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arXiv 1504.01908astro-ph.HE
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Gamma-Ray亮射电星系的Suzaku和Fermi观测:X射线发射的起源和宽带模拟

Suzaku and Fermi Observations of Gamma-Ray Bright Radio Galaxies: Origin of the X-ray Emission and Broad-Band Modeling

Y. Fukazawa, S. Tokuda, R. Itoh, Y. Tanaka, J. Finke, L. Stawarz

摘要:

我们用{ \em Suzaku}对八个邻近的$γ$射线亮射电星系进行了系统的X射线研究,以了解它们的X射线发射起源。其中五个的{ \em Suzaku}光谱以前已经给出,而其余三个(M1,87、PKS 1,0625、$-$ 354和3C 1,78)在此首次给出。基于铁-钾线强度,X射线的变化,和X射线幂律光子指数,并使用额外的信息上的[O III]线发射,我们认为在这三个源中观察到的X射线发射的喷射起源。我们还分析了五年的{ \em Fermi}大面积望远镜(LAT)对PKS 1,0625 $-$ 354和3C 1,78的GeV伽马射线数据,以了解blazar图片中的这些来源。我们在前一个物体中发现了显著的$γ$射线变化。总的来说,我们注意到PKS 1,0625 $-$ 354和3C 1,78的{ \em Suzaku}光谱相当软,而LAT光谱与其他$γ$射线探测到的低功率(FR\,I)射电星系相比异常硬。我们证明了所构造的PKS 1,0625、$-$ 354和3C 1,78的宽带光谱能量分布可以用单区同步辐射/同步辐射自康普顿模型很好地描述。建模的结果表明,较低的体积洛伦兹因子相比,通常发现在其他BL Lac对象,但与其他LAT检测FR\,I射电星系建模推断的值一致。有趣的是,建模也意味着非常高的峰值($\sim 10^{16}$ \,Hz)的同步加速器频率在两个分析的来源,相反,先前建议的方案FR I/BL Lac统一。我们讨论的背景下,FR\,I/BL Lac统一计划的影响,我们的研究结果。

英文摘要:

We performed a systematic X-ray study of eight nearby $γ$-ray bright radio galaxies with {\em Suzaku} for understanding the origin of their X-ray emissions. The {\em Suzaku} spectra for five of those have been presented previously, while the remaining three (M\,87, PKS\,0625$-$354, and 3C\,78) are presented here for the first time. Based on the Fe-K line strength, X-ray variability, and X-ray power-law photon indices, and using additional information on the [O III] line emission, we argue for a jet origin of the observed X-ray emission in these three sources. We also analyzed five years of {\em Fermi} Large Area Telescope (LAT) GeV gamma-ray data on PKS\,0625$-$354 and 3C\,78 to understand these sources within the blazar picture. We found significant $γ$-ray variability in the former object. Overall, we note that the {\em Suzaku} spectra for both PKS\,0625$-$354 and 3C\,78 are rather soft, while the LAT spectra are unusually hard when compared with other $γ$-ray detected low-power (FR\,I) radio galaxies. We demonstrate that the constructed broad-band spectral energy distributions of PKS\,0625$-$354 and 3C\,78 are well described by a one-zone synchrotron/synchrotron self-Compton model. The results of the modeling indicate lower bulk Lorentz factors compared to those typically found in other BL Lac objects, but consistent with the values inferred from modeling other LAT-detected FR\,I radio galaxies. Interestingly, the modeling also implies very high peak ($\sim 10^{16}$\,Hz) synchrotron frequencies in the two analyzed sources, contrary to previously-suggested scenarios for FR I/BL Lac unification. We discuss the implications of our findings in the context of the FR\,I/BL Lac unification schemes.

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