JHK ′ Imaging Photometry of Seyfert 1 Active Galactic Nuclei and Quasars. III. Variability of Radio‐Quiet and Radio‐Loud Active Galactic Nuclei

Variability of 226 AGNs in the near-infrared $J$, $H$, and $K'$ bands isanalyzed and discussed. An ensemble average for measured variabilities wasobtained for various samples of the AGNs divided by absolute $B$-magnitude$M_B$, redshift $z$, and radio strength. All the samples in the $J$, $H$, and$K'$ bands are found to give significant ensemble variability, but nosignificant wavelength dependence is found. The ensemble variability in theentire sample combining the $J$, $H$, and $K'$ samples is $\Delta m\approx0.22$ mag, while $\Delta m\approx 0.18$ mag for the radio-quiet AGNs and$\Delta m\approx 0.26$ mag for radio-loud AGNs. The ensemble variability forthe radio-quiet AGNs shows no significant $M_B$-dependence, while showingpositive $M_B$-dependence for the radio-loud AGNs. In any samples the measuredvariability shows positive correlation among different passbands, with thecorrelation coefficients of $r_{JH}$, $r_{HK'}$, and $r_{JK'}$ ranging from 0.6to 0.9. For radio-quiet AGNs, the coefficient $r_{HK'}$ in a redshift range of$0.10.3$ and radio-loudAGNs with $z<0.3$, we cannot confirm such strong correlation among differentpassbands. All the features of near-infrared variability for the radio-quietAGNs are consistent with a simple dust reverberation model of the centralregions of AGNs. However, the features for the radio-loud AGNs are not fullyexplained by such a model, and a non-thermal variable component is suggested asa viable candidate for causing their large and fast variability in thenear-infrared region