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arXiv 1507.02440astro-ph.HE
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相对论和次相对论宇宙射线在100 pc中心区的谱

Spectrum of Relativistic and Subrelativistic Cosmic Rays in the 100 pc Central Region

V. A. Dogiel, D. O. Chernyshov, A. M. Kiselev, M. Nobukawa, K. S. Cheng, C. Y. Hui, C. M. Ko, K. K. Nobukawa, T. G. Tsuru

摘要:

从氢电离率和γ射线通量出发,导出了银河系中心(GC)附近的分子云Sgr B2内部和附近的相对论性和亚相对论性宇宙射线(CR)谱。我们研究了分子云中的CR传播的两种情况:自由传播和中性气体湍流激发的磁涨落对粒子的散射。我们表明,在后一种情况下,CR在云中的传播可以描述为扩散系数为$\sim 3\times 10^{27}$ cm $^2$ s $^{-1}$。对于亚相对论质子电离氢的情况,我们用谱指数$δ>-1$证明了它们在云外的谱是相当硬的。亚相对论质子的能量密度($>50$ eV cm $^{-3}$)比相对论CR高一个数量级。这些质子从Sgr B2产生6.4 keV的发射,这大约是朱雀在2013年观察到的通量的30%。2013年以后的观测可能会发现Sgr B2中的次相对论CR产生的背景通量。或者,Sgr B2中分子气体的氢离子化可能由高能电子引起。我们表明,电子韧致辐射的光谱比从Sgr B2观察到的连续谱更硬,并且原则上,从INTEGRAL数据中可以看出,电子提供的X射线分量在观察到的光谱$E_x^{-2}$之上是一个稳定的高能量过剩。

英文摘要:

From the rate of hydrogen ionization and the gamma ray flux, we derived the spectrum of relativistic and subrelativistic cosmic rays (CRs) nearby and inside the molecular cloud Sgr B2 near the Galactic Center (GC). We studied two cases of CR propagation in molecular clouds: free propagation and scattering of particles by magnetic fluctuations excited by the neutral gas turbulence. We showed that in the latter case CR propagation inside the cloud can be described as diffusion with the coefficient $\sim 3\times 10^{27}$ cm$^2$ s$^{-1}$. For the case of hydrogen ionization by subrelativistic protons, we showed that their spectrum outside the cloud is quite hard with the spectral index $δ>-1$. The energy density of subrelativistic protons ($>50$ eV cm$^{-3}$) is one order of magnitude higher than that of relativistic CRs. These protons generate the 6.4 keV emission from Sgr B2, which was about 30\% of the flux observed by Suzaku in 2013. Future observations for the period after 2013 may discover the background flux generated by subrelativistic CRs in Sgr B2. Alternatively hydrogen ionization of the molecular gas in Sgr B2 may be caused by high energy electrons. We showed that the spectrum of electron bremsstrahlung is harder than the observed continuum from Sgr B2, and in principle this X-ray component provided by electrons could be seen from the INTEGRAL data as a stationary high energy excess above the observed spectrum $E_x^{-2}$.

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