γ-ray production in young open clusters: Berk 87, Cyg OB2 and Westerlund 2
γ-ray production in young open clusters: Berk 87, Cyg OB2 and Westerlund 2
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年轻疏散星团中的 γ 射线产生：Berk 87、Cyg OB2 和 Westerlund 2
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发表时间：
2007
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影响因子：
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通讯作者：
W. Bednarek
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作者：
W. Bednarek
年轻的疏散星团是宇宙射线加速的场所，最近在两个疏散星团（Cyg OB 2和Westerlund 2）的方向上探测到TeV γ射线源。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，即大质量星星风中的激波、恒星及其星云、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在疏散星团内加速的辐射过程。作为一个具体的情况下，我们应用的加速过程中产生的冲击风的沃尔夫-拉叶（WR）型恒星。在WR星星的年龄所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。它们首先在疏散星系团内部，然后在周围稠密的云层中与物质和辐射相互作用。我们计算了三个典型的疏散星团（Berk 87，Cyg OB 2，Westerlund 2）在不同的过程中的宽带光谱，其光谱上的最佳观测约束目前可用。假设从X射线到GeV-TeV γ射线能量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实现在混合（轻子-强子）模型，其中轻子负责所观察到的X射线和GeV的γ射线发射和强子负责TeV的γ射线发射。
Young open clusters are sites of cosmic ray acceleration as indicated by recent detections of the TeV γ-ray sources in the directions of two open clusters (Cyg OB2 and Westerlund 2). 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 Wolf-Rayet (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 exemplary 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 γ-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 γ-ray emission and hadrons are responsible for the TeV γ-ray emission.