Multiple Regression Analysis of the Variable Component in the Near-Infrared Region for Type 1 AGN MCG +08-11-011

We propose a new method of analysing a variable component for type 1 activegalactic nuclei (AGNs) in the near-infrared wavelength region. This analysisuses a multiple regression technique and divides the variable component intotwo components originating in the accretion disk at the center of AGNs and fromthe dust torus that far surrounds the disk. Applying this analysis to thelong-term $VHK$ monitoring data of MCG+08-11-011 that were obtained by theMAGNUM project, we found that the $(H-K)$-color temperature of the dustcomponent is $T = 1635$K $\pm20$K, which agrees with the sublimationtemperature of dust grains, and that the time delay of $K$ to $H$ variations is$\Delta t\approx 6$ days, which indicates the existence of a radial temperaturegradient in the dust torus. As for the disk component, we found that thepower-law spectrum of $f_\nu \propto \nu^\alpha$ in the $V$ to near-infrared$HK$ bands varies with a fixed index of $\alpha\approx -0.1$ -- +0.4, which isbroadly consistent with the irradiated standard disk model. The outer part ofthe disk therefore extends out to a radial distance where the temperaturedecreases to radiate the light in the near-infrared.Comment: 10pages + 5figures, accepted by ApJ