从事件视界望远镜数据导出的M87喷流底部的磁化程度：测试磁驱动喷流范例
Magnetization degree at the jet base of M87 derived from the event horizon telescope data: Testing magnetically driven jet paradigm
摘要：
利用Doeleman等人在230~GHz的事件视界望远镜（EHT）观测资料，利用Kino等人的方法，探讨了M87喷流底部的磁化程度。我们导出了EHT（EHT区）在其半峰全宽尺寸为$40~{\rm μas}$的致密区中的磁场能量密度（$U_{B}$）和电子、正电子能量密度（$U_{\pm}$）。首先，我们假设在EHT区域中存在同步辐射自吸收（SSA）的光学厚度区域。然后，我们发现，SSA厚的区域不应该太大，不过度产生的坡印廷功率在EHT区。SSA厚区域的角尺寸和磁场强度的允许范围分别为$21~{\rm μas} \le θ_{\rm thick}\le 26.3~{\rm μas}$和$50~{\rm G}\le B_{\rm tot}\le 124~{\rm G}$。相应地，在这种情况下实现了$U_{B}\gg U_{\pm} $。利用Kuo等人在230~GHz的法拉第旋转测量（$RM$）进一步研究了等离子体的组成和质子的能量密度，发现在SSA厚区$U_{B}\gg U_{\pm}+U_{p} $仍然成立.其次，我们研究的情况下，当EHT区域是完全SSA薄。然后我们发现，除非质子是相对论性的，否则$U_{B}\gg U_{\pm}$仍然成立。因此，我们得出结论，磁驱动射流的情况下，在M87是可行的，在接近ISCO尺度的能量，除非EHT区域是完全SSA薄和相对论质子为主。
英文摘要：
We explore the degree of magnetization at the jet base of M87 by using the observational data of the event horizon telescope (EHT) at 230~GHz obtained by Doeleman et al. By utilizing the method in Kino et al., we derive the energy densities of magnetic fields ($U_{B}$) and electrons and positrons ($U_{\pm}$) in the compact region detected by EHT (EHT-region) with its full-width-half-maximum size $40~{\rm μas}$. First, we assume that an optically-thick region for synchrotron self absorption (SSA) exists in the EHT-region. Then, we find that the SSA-thick region should not be too large not to overproduce the Poynting power at the EHT-region. The allowed ranges of the angular size and the magnetic field strength of the SSA-thick region are $21~{\rm μas} \le θ_{\rm thick}\le 26.3~{\rm μas}$ and $50~{\rm G}\le B_{\rm tot}\le 124~{\rm G}$, respectively. Correspondingly $U_{B}\gg U_{\pm} $ is realized in this case. We further examine the composition of plasma and energy density of protons by utilizing the Faraday rotation measurement ($RM$) at 230~GHz obtained by Kuo et al. Then, we find that $U_{B}\gg U_{\pm}+U_{p} $ still holds in the SSA-thick region. Second, we examine the case when EHT-region is fully SSA-thin. Then we find that $U_{B}\gg U_{\pm}$ still holds unless protons are relativistic. Thus, we conclude that magnetically driven jet scenario in M87 is viable in terms of energetics close to ISCO scale unless the EHT-region is fully SSA-thin and relativistic protons dominated.
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