Constraints on accretion disk size in the massive type 1 quasar PG 2308+098 from optical continuum reverberation lags
Constraints on accretion disk size in the massive type 1 quasar PG 2308+098 from optical continuum reverberation lags
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DOI：
10.1093/pasj/psy096
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发表时间：
2018-07
影响因子：
2.3
通讯作者：
M. Kokubo
中科院分区：
文献类型：
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作者：
M. Kokubo
利用1.05米Kiso施密特望远镜/Kiso宽视场照相机获得了Z=0.433的大质量1型类星体PG 2308+098两年的u-、g-、r-、i-和z-波段光学光变曲线，并测量了光变曲线的带间时间滞后。在g-，r-，i-和z-波段检测到相对于u-波段几十天的波长相关连续混响滞后信号，其中较长的波长波段显示出较大的滞后。根据波长相关的滞后，并假设标准盘温度径向分布T \propto R_{\rm disk}^{-3/4}$和X射线/远紫外再处理图片，对2500 AA盘连续辐射的吸积盘半径的约束为：R_{\rm盘} = 9.46^{+0.29}_{-3.12}$ light-天导出的盘的大小是略大于（1.2-1.8倍）的理论盘的大小$R_{\rm磁盘} = 5.46$光天预测的黑洞质量（$M_{\rm BH}$）和爱丁顿比估计PG 2308+098。这一结果是大致按照以前的研究较低质量的活动星系核（AGN），其中测量的磁盘大小已被发现是大于标准磁盘模型预测的一个因素的$\sim 3$，然而，磁盘大小的差异是更温和的PG 2308+098。通过对AGN/类星体的连续混响观测和引力微透镜观测中的圆盘尺寸约束的文献值的整理，我们发现，圆盘尺寸对引力微透镜的依赖性比标准圆盘模型的依赖性弱.这些观测结果表明，标准的Shakura-Sunyaev吸积盘理论在描述活动星系核/类星体吸积盘时存在局限性。
Two years' worth of u-, g-, r-, i-, and z-band optical light curves were obtained for the massive type 1 quasar PG 2308+098 at z=0.433 using the 1.05-m Kiso Schmidt telescope/Kiso Wide Field Camera, and inter-band time lags of the light curves were measured. Wavelength-dependent continuum reverberation lag signals of several tens of days relative to the u-band were detected at g-, r-, i-, and z-bands, where the longer wavelength bands showed larger lags. From the wavelength-dependent lags, and assuming the standard disk temperature radial profile $T \propto R_{\rm disk}^{-3/4}$ and an X-ray/far-ultraviolet reprocessing picture, a constraint on the radius of the accretion disk responsible for the rest-frame 2500 \AA\ disk continuum emission was derived as $R_{\rm disk} = 9.46^{+0.29}_{-3.12}$ light-days. The derived disk size is slightly (1.2-1.8 times) larger than the theoretical disk size of $R_{\rm disk} = 5.46$ light-days predicted from the black hole mass ($M_{\rm BH}$) and Eddington ratio estimates of PG 2308+098. This result is roughly in accordance with previous studies of lower mass active galactic nuclei (AGNs), where measured disk sizes have been found to be larger than the standard disk model predictions by a factor of $\sim 3$; however, the disk size discrepancy is more modest in PG 2308+098. By compiling literature values of the disk size constraints from continuum reverberation and gravitational microlensing observations for AGNs/quasars, we show that the $M_{\rm BH}$ dependence of $R_{\rm disk}$ is weaker than that expected from the standard disk model. These observations suggest that the standard Shakura-Sunyaev accretion disk theory has limitations in describing AGN/quasar accretion disks.