耀变体S4 0954+65在2025年初的异常伽马射线耀发活动
Exceptional Gamma-Ray Flaring Activity of the Blazar S4 0954+65 in Early 2025
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中文总结 AI 辅助
针对耀变体S4 0954+65在2025年初的异常伽马射线耀发，通过多波段观测与建模，揭示其由喷流内新扰动传播驱动，并支持轻子辐射模型。
中文摘要 AI 辅助
S4 0954+65（4FGL J0958.7+6534）是一个红移为 $z = 0.3694 \pm 0.0011$ 的TeV探测耀变体，被归类为中间同步辐射峰值的BL Lac天体。2025年初，它进入了一个异常的 $\gamma$-射线高态。我们旨在研究2025年异常耀发的起源和物理性质，并约束导致此次耀发活动的辐射过程。我们利用 $\gamma$-射线、X射线、光学/紫外、射电以及43 GHz甚长基线阵列（VLBA）观测进行了多波段分析。我们使用z变换离散相关函数（zDCF）检查了多波段相关性，分析了光谱演化和秒差距尺度喷流运动学，并对宽带光谱能量分布（SEDs）进行了建模。$\gamma$-射线变化分别领先光学和射电辐射3.22天和可能的18.26天，而 $\gamma$-射线与X射线发射之间未发现显著相关性。$\gamma$-射线光谱表现出越亮越硬的特性，与活动状态期间增强的粒子加速一致。在X射线波段也观察到类似的光谱趋势，其中光子指数与通量呈反相关。在主要的 $\gamma$-射线耀发期间，VLBA图像揭示了从核心出现一个新的超光速射电节点，其外推喷射时间与 $\gamma$-射线耀发的峰值一致。2025年耀发期间的时间和结构演化与喷流内激波情景一致，其中新出现的扰动向下游传播并驱动耀发。宽带SED建模表明，一个轻子同步自康普顿加外部康普顿模型，包含尘埃环种子光子，以物理上合理的参数重现了多波段观测。轻子-强子解释仍然可能，但需要显著更高的喷流功率。
英文摘要
S4 0954+65 (4FGL J0958.7+6534) is a TeV-detected blazar at a redshift of $z = 0.3694 \pm 0.0011$, classified as an intermediate-synchrotron-peaked BL Lac object. In early 2025, it entered an exceptional $γ$-ray high state. We aim to investigate the origin and physical properties of the exceptional 2025 flare, and to constrain the emission processes responsible for this flaring activity. We performed a multi-wavelength analysis using $γ$-ray, X-ray, optical/UV, radio, and 43 GHz Very Long Baseline Array (VLBA) observations. We examined multi-band correlations with the z-transformed discrete correlation function (zDCF), analyzed the spectral evolution and parsec-scale jet kinematics, and modeled the broadband spectral energy distributions (SEDs). The $γ$-ray variations lead the optical and radio emission by 3.22 days and possibly 18.26 days, respectively, while no significant correlation is found between the $γ$-ray and X-ray emission. The $γ$-ray spectra show a harder-when-brighter behavior, consistent with enhanced particle acceleration during the active state. A similar spectral trend is also observed in the X-ray band, where the photon index is anti-correlated with flux. During the major $γ$-ray flare, VLBA images reveal the emergence of a new superluminal radio knot from the core, whose extrapolated ejection time is consistent with the peak of the $γ$-ray flare. The temporal and structural evolution during the 2025 flare is consistent with a shock-in-jet scenario, in which a newly emerging disturbance propagates downstream and drives the flare. Broadband SED modeling shows that a leptonic synchrotron self-Compton plus external Compton model with dusty torus seed photons reproduces the multi-wavelength observations with physically plausible parameters. A lepto-hadronic interpretation remains possible but requires substantially higher jet power.
发表机构
- Shanghai Normal University（上海师范大学）
- Sun Yat-sen University（中山大学）
- Yunnan Observatories（云南天文台）
- National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）
机构由 AI 辅助整理，请以论文原文为准。
