利用JVLA、LOFAR、e-Merlin、VLBA和EVN对RBS 797的研究：双超大质量黑洞能否解释中央射电星系的爆发历史？
A JVLA, LOFAR, e-Merlin, VLBA and EVN study of RBS 797: can binary SMBHs explain the outburst history of the central radio galaxy?
AI总结：
本研究利用多台射电望远镜的多频段多尺度数据，探究RBS 797中央射电星系的结构与爆发历史，通过分析喷流进动等特征，提出双超大质量黑洞可能是其垂直爆发等现象的成因。
摘要：
我们利用JVLA、LOFAR（含国际站）、e-Merlin、VLBA和EVN数据，对RBS 797的中央射电星系开展了多频段（144 MHz–9 GHz）、多尺度（5 pc–50 kpc）研究。我们探究了射电瓣、喷流和活动核心的形态与光谱特征，证实了射电瓣与四个垂直X射线空腔（见arXiv:2111.03679）的空间重合性。东西向射电瓣的辐射年龄（$31.4\pm6.6$ Myr）与南北向射电瓣的辐射年龄（$32.1\pm9.9$ Myr）支持垂直爆发具有同源起源，且二者的活动阶段持续时间相近（$\sim$12 Myr）。对于尺度为$\leq10$ kpc的内部南北向喷流，我们：（a）证实了其S形喷流形态；（b）发现每条喷流存在两个光谱指数相近的热点；（c）估算出扭曲喷流的年龄小于$\sim8$ Myr。基于这些结果，我们确定周期为$\sim$9 Myr、半张角为$\sim$24$^{\circ}$、喷流速度为$\sim$0.01$c$的喷流进动，能够解释南北向喷流的特征。我们还发现，同步辐射注入指数从规模更大、更古老的爆发（$Γ\sim0.5$）到更年轻的S形喷流（$Γ\sim0.9$）呈现变陡趋势，这可能是由于活动模式从类FR I型向类FR II型转变所致。VLBI数据显示，RBS 797中心存在一个致密的单核心，其周围环绕着延展射电辐射，辐射的取向取决于数据采样的空间尺度。我们探讨了多种基于中心引擎的情景来解释这些结果。综合现有证据，我们认为RBS 797很可能存在（或曾经存在）双活动超大质量黑洞。这与VLBI数据仅探测到单一成分的结果仍相一致，因为预测的双超大质量黑洞间距（$\leq$0.6 pc）比现有射电数据的分辨率（5 pc）小一个数量级。
英文摘要：
We present a multi-frequency (144 MHz - 9 GHz) and multi-scale (5 pc - 50 kpc) investigation of the central radio galaxy in RBS 797, by means of JVLA, LOFAR (with international stations), e-Merlin, VLBA and EVN data. We investigate the morphological and spectral properties of the radio lobes, the jets, and the active core. We confirm the co-spatiality of the radio lobes with the four perpendicular X-ray cavities (see arXiv:2111.03679). The radiative ages of the E-W lobes ($31.4\pm6.6$ Myr) and of the N-S lobes ($32.1\pm9.9$ Myr) support a coeval origin of the perpendicular outbursts, that also have similar active phase duration ($\sim$12 Myr). For the inner N-S jets (on scales of $\leq10$ kpc), we (a) confirm the S-shaped jet morphology; (b) show the presence of two hotspots per jet with a similar spectral index; (c) estimate the age of the twisting jets to be less than $\sim8$ Myr. Based on these results, we determine that jet precession, with period $\sim$9 Myr, half-opening angle $\sim$24$^{\circ}$ and jet speed $\sim$0.01$c$, can explain the properties of the N-S jets. We also find that the synchrotron injection index has steepened from the large, older outbursts ($Γ\sim0.5$) to the younger S-shaped jets ($Γ\sim0.9$), possibly due to a transition from an FR I-like to an FR II-like activity. The VLBI data reveal a single, compact core at the heart of RBS 797, surrounded by extended radio emission whose orientation depends on the spatial scale sampled by the data. We explore several engine-based scenarios to explain these results. Piecing together the available evidence, we argue that RBS 797 likely hosts (or hosted) binary active SMBHs. This is still consistent with the detection of a single component in the VLBI data, since the predicted separation of the binary SMBHs ($\leq$0.6 pc) is an order of magnitude smaller than the resolution of the available radio data (5 pc).
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