平谱射电类星体4C 50.11的高能性质
High energy properties of the flat spectrum radio quasar 4C 50.11
摘要：
研究了红移为$z= 1.517$的平谱射电类星体（FSRQ）4c 50的$γ$射线和X射线性质。{ \it Fermi}大面积望远镜（LAT）的数据表明，该源自2013年7月以来一直处于活跃状态。在活跃期间，$γ$射线通量增加了三倍以上，并检测到两个不同的耀斑，其变化时间尺度短至几个小时。$γ$射线谱可用对数抛物线拟合。通过拟合，我们发现了$γ$射线谱的峰值能量与谱曲率之间的相关性，这在blazar的$γ$射线辐射中尚属首次。{ \it Swift} X射线望远镜（XRT）的数据显示，该源在X射线能量上是可变的，但没有证据表明与$γ$射线活动有关的通量或光谱变化。用{ \it Swift} XRT和{ \it NuSTAR}获得的宽带X射线谱由破缺PL模型很好地描述，其中极硬谱（$Γ_{1} \sim 0.1$）低于破缺能量，$E_{\rm break} \sim 2.1 {\rm keV}$和$Γ_{2} \sim 1.5$高于破缺能量。低于$\sim 3$ keV的光谱陡峭可能是由于发射光子的电子群的能量分布中的低能截止。当更亮时，$γ$射线和X射线发射都显得更硬。宽带光谱能量分布（SED）的源，我们提供了一个模型拟合的SED。我们的模拟表明，发射区应该在宽线区之外，并且该区域的性质表明在激活状态下有42%的爱丁顿功率的喷流。
英文摘要：
We investigate the $γ$-ray and X-ray properties of the flat spectrum radio quasar (FSRQ) \4c50 at redshift $z= 1.517$. The {\it Fermi} Large Area Telescope (LAT) data indicate that this source was in an active state since 2013 July. During the active period, the $γ$-ray flux increased by more than a factor of three and two distinct flares were detected with the variability timescale as short as several hours. The $γ$-ray spectra can be well fitted by a log-parabola. From the fitting, we find a correlation between the peak energy and spectral curvature for the $γ$-ray spectra, which is the first time seen in $γ$-ray emission from a blazar. The {\it Swift} X-ray Telescope (XRT) data show that the source was variable at X-ray energies, but no evidence shows flux or spectral changes related to the $γ$-ray activity. The broad-band X-ray spectrum obtained with {\it Swift} XRT and {\it NuSTAR} is well described by a broken PL model, with an extremely hard spectrum ($Γ_{1} \sim 0.1$) below the break energy, $E_{\rm break} \sim 2.1 {\rm keV}$, and $Γ_{2} \sim 1.5$ above the break energy. The spectral steepening below $\sim 3$ keV is likely due to the low energy cut-off in the energy distribution of the photon-emitting electron population. Both the $γ$-ray and X-ray emission appear harder when brighter. The broad-band spectral energy distribution (SED) is constructed for the source, and we provide a model fit to the SED. Our modeling suggests that the emission region should be outside the broad line region, and the properties of the region indicate a jet with 42\% of the Eddington power during the active state.
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