AI 中文总结
本研究发现致密陡谱类星体3C 138于2024-2026年爆发，通过多波段观测揭示其射电、X射线、光学、γ射线的演化特征，提出单区SSC模型可解释其能谱，支持核主导活跃阶段的相关结论。
AI 中文摘要
在经历了数十年的相对宁静期后，致密陡谱类星体3C 138于2024-2026年进入活跃阶段，表现出强烈的宽带耀发。我们利用RATAN-600和RT-32在1-22 GHz频段的密集多频射电监测、Zeiss-1000和AS-500/2的光学R波段观测、Swift/XRT和SRG/ART-XC的X射线测量，以及Fermi-LAT的γ射线光变曲线，研究其多波段行为。2022年后射电增亮加速，且在最高频率处最为显著；射电谱明显变硬，11-22 GHz的谱指数在活跃阶段从陡变平或反转。2025-2026年X射线流量增长超过3倍，光子指数从Γ_X≈1.6变硬至Γ_X≈0.9，峰值后又变软。耀发分解显示，活跃后期出现5次γ射线耀发和一系列光学次耀发；γ射线、X射线和光学的峰值出现在约13天的区间内，表明是同一活动事件，而射电增亮则更缓慢且与频率相关。在采用的致密区几何下，稀疏的两态能谱（SED）可用单区同步自康普顿（SSC）解表示，外康普顿（EC）的相对贡献则取决于几何。该耀发使模型能量分配向相对论电子偏移，结果支持存在一个更持久的核主导活跃阶段，后期的高能和光学耀发叠加在新兴同步辐射成分的不透明度驱动射电演化之上。
英文摘要
After several decades of relative quiescence, the compact steep-spectrum quasar 3C 138 entered an active phase in 2024-2026, exhibiting strong broadband flaring. We investigate its multiwavelength behaviour using dense multifrequency radio monitoring at 1-22 GHz with RATAN-600 and RT-32, optical R-band observations with Zeiss-1000 and AS-500/2, X-ray measurements with Swift/XRT and SRG/ART-XC, and the Fermi-LAT $γ$-ray light curve. The radio brightening accelerated after 2022 and was strongest at the highest frequencies. The radio spectra hardened markedly, with the 11-22 GHz spectral index evolving from steep to flat or inverted during the active phase. The X-ray flux increased by more than a factor of three during 2025-2026, while the photon index hardened from $Γ_{\rm X}\simeq 1.6$ to $Γ_{\rm X}\simeq 0.9$ and softened back after the peak. Flare decomposition revealed five $γ$-ray flares and a sequence of optical subflares during the later stages of the activity. The $γ$-ray, X-ray, and optical maxima occur within a $\simeq 13$-day interval, suggesting a common activity episode, whereas the radio brightens more gradually and in a frequency-dependent manner. Under the adopted compact-zone geometries, the sparse two-state spectral energy distributions (SEDs) can be represented by one-zone synchrotron self-Compton (SSC) solutions, while the relative contribution of external Compton (EC) remains geometry dependent. The flare shifts the modelled energy partition towards relativistic electrons. These results favour a longer-lived, core-dominated activity phase, with later high-energy and optical flares superposed on the opacity-driven radio evolution of an emerging synchrotron component.
Comments20 pages, 12 figures. Submitted to MNRAS
