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arXiv 2103.08599astro-ph.HEastro-ph.GA
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恒星形成区局部cosmic-ray加速度的双重特征

The double signature of local cosmic-ray acceleration in star-forming regions

Marco Padovani, Alexandre Marcowith, Daniele Galli, Leslie K. Hunt, Francesco Fontani

摘要:

近年来,人们对原恒星表面或沿原恒星喷流的激波产生低能宇宙射线(< 1 TeV)的研究越来越感兴趣。这些局部加速的CR提供了一个有吸引力的解释,高水平的非热发射和电离率,$ζ$,观察接近这些来源。在一些原恒星源中观察到的高$ζ$通常归因于激波产生的紫外光子。本文的目的是表明,当在同一空间区域测量同步辐射和高$ζ$时,局部冲击加速的CR通量足以解释这两种现象。假设相对论粒子按一阶费米加速机制加速,计算了$ζ$和厘米波段的非热辐射。然后,我们将我们的模型应用到恒星形成区域OMC-2 FIR 3/FIR 4。使用贝叶斯分析,我们约束模型的参数和估计的光谱指数的非热无线电发射。我们证明,本地CR加速模型,使它有可能同时解释同步辐射沿HOPS 370喷流在FIR 3区域和$ζ$附近观察到的FIR 4原星团。我们的模型约束的磁场强度(~250-450 $~μ$ G),其湍流分量(~20-40 $~μ$ G),并为HOPS 370喷流(~350-1000 km s $^{-1}$)的三个非热源的冲击参考系中的喷流速度。除了OMC-2 FIR 3/FIR 4系统的建模,我们展示了如何在厘米波长和分子跃迁的连续观测的组合是一个强大的新工具,用于分析恒星形成区域:这两种类型的观测可以同时解释调用只存在局部加速CR,而不必诉诸冲击产生的UV光子。

英文摘要:

Recently, there has been an increased interest in the study of the generation of low-energy cosmic rays (CRs; < 1 TeV) in shocks situated on the surface of a protostar or along protostellar jets. These locally accelerated CRs offer an attractive explanation for the high levels of non-thermal emission and ionisation rate, $ζ$, observed close to these sources. The high $ζ$ observed in some protostellar sources is generally attributed to shock-generated UV photons. The aim of this article is to show that when synchrotron emission and a high $ζ$ are measured in the same spatial region, a locally shock-accelerated CR flux is sufficient to explain both phenomena. We assume that relativistic particles are accelerated according to the first-order Fermi acceleration mechanism and compute $ζ$ and the non-thermal emission at cm wavelengths. We then apply our model to the star-forming region OMC-2 FIR 3/FIR 4. Using a Bayesian analysis, we constrain the parameters of the model and estimate the spectral indices of the non-thermal radio emission. We demonstrate that the local CR acceleration model makes it possible to simultaneously explain the synchrotron emission along the HOPS 370 jet within the FIR 3 region and $ζ$ observed near the FIR 4 protocluster. Our model constrains the magnetic field strength (~250-450$~μ$G), its turbulent component (~20-40$~μ$G), and the jet velocity in the shock reference frame for the three non-thermal sources of the HOPS 370 jet (~350-1000 km s$^{-1}$). Beyond the modelling of the OMC-2 FIR 3/FIR 4 system, we show how the combination of continuum observations at cm wavelengths and molecular transitions is a powerful new tool for the analysis of star-forming regions: these two types of observations can be simultaneously interpreted by invoking only the presence of locally accelerated CRs, without having to resort to shock-generated UV photons.

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