The relationship between variable and polarized optical spectral components of luminous type 1 non-blazar quasars
The relationship between variable and polarized optical spectral components of luminous type 1 non-blazar quasars
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DOI：
10.1093/pasj/psw050
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发表时间：
2016-04
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影响因子：
--
通讯作者：
M. Kokubo
中科院分区：
文献类型：
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作者：
M. Kokubo
Kishimoto 等人进行的光学光谱偏振测定。 (2004) 表明，几个发光 1 型类星体在 $\lambda<4000$A 的静止坐标近紫外波长中表现出偏振连续通量的强烈减少。在文献中，这种光谱特征被解释为由于吸积盘大气不透明效应而印在吸积盘热发射中的氢巴尔默吸收边变宽的证据。另一方面，类星体通量变异性研究表明，类星体紫外光谱中的可变连续谱分量被认为是吸积盘发射的固有光谱形状的良好指标，通常在整个近紫外到光学光谱范围内具有明显平坦的光谱形状。为了检验偏振通量和可变分量光谱所揭示的圆盘连续光谱形状是否彼此一致，我们对 Kishimoto 等人的四个偏振减弱类星体样本进行了多波段光度监测观测。 (2004) (4C09.72、3C323.1、Ton 202 和 B2 1208+32) 导出可变分量光谱，并将它们的光谱形状与偏振通量光谱的光谱形状进行比较。与预期相反，我们确认这些类星体的两个光谱分量具有完全不同的光谱形状，因为与偏振通量光谱相比，可变分量光谱明显更蓝。光谱形状的这种差异可能意味着（1）静止帧紫外波长中偏振度的降低并不表明巴尔默吸收边缘特征，而是由一些未知（去）偏振机制引起的，或者（2）紫外光通量变化优先发生在吸积盘的热内半径处，因此可变分量光谱不反映整个吸积盘发射。
Optical spectropolarimetry carried out by Kishimoto et al. (2004) has shown that several luminous type 1 quasars show a strong decrease of the polarized continuum flux in the rest-frame near-UV wavelengths of $\lambda<4000$A. In the literature, this spectral feature is interpreted as evidence of the broadened hydrogen Balmer absorption edge imprinted in the accretion disk thermal emission due to the disk atmospheric opacity effect. On the other hand, the quasar flux variability studies have shown that the variable continuum component in UV-optical spectra of quasars, which is considered to be a good indicator of the intrinsic spectral shape of the accretion disk emission, generally have significantly flat spectral shape throughout the near-UV to optical spectral range. To examine whether the disk continuum spectral shapes revealed as the polarized flux and as the variable component spectra are consistent with each other, we carry out multi-band photometric monitoring observations for a sample of four polarization-decreasing quasars of Kishimoto et al. (2004) (4C09.72, 3C323.1, Ton 202, and B2 1208+32) to derive the variable component spectra and compare the spectral shape of them with that of the polarized flux spectra. Contrary to expectation, we confirm that the two spectral components of these quasars have totally different spectral shape in that the variable component spectra are significantly bluer compared to the polarized flux spectra. This discrepancy in the spectral shape may imply either (1) the decrease of polarization degree in the rest-frame UV wavelengths is not indicating the Balmer absorption edge feature but is induced by some unknown (de)polarization mechanisms, or (2) the UV-optical flux variability is occurring preferentially at the hot inner radii of the accretion disk and thus the variable component spectra do not reflect the whole accretion disk emission.