arXiv 0801.36632008-01-23astro-ph

中等质量黑洞活动星系核的X射线辐射

X-ray emission from active galactic nuclei with intermediate mass black holes

G. C. Dewangan, S. Mathur, R. E. Griffiths, A. R. Rao

备注：: 19 pages, ApJ, Submitted
DOI：: 10.1086/591728

摘要：

基于12个XMM-牛顿观测数据，对8个中等质量黑洞（M_BH 8- 95 × 10^4 Msun）活动星系核进行了系统的X射线研究。样本包括这类活动星系核的两个原型--NGC 4395和POX 52，以及SDSS发现的其他六个活动星系核。这些活动星系核具有最强的X射线变化性，在射电宁静的活动星系核中，其归一化的过剩方差最大，功率密度突变时间尺度最短。多余的方差-光度相关似乎取决于BH质量和爱丁顿光度比。破裂时间尺度-黑洞质量关系的活动星系核与IMBH是一致的观察到的大质量活动星系核。我们发现，H β或H α谱线的半高宽与BH质量无关，而与爱丁顿光度比有很强的相关性。四个活动星系核都有明显的软X射线过量辐射（kT_in~150- 200 eV）。另外三个活动星系核的X射线谱与软过剩辐射的存在是一致的。具有最低L/L_Edd的NGC 4395缺乏软过量发射。很明显，小的黑色物质不是活动星系核强软X射线过量发射的主要驱动因素。这些活动星系核的X射线光谱特性和光-X射线光谱能量分布与Seyfert 1星系相似。观测到的IMBH活动星系核的X射线/紫外特性与这些活动星系核是大质量活动星系核的低质量延伸相一致;那些具有高爱丁顿光度比的活动星系核看起来更像窄线Seyfert 1，而那些具有低$L/L_{Edd}$的活动星系核看起来更像宽线Seyfert 1。

英文摘要：

We present a systematic X-ray study of eight AGNs with intermediate mass black holes (M_BH 8-95x10^4 Msun) based on 12 XMM-Newton observations. The sample includes the two prototype AGNs in this class - NGC4395 and POX52 and six other AGNs discovered with the SDSS. These AGNs show some of the strongest X-ray variability with the normalized excess variances being the largest and the power density break time scales being the shortest observed among radio-quiet AGNs. The excess variance -- luminosity correlation appears to depend on both the BH mass and the Eddington luminosity ratio. The break time scale -- black hole mass relations for AGN with IMBHs are consistent with that observed for massive AGNs. We find that the FWHM of the Hbeta or Halpha line is uncorrelated with the BH mass, but shows strong anticorrelation with the Eddington luminosity ratio. Four AGNs show clear evidence for soft X-ray excess emission (kT_in~150-200eV). X-ray spectra of three other AGNs are consistent with the presence of the soft excess emission. NGC4395 with lowest L/L_Edd lacks the soft excess emission. Evidently small black mass is not the primary driver of strong soft X-ray excess emission from AGNs. The X-ray spectral properties and optical-to-X-ray spectral energy distributions of these AGNs are similar to those of Seyfert 1 galaxies. The observed X-ray/UV properties of AGNs with IMBHs are consistent with these AGNs being low mass extension of more massive AGNs; those with high Eddington luminosity ratio looking more like narrow-line Seyfert 1s while those with low $L/L_{Edd}$ looking more like broad-line Seyfert 1s.

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