年轻疏散星团中的Gamma-ray产生：Berk 87，Cyg OB2和Westerlund 2
Gamma-ray production in young open clusters: Berk 87, Cyg OB2 and Westerlund 2
摘要：
年轻的疏散星团很可能是宇宙射线加速的场所，最近在两个疏散星团（天鹅座OB 2和韦斯特伦德2）方向上探测到的TeV伽马射线源以及它们与一些未识别的EGRET源的方向接近表明了这一点。事实上，到目前为止，人们已经考虑了疏散星团内粒子加速的几种不同情况，即大质量星风中的激波、双星及其星云、超新星激波、大质量致密双星。在这里，我们详细考虑由于电子和强子加速内的疏散星团的辐射过程。作为一个具体的情况下，我们应用的加速过程中所产生的WR型恒星的风的冲击。在WR星年龄定义的加速场景的活动时间内，粒子通过疏散星团的介质扩散。它们与物质和辐射相互作用，首先在疏散星团内，然后在周围稠密的云层中。我们计算了三个疏散星团（Berk 87，Cyg OB 2，Westerlund 2）在不同过程中的宽带光谱，这些星团的光谱具有目前最好的观测约束。假设从X射线到GeV-TeV伽马射线能量所观察到的高能现象是相互关联的。我们的结论是，在这些对象中的辐射过程的最有可能的描述是在混合（轻子-强子）模型，其中轻子是负责所观察到的X射线和GeV的伽马射线发射和强子是负责TeV的伽马射线发射，这是直接产生的内部和周围的疏散星团密集的云。
英文摘要：
Young open clusters are likely sites of cosmic ray acceleration as indicated by recent detections of the TeV gamma-ray sources in the directions of two open clusters (Cyg OB2 and Westerlund 2) and their directional proximity to some unidentified EGRET sources. In fact, up to now a few different scenarios for acceleration of particles inside open clusters have been considered, i.e. shocks in massive star winds, pulsars and their nebulae, supernova shocks, massive compact binaries. Here we consider in detail the radiation processes due to both electrons and hadrons accelerated inside the open cluster. As a specific scenario, we apply the acceleration process at the shocks arising in the winds of WR type stars. Particles diffuse through the medium of the open cluster during the activity time of the acceleration scenario defined by the age of the WR star. They interact with the matter and radiation, at first inside the open cluster and, later in the dense surrounding clouds. We calculate the broad band spectrum in different processes for three example open clusters (Berk 87, Cyg OB2, Westerlund 2) for which the best observational constraints on the spectra are at present available. It is assumed that the high energy phenomena, observed from the X-ray up to the GeV-TeV gamma-ray energies, are related to each other. We conclude that the most likely description of the radiation processes in these objects is achieved in the hybrid (leptonic-hadronic) model in which leptons are responsible for the observed X-ray and GeV gamma-ray emission and hadrons are responsible for the TeV gamma-ray emission, which is produced directly inside and in dense clouds surrounding the open cluster.
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