间能通过一种演化序列相联系. 关键词： Logistic 分类 Blazar天体     

RBLs与XBLs的多波段流量及中心黑洞质量的研究

BL Lacs天体的辐射谱变化、多波段的相关性及偏振的特性为研究各辐射分量的内禀相互关联提供重要的信息.本文用收集了RBLs和XBLs的红移、中心黑洞质量,统计得到RBLs天体的红移大于XBLs天体,RBLs天体的平均中心黑洞质量小于XBLs天体的平均中心黑洞质量.本文还收集了低态时射电波段、红外波段、光学波段及X射线波段的辐射流量,并分析了它们之间的相关性,及其与红移的相关性.本文的结果支持了RBLs和XBLs可作为BL Lac天体的有效分类标准的观点,并且表明它们的物理性质可能存在差异,而非选择效应的 关键词： BL Lac天体 多波段辐射流量     

基于聚合经验模态分解方法的OJ 287 射电流量变化周期分析

BL Lac 天体OJ 287 是一个重要的Blazar天体, 光变具有准周期特点. 本文从密歇根大学射电天文台数据库收集了OJ 287射电波段4.8, 8.0和 14.5 GHz超过30年时间的观测数据. 由于天文观测资料的复杂性, 一些传统寻找周期的方法不是太理想. 近几年迅速发展起来的聚合经验模态分解(EEMD) 特别适合于具有非线性和非平稳动态变化特性的Blazar天体光变规律的研究. 运用EEMD方法对OJ 287 的3个射电波段流量分别进行多时间尺度分解, 各获得6个代表不同时间尺度局部特征信息的本征模态函数分量和一个趋势项. 研究结果表明: 4.8 GHz射电流量变化的主要周期是18.9, 11.9, 5.7 和2.4年; 8.0 GHz 的主要周期是12.2, 5.2和2.4 年; 14.5 GHz的主要周期是21.8, 12.0, 4.3和 2.4 年. 尽管3个波段流量变化主要周期大小有一定的差别, 但是存在着近似相同的变化周期12.0 和2.4年, 说明这3个波段可能来源于相同的辐射机制, 也证实了OJ 287 射电波段和光学波段具有相同的长光变周期12.0 年. 这些结论表明: EEMD 作为一种全新的非线性、非平稳信号处理方法, 可以更精确地提取Blazar天体中不同光变周期的分量. 关键词： OJ 287 光变周期 聚合经验模态分解     

长时γ暴和短时γ暴的脉冲辐射

采用小波分析方法对康普顿γ射线天文台 (CGRO)上的BATSE仪器观测到的γ暴光变曲线数据进行去噪处理 ,并提出更有效的脉冲识别算法 ,然后用对齐叠加方式分别计算长暴和短暴光变曲线的主脉冲的平均辐射曲线和归一化的平均脉冲辐射曲线。统计结果表明两类暴的平均辐射曲线有显著的差异性 ,而归一化的平均脉冲辐射曲线差异不大。这个结果意味着两类暴的暴源可能有本质的差异 ,但两类暴的辐射机制没有根本区别。这个结果进一步支持了把γ暴分为长暴和短暴两类暴的分类办法 ,同时解释了为什么γ暴的持续时间有非常显著的分类特征 ,但其它观测量在两类暴中没有体现出明显的分类特征的问题。     

宽吸收线类星体物理研究

现在普遍相信类星体的反馈会调节寄主星系形成的进程,但其中具体的物理过程依然是个谜.类星体的外流是一个重要的候选者.为了确定外流的重要性,中国科学技术大学天体物理中心开展了宽吸收线类星体的一系列研究,取得了一些进展: (1)宽吸收线区的紫外吸收物质的柱密度比原来预计高出2个量级,低电离吸收线形成于饱和的高电离吸收线区;(2)射电宁静的宽吸收类星体吸收物质主要在赤道面,并且不同的源吸收物质分布情况很不相同,而在射电强的类星体中,赤道和极向外流都是可能的;(3)共振散射线偏振表明,外流物质携带角动量.     

脉冲γ射线对光纤的辐射效应

介绍了光纤的损耗机制和γ射线对光纤的辐射效应,设计了针对脉冲γ射线作用于光纤而产生辐射感生损耗的实验测量系统。利用平均光子能量为0.3 MeV、脉冲宽度25 ns、剂量率2.03×107Gy.s-1,和平均光子能量为1.0 MeV、脉冲宽度25 ns、剂量率5.32×109Gy.s-1的2种脉冲γ射线分别作用于多模和单模光纤,分别采用波长为405,660,850,1 310和1 550 nm的激光光纤传输系统对辐射感生损耗进行了测量。获得了光纤辐射感生损耗和辐射剂量的关系,并对实验结果进行分析。从实验结果可以看出:在近红外到可见光范围内,脉冲γ射线对光纤作用产生的辐射感生损耗随探测波长减小而增大;在0.1~3.5 Gy剂量范围内,多模光纤辐射感生损耗和辐射剂量呈线性关系。分析辐射对光纤的作用机制和实验结果后得出:光纤基质原子的电子能级对传输光子的共振吸收而造成吸收损耗增加;光纤折射率分布的改变从而导致波导损耗增加。     

