Rapid Infrared Variability of Three Radio-loud Narrow-line Seyfert 1 Galaxies: A View from the Wide-field Infrared Survey Explorer

摘要

Using newly released data from the Wide-field Infrared Survey Explorer, wereport the discovery of rapid infrared variability in three radio-loudnarrow-line Seyfert 1 galaxies (NLS1s) selected from the 23 sources in thesample of Yuan et al. (2008). J0849+5108 and J0948+0022 clearly show intradayvariability, while J1505+0326 has a longer measurable time scale within 180days. Their variability amplitudes, corrected for measurement errors, are $\sim0.1-0.2$ mag. The detection of intraday variability restricts the size of theinfrared-emitting region to $\sim 10^{-3}$ pc, significantly smaller than thescale of the torus but consistent with the base of a jet. The three variablesources are exceptionally radio-loud, have the highest radio brightnesstemperature among the whole sample, and all show detected $\gamma$-ray emissionin Fermi/LAT observations. Their spectral energy distributions resemble thoseof low-energy-peaked blazars, with a synchrotron peak around infraredwavelengths. This result strongly confirms the view that at least someradio-loud NLS1s are blazars with a relativistic jet close to our line ofsight. The beamed synchrotron emission from the jet contributes significantlyto and probably dominates the spectra in the infrared and even optical bands.