类星体的X射线辐射研究

由爱因斯坦天文台最近观测到的273个类星体、Ⅰ型Seyfeft星系的软X射线光度(L_x为0.5—4.5keV)资料,与它们的红移z值构成一个连续序列(图1)。利用球对称吸积模型计算得到:高红移的类星体,由于其较大的吸积率,在这个序列上停留的时间较短(～106年);而低红移类星体及Ⅰ型Seyfert星系停留的时间较长(～108年)。利用现有的107个类星体的射电单色光度l_r,光学单色光度l_o以及X射线单色光度l_x的资料,讨论了类星体大尺度谱的硬度,发现类星体的光学光度有两个不同的演化阶段;文中还定性地讨论了类星体射电辐射机制不同于光学和射电辐射的机制之处。 

X-RAY STUDIES OF QUASARS

In this paper,a statistical study is made of the evolution of X-ray radiation of 273 objects (235 quasars and 38 type I Seyferts) in the 0.5-4.5 keVband observed from the Einstein Observatory.On the L_x-z plot of these 273 objects,there seems to exist a natural physical sequence (the QE band),which connects the active galaxies such as quasars and Seyferts in the sense of energy and the mass distribution of the central compact objects (hence the distribution of accretion rates).On the basis of the spherically symmetric accretion model of a massive black hole,the preliminary analysis of this sequence shows that quasars may quickly cross the lower envelope of the QE band and leave it and then disappear.Due to large accretion rates,the time of staying on this QE band for high-redshift quasars is found to be comparatively short (～106yr),while that for low-redshift quasars and type I Seyferts is longer (～108yr).These results agree with observations.Therefore,active galactic nuclei such as quasars and Seyferts may be manifestations of galactic nuclei in an excited state under specific conditions.Using the available monochromatic radio,optical and X-ray luminosities l_r l_o and l_x of 107 quasars,we find that there exist two evolutionary stages in the optical luminosities of quasars: the optically bright and optically faint stages.In each of these stages,the parameters characterizing the typical properties of quasars are evidently distinctive.The change of spectrum types may imply that the radiation mechanisms in different energy regions are different.