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arXiv 2301.04504astro-ph.HE
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从Fermi-LAT观测中探测到的天鹅茧中的多种发射成分

Multiple emission components in the Cygnus cocoon detected from Fermi-LAT observations

X. Astiasarain, L. Tibaldo., P. Martin, J. Knödlseder, Q. Remy

摘要:

恒星形成区可能在银河系宇宙射线的生命周期中扮演重要角色。对天鹅座X的伽马射线观测揭示了存在过量的硬谱伽马射线发射,可能与新加速粒子的茧有关。基于~13年的观测与费米大面积望远镜(LAT),我们进行了改进的光谱形态学表征的残余排放,包括茧。茧的最佳拟合模型包括两个主要的发射分量:扩展分量FCES G78.74+1.56,由扩展$r_{68} = 4.4^\circ \pm 0.1^\circ\,^{+0.1^\circ}_{-0.1^\circ}$的2D高斯描述,和中心分量FCES G80.00+0.50,由光解离区域的边界内的电离气体的分布追踪。这两个有明显不同的光谱。另外一个扩展发射成分FCES G78.83+3.57位于天鹅座X中央空洞的边缘,其光谱与FCES G80.00+0.50的光谱相一致,可能与茧有关。对于这两个主要组成部分,光谱和径向方位角的发射配置文件可以占在一个扩散损失框架,涉及一个单一的人口的非热粒子。由于从中心源的扩散,粒子跨越FCES G78.74+1.56的全部范围,并且通过与最内部区域中的电离气体相互作用而产生源FCES G80.00+0.50。对于这个简单的扩散损失模型,可行的设置可以是非常不同的能量,运输条件,和所涉及的时间尺度,强子和轻子的情况都是可能的。解决方案的范围从持久的粒子加速,可能在突出的星团,如天鹅座OB 2和NGC 6910,到最近和短暂的粒子释放在过去的10-100 kyr,可能来自超新星遗迹。(节录)

英文摘要:

Star-forming regions may play an important role in the life cycle of Galactic cosmic rays. Gamma-ray observations of Cygnus X have revealed the presence of an excess of hard-spectrum gamma-ray emission, possibly related to a cocoon of freshly accelerated particles. Based on ~13 years of observations with the Fermi-Large Area Telescope (LAT), we performed an improved spectro-morphological characterisation of the residual emission including the cocoon. The best-fit model for the cocoon includes two main emission components: an extended component FCES G78.74+1.56, described by a 2D Gaussian of extension $r_{68} = 4.4^\circ \pm 0.1^\circ\,^{+0.1^\circ}_{-0.1^\circ}$, and a central component FCES G80.00+0.50, traced by the distribution of ionised gas within the borders of the photo-dissociation regions. The two have significantly different spectra. An additional extended emission component FCES G78.83+3.57, located on the edge of the central cavities in Cygnus X and with a spectrum compatible with that of FCES G80.00+0.50, is likely related to the cocoon. For the two main components, spectra and radial-azimuthal profiles of the emission can be accounted for in a diffusion-loss framework involving one single population of non-thermal particles. Particles span the full extent of FCES G78.74+1.56 as a result of diffusion from a central source, and give rise to source FCES G80.00+0.50 by interacting with ionised gas in the innermost region. For this simple diffusion-loss model, viable setups can be very different in terms of energetics, transport conditions, and timescales involved, and both hadronic and leptonic scenarios are possible. The solutions range from long-lasting particle acceleration, possibly in prominent star clusters such as Cyg OB2 and NGC 6910, to a more recent and short-lived release of particles within the last 10-100 kyr, likely from a supernova remnant. (Abridged)

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