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arXiv 2207.01065astro-ph.HE
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Arakelian 120中UV/X射线关系的起源

Origins of the UV/X-ray Relation in Arakelian 120

Ra'ad David Mahmoud, Chris Done, Delphine Porquet, Andrew Lobban

摘要:

我们利用\textit{Swift}的紫外和X射线观测研究了Arakelian 120中的吸积几何。硬X射线($1-10$ keV)显示出大幅度、快速(几天)的变化,因此我们预计来自光盘的混响会从变化的硬X射线照明中产生UV变化。我们模型的光谱能量分布,包括一个外标准盘(光学),一个中间温暖的Comptonisation区(UV和软X射线)和热日冕(硬X射线)。与较低的爱丁顿部分AGN(NGC 4151和NGC 5548分别位于$L/L_{Edd}\sim 0.02$和$0.03$)不同,Akn 120($L\sim 0.05L_{Edd}$)的SED由紫外线主导,仅通过能量限制了反射硬X射线的影响。高度为$\sim10 R_g$的硬X射线电晕的照明产生最小的UV变化。将冠状刻度高度增加到$\sim 100 R_g$可改善与观察到的UV变化幅度的匹配,因为圆盘对向较大的立体角,但会导致太快的变化而无法匹配UV数据。软X射线(在温暖的康普顿化模型中与紫外线相连)比硬X射线的变化更大,但同样包含太多的快速变化,无法与紫外线中观察到的更平滑的变化相匹配。较低的爱丁顿分数AGN的结果强调了混响从更大的尺度(宽线区域)的贡献,但混响引起的延迟相似的时间尺度上的平滑,产生更大的延迟比是兼容的数据。我们的结论是,大多数的紫外线的变化,因此是内在的,连接到质量吸积率波动在温暖的康普顿化区域。

英文摘要:

We explore the accretion geometry in Arakelian 120 using intensive UV and X-ray monitoring from \textit{Swift}. The hard X-rays ($1-10$ keV) show large amplitude, fast (few-day) variability, so we expect reverberation from the disc to produce UV variability from the varying hard X-ray illumination. We model the spectral energy distribution including an outer standard disc (optical), an intermediate warm Comptonisation region (UV and soft X-ray) and a hot corona (hard X-rays). Unlike the lower Eddington fraction AGN (NGC 4151 and NGC 5548 at $L/L_{Edd}\sim 0.02$ and $0.03$ respectively), the SED of Akn 120 ($L\sim 0.05L_{Edd}$) is dominated by the UV, restricting the impact of reverberating hard X-rays by energetics alone. Illumination from a hard X-ray corona with height $\sim10 R_g$ produces minimal UV variability. Increasing the coronal scale height to $\sim 100 R_g$ improves the match to the observed amplitude of UV variability as the disc subtends a larger solid angle, but results in too much fast variability to match the UV data. The soft X-rays (connected to the UV in the warm Comptonisation model) are more variable than the hard, but again contain too much fast variability to match the observed smoother variability seen in the UV. Results on lower Eddington fraction AGN have emphasised the contribution from reverberation from larger scales (the broad line region), but reverberation induces lags on similar timescales to the smoothing, producing a larger delay than is compatible with the data. We conclude that the majority of the UV variability is therefore intrinsic, connected to mass accretion rate fluctuations in the warm Comptonisation region.

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