Blazar喷流电子能谱的一种新的约束方法：Markarian 421事例
A Novel Approach in Constraining Electron Spectra in Blazar Jets: The Case of Markarian 421
摘要：
2008年12月，我们用Swift和Suzaku卫星对TeV耀变体Mrk 421进行了充分研究，并报告了观测结果。在观测过程中，发现Mrk 421处于相对较低的活性状态，其相应的2-10 keV通量为$3 \times 10^{-10}$ erg/s/cm ^2。为了稳健地约束紫外到X射线发射连续谱，我们只选择了与Swift和Suzaku之间真正同时的时间间隔相对应的数据，使我们能够获得高质量的宽带光谱，尽管曝光长度适中（0.6 ksec）。我们分析了光谱与参数的前向拟合SYNCHROTRON模型实现XSPEC假设两种不同的表示的潜在的电子能量分布，以及由当前的粒子加速模型的动机：一个幂律分布以上的最小能量$γ_{\rm min}$与指数截止在最大能量$γ_{\rm max}$，和修改后的超相对论麦克斯韦与平衡能量$γ_{\rm eq}$。我们发现，后者意味着在Mrk 421的耀变体区域内不太可能的物理条件。另一方面，指数调节的幂律电子分布给出了两组可能的模型参数：（i）具有低最小电子能量$γ_{\rm min}<10^3$的平坦谱$dN'_e/dγ\propto γ^{-1.91}$，和（ii）具有高最小电子能量$γ_{\rm min}\simeq 2\times10^4$的陡峭谱$\propto γ^{-2.77}$。我们讨论了不同的解释，这两种可能性的背景下，在相对论，亚或超光速冲击的电子扩散加速。我们还评论如何准确的伽马射线数据可以用来区分所提出的不同的情况。
英文摘要：
We report results from the observations of the well studied TeV blazar Mrk 421 with the Swift and the Suzaku satellites in December 2008. During the observation, Mrk 421 was found in a relatively low activity state, with the corresponding 2-10 keV flux of $3 \times 10^{-10}$ erg/s/cm^2. For the purpose of robust constraining the UV-to-X-ray emission continuum we selected only the data corresponding to truly simultaneous time intervals between Swift and Suzaku, allowing us to obtain a good-quality, broad-band spectrum despite a modest length (0.6 ksec) exposure. We analyzed the spectrum with the parametric forward-fitting SYNCHROTRON model implemented in XSPEC assuming two different representations of the underlying electron energy distribution, both well motivated by the current particle acceleration models: a power-law distribution above the minimum energy $γ_{\rm min}$ with an exponential cutoff at the maximum energy $γ_{\rm max}$, and a modified ultra-relativistic Maxwellian with an equilibrium energy $γ_{\rm eq}$. We found that the latter implies unlikely physical conditions within the blazar zone of Mrk 421. On the other hand, the exponentially moderated power-law electron distribution gives two possible sets of the model parameters: (i) flat spectrum $dN'_e/dγ\propto γ^{-1.91}$ with low minimum electron energy $γ_{\rm min}<10^3$, and (ii) steep spectrum $\propto γ^{-2.77}$ with high minimum electron energy $γ_{\rm min}\simeq 2\times10^4$. We discuss different interpretations of both possibilities in the context of a diffusive acceleration of electrons at relativistic, sub- or superluminal shocks. We also comment on how exactly the gamma-ray data can be used to discriminate between the proposed different scenarios.
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