The Long-term Infrared Brightness and Color Variabilities of γ-ray-loud Narrow-line Seyfert 1 Galaxies

The detection of GeV γ-rays from some narrow-line Seyfert 1 galaxies (γ-ray-loud NLS1s) has received increasing attention. Up to now, 22 γ-ray-loud NLS1s and other 3 high-confidence candidates has been reported. Using the data platform of Wide-field Infrared Survey Explorer (WISE), we derived the simultaneous photometric data in the W₁ (3.4 μm) and W₂ (4.6 μm) bands (from January 2010 to December 2019) for these sources. Then we analyzed their long-term variability via the parameter V and the normalized excess variance σ_NXV² methods. It was found that 24 sources showed long-term brightness (W₁ magnitude) variabilities, and 17 sources showed long-term color (W₁-W₂) variabilities. When studying the correlation between color and magnitude, we found that 7 sources showed a redder-when-brighter (RWB) trend, and 4 sources showed a trend of bluer-when-brighter (BWB). Finally, the possible causes of color changes and implication are briefly discussed.