标题： 塞莱斯蒂亚和帕洛马样本中活动星系核的长期X射线光谱变化通过Swift观测到 显示英文标题

标题： Long-term X-Ray Spectral Variability in AGN from the Palomar sample observed by Swift

摘要： 我们展示了来自附近星系帕洛马样本的24个本地活动星系核（AGN）的X射线光谱变化，主要由Swift观测得到。从硬度比测量中，我们发现18个低吸积率的AGN随着计数率的增加而变硬，这与通常在高吸积率AGN中观察到的“越亮越软”行为相反。两个AGN随着计数率的增加而变软，两个表现出更复杂的行为，两个没有显示出任何简单的关系。有足够的数据将13个AGN的光谱按通量分箱进行叠加。在这9个源中，幂律成分的光子指数（$\Gamma$）的亮度相关变化是硬度变化的主要原因。对于6个对象，其吸积率作为爱丁顿率的比例（ṁ$\mathrm{_{Edd}}$），$\Gamma$与 ṁ$\mathrm{_{Edd}}$呈反相关，即观察到了“越亮越硬”的行为。3个较高ṁ$\mathrm{_{Edd}}$率的对象显示了$\Gamma$与 ṁ$\mathrm{_{Edd}}$之间的正相关。 这种从低ṁ$\mathrm{_{Edd}}$时的更亮更硬到高ṁ$\mathrm{_{Edd}}$时的更亮更软的转变，可以通过X射线辐射的主要种子光子来源从日冕本身的回旋同步辐射转变为吸积盘的热种子光子来解释。 这种转变在黑洞X射线双星（BHXRBs）的“硬态”中也可见。 结果支持了LINERs是处于硬态的BHXRBs的类似物，而塞弗特星系则是处于BHXRBs的高吸积率端的硬态或硬中间态的类似物的观点。 显示英文摘要

摘要： We present X-ray spectral variability of 24 local active galactic nuclei (AGN) from the Palomar sample of nearby galaxies, as observed mainly by Swift. From hardness ratio measurements, we find that 18 AGN with low accretion rates show hardening with increasing count rate, converse to the softer-when-brighter behaviour normally observed in AGN with higher accretion rates. Two AGN show softening with increasing count rate, two show more complex behaviour, and two do not show any simple relationship. Sufficient data were available for the spectra of 13 AGN to be summed in flux-bins. In 9 of these sources, correlated luminosity-dependent changes in the photon index ($\Gamma$) of a power-law component are found to be the main cause of hardness variability. For 6 objects, with a low accretion rate as a fraction of the Eddington rate (\.m$\mathrm{_{Edd}}$), $\Gamma$ is anticorrelated with \.m$\mathrm{_{Edd}}$, i.e. `harder-when-brighter' behaviour is observed. The 3 higher-\.m$\mathrm{_{Edd}}$-rate objects show a positive correlation between $\Gamma$ and \.m$\mathrm{_{Edd}}$. This transition from harder-when-brighter at low \.m$\mathrm{_{Edd}}$s to softer-when-brighter at high \.m$\mathrm{_{Edd}}$s can be explained by a change in the dominant source of seed-photons for X-ray emission from cyclo-synchrotron emission from the Comptonising corona itself to thermal seed-photons from the accretion disc. This transition is also seen in the `hard state' of black hole X-ray binaries (BHXRBs). The results support the idea that LINERs are analogues of BHXRBs in the hard state and that Seyferts are analogues of BHXRBs in either the high-accretion-rate end of the hard state or in the hard-intermediate state.