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arXiv 1508.02589astro-ph.HE
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IRAS 13224-3809中软X射线过量的变异性

Variability of the soft X-ray excess in IRAS 13224-3809

E. S. Kammoun, I. E. Papadakis, B. M. Sabra

备注：
Accepted for publication in A&A, 10 pages, 7 figures
发表信息：
A&A 582, A40 (2015)
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摘要：

研究了窄线赛弗特1星系IRAS 13224-3809的软超变。我们考虑了所有五个存档的XMM-牛顿观测，并应用了“通量-通量图”（FFP）方法。我们发现，通量通量图的光变曲线的时间仓大小的选择受到很大的影响，最有可能是因为快速和大幅度的变化，和内在的非线性通量通量-通量关系在这个源。因此，我们建议在这种情况下使用最小的bin大小。因此，我们在1.7 keV以下的11个能带中构建了FFP，并且我们认为1.7-3 keV带代表初级发射。FFP合理地很好地拟合了“幂律加常数”模型。我们在五次观测中的三次中检测到显著的正常数。在低于$\sim 0.9$ keV的能量下，最佳拟合斜率比单位更平坦，其中软过剩最强。这表明存在固有的光谱变异性。一个幂律的主分量，这是可变的流量和光谱斜率（如$Γ\propto N_{\rm PL}^{0.1}$）和软过剩分量，这是随着主连续（如$F_{\rm excess}\propto F_{\rm primary}^{0.46}$），可以广泛地解释FFP。事实上，即使在不存在稳定的光谱分量时，这也可以产生正的“常数”。尽管如此，一个稳定的，软带常数分量的可能性不能排除，但它的贡献所观察到的0.2-1千电子伏带通量应小于$\sim 15$ %。在FFP的模型常数是一致的，在一个观察为零，在另一个能量低于1千电子伏的负。很难在任何光谱变化情况下解释这些结果，但它们可能意味着在源中存在可变的暖吸收体。

英文摘要：

We study the soft excess variability of the narrow line Seyfert 1 galaxy IRAS 13224-3809. We considered all five archival XMM-Newton observations, and we applied the 'flux-flux plot' (FFP) method. We found that the flux-flux plots were highly affected by the choice of the light curves' time bin size, most probably because of the fast and large amplitude variations, and the intrinsic non-linear flux--flux relations in this source. Therefore, we recommend that the smallest bin-size should be used in such cases. Hence, We constructed FFPs in 11 energy bands below 1.7 keV, and we considered the 1.7-3 keV band, as being representative of the primary emission. The FFPs are reasonably well fitted by a 'power-law plus a constant' model. We detected significant positive constants in three out of five observations. The best-fit slopes are flatter than unity at energies below $\sim 0.9$ keV, where the soft excess is strongest. This suggests the presence of intrinsic spectral variability. A power-law-like primary component, which is variable in flux and spectral slope (as $Γ\propto N_{\rm PL}^{0.1}$) and a soft-excess component, which varies with the primary continuum (as $F_{\rm excess}\propto F_{\rm primary}^{0.46}$), can broadly explain the FFPs. In fact, this can create positive `constants', even when a stable spectral component does not exist. Nevertheless, the possibility of a stable, soft--band constant component cannot be ruled out, but its contribution to the observed 0.2-1 keV band flux should be less than $\sim 15$ %. The model constants in the FFPs were consistent with zero in one observation, and negative at energies below 1 keV in another. It is hard to explain these results in the context of any spectral variability scenario, but they may signify the presence of a variable, warm absorber in the source.

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