Infrared variability of radio-loud narrow-line Seyfert 1 galaxies
  Most of the radio-loud narrow-line Seyfert 1 (NLS1) galaxies resemble compact
steep-spectrum sources. However, the extremely radio-loud ones show blazar-like
characteristics, like flat radio spectra, compact radio cores, substantial
variability and high brightness temperatures. These objects are thought to be
similar to blazars as they possess relativistic jets seen at small angle to the
line of sight. This claim has been further supported by the Fermi satellite
discovery of gamma-ray emission from a handful of these sources. Using the
Wide-Field Infrared Survey Explorer (WISE) data, we analyzed the mid-infrared
variability characteristics of $42$ radio-loud NLS1 at $3.4$ and $4.6\,\mu$m.
We found that $27$ out of the studied $42$ sources showed variability in at
least one of the two infrared bands. In some cases, significant changes in the
infrared colors can alter the location of the source in the WISE color-color
diagram which might lead to different classification. More than $60$% of the
variable sources also showed variability within a $1-1.5$ day interval. Such
short time scales argue for a compact emission region like those associated
with the jets. This connection is further strengthened by the fact that the
brightest $\gamma$-ray emitters of the sample ($6$ sources), all showed short
time scale infrared variability.
