标题： 宽波段能量分布的ROSAT探测类星体 II：射电宁静天体 显示英文标题

标题： Broad band energy distribution of ROSAT detected quasars II: Radio-quiet objects

摘要： 一个使用ROSAT检测到的无射电活动类星体数据库被提出，其中包含846个在全天空调查和/或定点PSPC观测中看到的类星体。大约70%的天体是首次在X射线中被检测到。我们提供了软X射线流量和光谱（如果有的话）。利用从该数据库中编译的一个光学选择子样本，我们以高统计显著性研究了无射电活动类星体的宽波段特性。我们确认无射电活动类星体通常比有射电活动的类星体具有更陡的软X射线光谱。光谱差异持续到高红移。在红移约为2的范围内，红移增加导致光谱变平得到了确认，超过这个红移后，光谱斜率似乎与红移无关。红移大于2.5的ROSAT无射电活动类星体的光谱斜率与附近类星体在中等能量带（2-10keV）中的结果一致，这意味着X射线光谱演化并不重要。我们显示，在统计意义上，大多数红移大于2的无射电活动天体几乎没有或没有过量吸收。X射线光度与2500A波长光度之间的相关性得到了证实。个别天体显示出与这一相关性的较大偏差。X射线明亮度alpha_ox似乎与红移无关，但分析表明alpha_ox随着光学光度略有增加。然而，这种行为很可能不是由类星体本身的物理特性引起的，而是固有分散的结果。最后，我们发现一小部分天体相对于其他大部分类星体来说显得相对“X射线安静”。 显示英文摘要

摘要： A database of radio-quiet quasars detected with ROSAT is presented containing 846 quasars seen in the All-Sky Survey and/or in pointed PSPC observations. About 70% of the objects have been detected in X-rays for the first time. We present the soft X-ray fluxes and spectra, if available. Using an optically selected subsample compiled from this database, we study the broad band properties of radio-quiet quasars with high statistical significance. We confirm that radio-quiet quasars have in general steeper soft X-ray spectra than radio-loud. The spectral differences persist to high redshifts. A spectral flattening with increasing redshift is confirmed up to redshift around 2, beyond which the spectral slopes seem to be independent of redshift. The spectral slopes of the ROSAT radio-quiet quasars at z>2.5 are consistent with those found for nearby quasars in the medium energy band (2-10keV), implying that the X-ray spectral evolution is not important. We show that there is, in a statistical sense, little or no excess absorption for most of the radio-quiet objects at z>2. The existence of a correlation between the X-ray luminosity and the luminosity at 2500A is confirmed. Individual objects show a large scatter from this correlation. The X-ray loudness alpha_ox appears to be independent of z, but the analyses indicate a slight increase of alpha_ox with optical luminosity. However, this behavior is likely not caused by physical properties inherent to the quasars but is the result of the intrinsic dispersion. Finally, we find a small fraction of objects which appear to be relatively `X-ray quiet' compared to the bulk of the other quasars.