Abstract Radio galaxies host relativistic jets oriented away from our line of sight, making them challenging targets for Very High Energy (VHE, E > 100 GeV) γ-ray detectors. Indeed, out of ∼ 100 extragalactic sources detected at E > 100 GeV, only six are radio galaxies, while the great majority are blazars hosting aligned jets. The new Cherenkov Telescope Array (CTA) will provide order-of-magnitude improvements in sensitivity and spectral resolution with respect to the present generation of ground-based γ-ray observatories, opening new frontiers for high-energy studies of radio galaxies. In a previous paper, we studied the detection prospects of misaligned jets with the CTA for a sample of sources from the Third Fermi-LAT catalog (3FGL). In this work, we complement this study taking advantage of the expanded sample from the Fourth Fermi-LAT catalog (4FGL), which includes roughly double the number of sources. We simulate CTA observations of 41 γ-ray radio galaxies, extrapolating their Fermi-LAT spectrum into the TeV energy range assuming different spectral shapes. We predict that the CTA will detect eleven new TeV radio galaxies with an observational campaign of 50 hours per source, under the realistic assumption of a spectral cutoff at 0.5 TeV. This would increase the sample of VHE radio galaxies by a factor of three, and result in the first detection of FR II radio galaxies at these energies. By simulating CTA observations with 5 h exposure, we predict that two Fermi-LAT radio galaxies should already be well within reach of current TeV observatories. Finally we have investigated the prospects for a CTA detection of extended VHE emission from the lobe-dominated FR I Fornax A, and predict that such a detection will be possible for integration times ≳ 50 h. We conclude that, in line with our previous findings, the CTA will significantly impact our understanding of misaligned jets at TeV energies, allowing us to perform population studies, as well as a comparison between the two main radio galaxy subclasses for the first time in this energy band.

中文翻译：

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重新审视射电星系的 TeV 探测前景

摘要 射电星系拥有远离我们视线的相对论喷流，这使得它们成为超高能 (VHE，E > 100 GeV) γ 射线探测器的挑战性目标。事实上，在 E > 100 GeV 探测到的大约 100 个河外源中，只有 6 个是射电星系，而绝大多数是拥有对齐喷流的耀变体。新的切伦科夫望远镜阵列 (CTA) 将在灵敏度和光谱分辨率方面提供数量级的改进，与当代地面 γ 射线天文台相比，为射电星系的高能研究开辟了新的领域。在之前的一篇论文中，我们使用 CTA 研究了对来自第三费米-LAT 目录 (3FGL) 的源样本的未对准射流的检测前景。在这项工作中，我们利用来自第四费米 LAT 目录 (4FGL) 的扩展样本对这项研究进行了补充，其中包括大约两倍的来源数量。我们模拟了 41 个 γ 射线射电星系的 CTA 观测，假设不同的光谱形状，将它们的 Fermi-LAT 光谱外推到 TeV 能量范围。我们预测，在光谱截止频率为 0.5 TeV 的现实假设下，CTA 将探测到 11 个新的 TeV 射电星系，每个源的观测活动为 50 小时。这将使 VHE 射电星系的样本增加三倍，并导致在这些能量下首次探测到 FR II 射电星系。通过模拟暴露 5 小时的 CTA 观测，我们预测两个 Fermi-LAT 射电星系应该已经在当前 TeV 天文台的范围内。最后，我们研究了 CTA 检测来自叶主导的 FR I Fornax A 的扩展 VHE 发射的前景，并预测这种检测在积分时间 ≳ 50 小时内是可能的。我们得出的结论是，与我们之前的发现一致，CTA 将显着影响我们对 TeV 能量未对准射流的理解，使我们能够进行种群研究，以及在本次研究中首次对两个主要射电星系亚类进行比较。能量带。