窄线赛弗特Ⅰ型星系中可能具有吸积盘热辐射起源的软X射线超

NLSIs with Soft X-ray Excess of Possible Disk Origin

理论上,低质量高吸积率活动星系核的标准吸积盘黑体热辐射有可能形成软X射线波段的超出。然而,活动星系核的软X射线超温度为0.1 keV左右,显著高于标准吸积盘理论预言的最高有效温度。只有Yuan等人在2010年报道的RX J1633+4718是一个例外,其软超温度为32.5_(-6.0)^(+8.0) eV,显著小于0.1 keV,并与吸积盘理论预言的温度相符;此外,其光度也符合吸积盘的理论预期。因此该软X射线超很可能起源于吸积盘的热辐射。这一类源对于吸积盘理论和软X射线超的研究都有重要意义。文中使用ROSATPSPC数据,在所有已知的窄线赛弗特Ⅰ型星系(Narrow Line SeyfertⅠgalaxies,NLSIs)中寻找类似于RX J1633+4718的源,即软X射线超可能起源于吸积盘热辐射的源。分析了150个源的245条光谱,其中58个源的90条光谱具有显著的软X射线超。样本中软X射线超温度分布的平均值T_(soft)为0.10keV,标准偏差为0.03 keV。除了RX J1633+4718外,只有3个源的软X射线超温度小于60 eV,而且温度接近吸积盘最高温度。这个结果表明,类似于RX J1633+4718的具有低温软X射线超的源很稀少。最后,在具有黑洞质量估计的26个源中,软超温度与黑洞质量M_(BH)、爱丁顿比L/LEdd及预期吸积盘最高温度T_(max)都没有明显的关联性,与前人的结果一致。

It is theoretically expected that the thermal radiation from accretion disks of Active Galactic Nuclei （AGNs） with low black hole mass would contribute to the soft X-ray band and result in an excess emission. However, the temperatures of the observed soft X-ray excess of AGNs are typically around 0.1 keV, significantly higher than those predicted by the standard disk model. There is only one exception found so far, RX J1633＋4718, which has a significantly low soft excess temperature of 32.5＋8.0-6.0~ eV, consistent with the maximum temperature as well as the luminosity of the predicted disk emission（Yuan et al. 2010）. In this paper, we search for RX J1633 like AGNs, whose soft X-ray excess temperature is close to the maximum temperature of accretion disk, in all known Narrow Line Seyfert I galaxies （NLSIs） observed with ROSAT PSPC in the archive. We analyzed the PSPC spectra of 150 NLSIs （245 observations） in total, 58 （90 observations） of which show significantly soft X-ray excess emission. In addition to RX J1633＋4718, only 3 objects （4 observations） show soft X-ray excess temperatures less than 60 eV and close to the theoretical prediction of the disk emission. They form a sample of candidates for future follow-up studies. Our result indicates that RX J1633＋4718 like objects are very rare. The correlations between the temperature of the soft X-ray excess and black hole mass as well as the Eddington ratio are also investigated, and no correlation is found. This confirms the previous results, and implies that the soft X-ray excess of most AGNs should originate from other mechanisms rather than the thermal emission of the accretion disk.