W51 复合体中粒子辐照与激波-云相互作用产生的伽马射线
Gamma-ray emission from particle illumination and shock-cloud interaction in the W51 Complex
AI总结：
本研究针对 W51 复合体，通过建模激波-云相互作用与粒子辐照两种场景，发现辐照场景可解释 LHAASO 观测到的超高能伽马辐射，确定致密分子环境是维持拍电子伏加速器活动的关键结构。
AI中文摘要：
在甚高能（VHE）与超高能（UHE）伽马射线天文学的当前时代，理解银河系 PeVatron（拍电子伏加速器）及其加速机制仍是核心目标。近期 LHAASO（高海拔宇宙线观测站）对 W51 复合体的观测使其成为研究 UHE 辐射起源的理想实验室，尤其是该复合体中存在围绕多个潜在粒子加速器的大质量、致密分子环境。本研究针对 W51 复合体探讨两种强子场景：其一，对 SNR（超新星遗迹）W51C 与 W51B 中邻近云的直接相互作用进行建模，纳入新鲜粒子加速、激波驱动的绝热压缩及弥漫银河系宇宙线的再加速过程；其二，探究一种不依赖加速器的辐照场景，其中 W51B 云作为早期注入的高能粒子的长期束缚区域。研究发现，直接激波-云相互作用场景可成功复现 Fermi-LAT（费米大视场望远镜）观测到的 GeV 辐射，但无法解释 LHAASO 探测到的 UHE 辐射；相比之下，辐照场景能自然解释 UHE 能谱，表明致密分子云可在长时间尺度上有效束缚并维持高能强子种群。尽管推断的注入历史与年轻 SNR 起源相符，但辐照框架的非源依赖性也允许 W51 复合体内部存在其他加速器。因此，本研究结果确定致密分子环境是维持历史 PeVatron 活动并塑造观测到的 UHE 伽马射线辐射的关键结构。
英文摘要：
In the current era of very-high-energy (VHE) and ultra-high-energy (UHE) $γ$-ray astronomy, understanding Galactic PeVatrons and their acceleration mechanisms remains a primary objective. Recent LHAASO observations of the W51 Complex make it an ideal laboratory for investigating the origin of UHE emission, particularly due to the presence of massive and dense molecular environment surrounding multiple potential particle accelerators. In this work, we study two hadronic scenarios for the W51 Complex. First, we model the direct interaction between the SNR W51C and the nearby clouds in W51B, incorporating fresh particle acceleration, shock-driven adiabatic compression, and reacceleration of permeating Galactic cosmic rays. Second, we explore an accelerator-independent illumination scenario in which the W51B cloud acts as a long-term confinement region for high-energy particles injected during an earlier epoch. We find that the direct shock-cloud interaction scenario successfully reproduces the GeV emission observed by Fermi-LAT, but fails to account for the UHE emission detected by LHAASO. In contrast, the illumination scenario naturally explains the UHE spectrum, indicating that dense molecular clouds can efficiently confine and sustain energetic hadronic populations over long timescales. Although the inferred injection history is compatible with a young SNR origin, the source-independent nature of the illumination framework also permits other accelerators within the W51 Complex. Our results therefore identify dense molecular environments as the key structures sustaining historical PeVatron activity and shaping the observed UHE $γ$-ray emission.
