Mid-infrared Ensemble Variability of Broad-line and Narrow-line Seyfert 1 Galaxies

Abstract We utilized multiepoch archival data from the Wide-field Infrared Survey Explorer to compare the variability at 3.4 μ m (W1 band) and 4.6 μ m (W2 band) of broad-line Seyfert 1 (BLSy1) galaxies and narrow-line Seyfert 1 (NLSy1) galaxies by employing the ensemble structure function (SF). Additionally, we investigated the dependence of mid-infrared (MIR) ensemble SF on common active galactic nucleus parameters. The main results are as follows. (1) The ensemble SF of BLSy1 galaxies is larger than that of NLSy1 galaxies at long rest-frame time lags. (2) The ensemble SFs of BLSy1 galaxies, NLSy1 galaxies, and the combined sample are negatively correlated with the 5100 Å luminosity. The single power-law slope of the ensemble SF is proportional to luminosity. (3) The ensemble SFs of BLSy1 galaxies, NLSy1 galaxies, and the combined sample are negatively correlated with the Eddington ratio and the intensity of the Fe ii emission line. The MIR variability of the combined sample is positively correlated with black hole mass and the FWHM of the H β emission line at long rest-frame time lags. (4) The long-term MIR variability of the combined sample may be mainly driven by the Eddington ratio. (5) For BLSy1 galaxies, the MIR variability of radio-detected sources is greater than that of radio-undetected sources, whereas for NLSy1 galaxies, the opposite is true.