用INTEGRAL SPI观测Cen A的硬X射线连续谱
The hard X-ray continuum of Cen A observed with INTEGRAL SPI
摘要：
利用INTEGRAL SPI对半人马座A活动星系核的硬X射线谱进行了10年的观测。这个源在SPI带通（23 keV-8 MeV）中具有从任何活动星系核观测到的最高通量。提出了Cen A的10年光变曲线，硬度比证实，光谱形状变化很小，尽管光度变化的几个因素。首先，我们建立了一个反射组件的平均光谱中的存在下，通过展示20-60千电子伏之间的过剩，从扩展在低能量下观察到的SPI制度的光谱形状。Chandra HETGS和INTEGRAL SPI数据中的过量部分通过中性光学厚度大气中占主导地位的幂律光谱的反射得到了很好的描述。我们发现，再处理的排放贡献20-25%的23-100 keV的通量。在几十到几百keV的截止值的存在仍然存在争议。使用模拟光谱，我们表明，高能量截止再现所观察到的光谱性质的岑A更容易比一个简单的幂律。然而，我们还表明，这样的截止可能被低估时忽略（即使是适度的）反射，并为Cen A将在能量>700 keV，置信度> 95%。这对于AGN中观察到的热康普顿化等离子体来说是非常高的，我们建议我们实际上是在模拟同步加速器自康普顿光谱预期的光谱形状的更渐进的变化。
英文摘要：
We revisit the average hard X-ray spectrum from the AGN of Centaurus A (Cen A) using ten years worth of observations with INTEGRAL SPI. This source has the highest flux observed from any AGN in the SPI bandpass (23 keV--8 MeV). The 10 year lightcurve of Cen A is presented, and hardness ratios confirm that the spectral shape changes very little despite the luminosity varying by a factor of a few. Primarily, we establish the presence of a reflection component in the average spectrum by demonstrating an excess between 20-60 keV, from extending the spectral shape observed at low energy to the SPI regime. The excess in Chandra HETGS and INTEGRAL SPI data is well described by reflection of the dominant power law spectrum from a neutral, optically-thick atmosphere. We find that the reprocessed emission contributes 20-25% of the 23-100 keV flux. The existence of a cut-off at tens to hundreds of keV remains controversial. Using simulated spectra, we demonstrate that a high energy cut off reproduces the observed spectral properties of Cen A more readily than a simple power law. However, we also show that such a cut-off is probably underestimated when neglecting (even modest) reflection, and for Cen A would be at energies >700 keV, with a confidence of >95%. This is atypically high for thermal Comptonizing plasmas observed in AGN, and we propose that we are in fact modelling the more gradual change in spectral shape expected of synchrotron self-Compton spectra.
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