We present a study of the high-energy properties of the compact symmetric object NGC 4278, recently associated with a TeV source by the Large High Altitude Air Shower Observatory (LHAASO) collaboration. We conducted a dedicated analysis of a Fermi Large Area Telescope (LAT) region around NGC 4278, limited to the LHAASO campaign conducted from 2021 March to 2022 October. A statistically significant emission (∼4.3σ) was revealed, spatially consistent with the radio position of NGC 4278 and the LHAASO source. The Fermi-LAT source is detected above 8 GeV, exhibiting a hard spectrum (photon index Γ = 1.3 ± 0.3) and a γ-ray luminosity of L>100 MeV ≃ 4 × 1041 erg s–1. A serendipitous Swift X-Ray Telescope (XRT) observation of NGC 4278 during the TeV campaign reveals the source in a high state, with a flux , compatible with the highest luminosity level observed in previous Chandra pointings. The high-energy spectral energy distribution of the source and the intense flux variation observed in the X-ray band support a jet origin for the observed radiation. We suggest that the significant enhancement of the high-energy flux observed during the LHAASO campaign is due to a transient, highly energetic perturbation in the jet. The detection of NGC 4278 at both high and very high energies opens new frontiers in studying particle acceleration processes. It reveals that even compact, low-power radio galaxies can exceed the sensitivity thresholds of GeV and TeV instruments, becoming promising targets for the upcoming Cherenkov Telescope Array Observatory.

中文翻译：

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在 LHAASO 活动期间对低光度射电星系 NGC 4278 的费米-LAT 探测


我们提出了一项关于致密对称天体 NGC 4278 的高能特性的研究，该天体最近由大型高空气淋天文台 （LHAASO） 合作与 TeV 源相关联。我们对 NGC 4278 周围的费米大面积望远镜 （LAT） 区域进行了专门分析，仅限于 2021 年 3 月至 2022 年 10 月进行的 LHAASO 活动。揭示了具有统计学意义的发射 （∼4.3σ），在空间上与 NGC 4278 和 LHAASO 源的射电位置一致。费米-LAT 源在 8 GeV 以上被检测到，表现出硬光谱（光子指数 Γ = 1.3 ± 0.3）和 L>100 MeV ≃ 4 × 1041 erg s–1 的γ光度。在 TeV 活动期间，斯威夫特 X 射线望远镜 （XRT） 对 NGC 4278 的偶然观测揭示了该源处于高状态，具有通量，与之前 Chandra 点中观察到的最高光度水平兼容。源的高能光谱能量分布和在 X 射线波段观察到的强烈通量变化支持观察到的辐射的射流来源。我们认为，在 LHAASO 活动期间观察到的高能通量的显着增强是由于喷流中的瞬态、高能扰动。在高能和极高能下检测 NGC 4278 为研究粒子加速过程开辟了新的领域。它揭示了即使是紧凑、低功率的射电星系也可能超过 GeV 和 TeV 仪器的灵敏度阈值，成为即将到来的切伦科夫望远镜阵列天文台的有希望的目标。