RAPID INFRARED VARIABILITY OF THREE RADIO-LOUD NARROW-LINE SEYFERT 1 GALAXIES: A VIEW FROM THE WIDE-FIELD INFRARED SURVEY EXPLORER

Using newly released data from the Wide-field Infrared Survey Explorer, we report the discovery of rapid infrared variability in three radio-loud narrow-line Seyfert 1 galaxies (NLS1s) selected from the 23 sources in the sample of Yuan et al. J0849+5108 and J0948+0022 clearly show intraday variability, while J1505+0326 has a longer measurable timescale within 180 days. Their variability amplitudes, corrected for measurement errors, are ~0.1-0.2 mag. The detection of intraday variability restricts the size of the infrared-emitting region to ~10-3 pc, significantly smaller than the scale of the torus but consistent with the base of a jet. The three variable sources are exceptionally radio-loud, have the highest radio brightness temperature among the whole sample, and all show detected gamma -ray emission in Fermi/LAT observations. Their spectral energy distributions resemble those of low-energy-peaked blazars, with a synchrotron peak around infrared wavelengths. This result strongly confirms the view that at least some radio-loud NLS1s are blazars with a relativistic jet close to our line of sight. The beamed synchrotron emission from the jet contributes significantly to and probably dominates the spectra in the infrared and even optical bands.