The Cosmic MeV Gamma-Ray Background and Hard X-Ray Spectra of Active Galactic Nuclei: Implications for the Origin of Hot AGN Coronae
The Cosmic MeV Gamma-Ray Background and Hard X-Ray Spectra of Active Galactic Nuclei: Implications for the Origin of Hot AGN Coronae
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DOI：
10.1086/525848
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发表时间：
2007-09
期刊：
影响因子：
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通讯作者：
Y. Inoue;T. Totani;Y. Ueda
中科院分区：
文献类型：
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作者：
Y. Inoue;T. Totani;Y. Ueda
1-10 MeV的河外伽马射线背景辐射的来源仍然未知。虽然高达几百keV的宇宙X射线背景可以用活动星系核（AGN）的总和来解释，但由于模型中假设的电子能量分布的热指数截止，目前的AGN谱模型无法解释超过~1 MeV的背景谱。在这里，我们构建了一个新的光谱模型，通过计算康普顿化过程，包括非热电子，预计存在于活动星系核的热日冕，如果它是由磁重联加热。我们发现，当日冕电子具有非热幂律分量，其总能量是热分量的几个百分比，并且其光谱指数为dln Ne/dln Ee − 4时，我们的模型可以很好地解释MeV背景光谱。虽然在活动星系核附近的光谱中，来自这样一个成分的MeV伽马射线通量低于过去观测的探测极限，但它可能被计划在未来使用的MeV探测器探测到。我们指出，非热分量的总能量和电子指数是相似的，发现在太阳耀斑和地球的磁层，支持重联假说，这反过来又解释了AGN的热日冕的起源磁重联加速电子。
The origin of the extragalactic gamma-ray background radiation at 1-10 MeV is still unknown. Although the cosmic X-ray background up to a few hundred keV can be accounted for by the sum of active galactic nuclei (AGNs), current models of AGN spectra cannot explain the background spectrum beyond ~1 MeV, because of the thermal exponential cutoff of the electron energy distribution assumed in the models. Here we construct a new spectral model by calculating the Comptonization process, including nonthermal electrons, which are expected to exist in an AGN's hot corona if it is heated by magnetic reconnections. We show that the MeV background spectrum can be explained nicely by our model, when coronal electrons have a nonthermal power-law component whose total energy is a few percent of the thermal component and whose spectral index is dln Ne/dln Ee ≈ − 4. Although in nearby AGN spectra the MeV gamma-ray flux from such a component is below the detection limit of past observations, it might be detected by MeV detectors that are planned for future use. We point out that the nonthermal component's total energy and electron index are similar to those found for electrons accelerated by magnetic reconnections in solar flares and in the Earth's magnetosphere, which supports the reconnection hypothesis, which in turn explains the origin of an AGN's hot coronae.