GAMMA-RAY AND X-RAY EMISSION FROM GAMMA-RAY-LOUD BLAZARS

We present a strong correlation of the gamma-ray (above 100 MeV) mean spectral indices α_γ and X-ray (1 keV) mean spectral indices α_X for 34 gamma-ray-loud blazars (16 BL Lac objects and 18 flat spectrum radio quasars). A strong correlation is also found between the gamma-ray flux densities F_γ and X-ray flux densities F_X in the low state for 47 blazars (17 BL Lac and 30 flat spectrum radio quasars). Possible correlation on the gamma-ray emission mechanism is discussed. We suggest that the main gamma-ray radiation mechanism is probably the synchrotron process. The gamma-ray emission may be somewhat different from that of BL Lac objects and flat spectrum radio quasars.     

Radio waves and γ-ray emission from astrophysical sources

A mechanism of X- and γ-ray emission by relativistic electrons at interaction with astrophysical objects (maser clouds) is considered and the contribution of this mechanism to the formation of a continuous spectrum and its correlation with radio-wave radiation are investigated. The radiation yield upon deexcitation of a quantum system by an electron exceeds that of “conventional” (i.e., without a change in the quantum-system state) bremsstrahlung at small nuclear charges (Z < 10) and may be about 8% of the total γ-ray intensity. It is shown that in the direction in which the γ-ray intensity increases, one should observe radio waves corresponding to a particular maser source.     

Statistical properties of extragalactic radio sources

In this paper, a large sample of extragalactic radio sources is analysed to show their statistical properties. The core and total radio powers are used to determine the core-dominance parameter for galaxies, BL Lacertae objects and quasars; mutual correlations between core radio power, total radio power, redshift and core dominance parameter are examined for different subclasses. A statistically significant correlation between the total and core radio power is confirmed. There are no obvious correlations between core-dominance parameter and the total power for our whole sample and quasars, but there is a statistically significant anti-correlation for our galaxy sample. Some discussions and comparison of the correlations with those obtained by other authors are also given.     

The AGNs and the extragalactic gamma ray background

The first part of this paper describes the identification of γ-ray AGNs. The database of cosmic γ-rays above 100 MeV from the SAS-2 satellite has been analysed to identify γ-ray emissions from 11 quasars, 3 BL Lac Objects and 1 radiogalaxy. Further investigations of the relationship between their γ-ray fluxes in different energy regions (>100 MeV and 35-100 MeV) and the relationship between their γ-ray fluxes and their redshifts, support that the sources detected are genuine extragalactic objects.The second part of this paper describes the determination of the contribution from AGNs to the extragalactic γ-ray background. The SAS-2 γ-ray data have been employed to determine the functional relationships between the absolute γ-ray luminosities L_γ and the absolute optical luminosities of quasars andSeyfert galaxies. From these, their contribution to the extragalaxtic γ-ray background can be derived. We have shown that quasars (B<20) and Seyfert (Type 1 and 1.5) galaxies together contribute to a substantial part (about 59%) of the diffuse γ-ray background in the 35-100 MeV range. Therefore we conclude that the extragalactic γ-ray background is likely to be generated by active galaxies such as quasars and Seyfert galaxies.     

Observation of active galactic nuclei on the GT-48 CrAO γ-ray telescope in 2004

The results of observations of active galactic nuclei on the γ-ray telescope GT-48 (Crimean Astrophysical Observatory) in 2004 are reported. Fluxes of very-high-energy γ rays (E ≥ 10¹² eV) from the 3C 66A, Mkn 421, Mkn 501, and 1H 1426 objects have been recorded at a level exceeding 4σ. The upper values of γ-ray fluxes for the active nuclei of the 1ES 1959 and BL Lac galactics are presented. Analysis of the data on the 3C66A object confirmed the existence of γ-ray fluxes from this source. This object was previously discovered in Crimea.     

Relativistic beaming effect for blazars

In this paper, we revisit the relationship between the spectral index and the core-dominance parameter using a larger sample of 157 blazars (23 BL Lacertae objects and 134 flat spectrum radio quasars), compiled from the available literature. From the relevant data, we find the spectral index associated with the core-dominance parameter, for which a relativistic beaming effect is responsible. In addition, we make a comparison of the properties between BL Lacertae objects and flat spectrum radio quasars.