2020MNRAS.494..764A

Using data from the Wide-field Infrared Survey Explorer, we studied the mid-infrared (mid-IR) 3.4 µm (W1-band) and 4.6 µm (W2-band) flux variability of γ-ray emitting blazars. Our sample consists of 460 flat spectrum radio quasars (FSRQs) and 575 BL Lacertae (BL Lac) objects. On intraday time-scales, the median amplitude of variability (σ_m) for FSRQs is 0.04^+0.03_–0.02 and 0.05^+0.03_–0.02 mag in W1 and W2 bands. For BL Lacs, we found median σ_m in W1(W2) bands of 0.04^+0.01_–0.02 (0.04^+0.02_–0.02) mag. On long time-scales, for FSRQs we found a median σ_m of 0.44^+0.28_–0.27 and 0.45^+0.27_–0.27 mag in W1 and W2 bands, while for BL Lacs, the median values are 0.21^+0.18_–0.12 and 0.22^+0.18_–0.11 mag in W1 and W2 bands. From statistical tests, we found FSRQs to show larger σ_m than BL Lacs on both intraday and long time-scales. Among blazars, low synchrotron peaked sources showed larger σ_m compared to intermediate synchrotron peaked and high synchrotron peaked sources. The larger σ_m seen in FSRQs relative to BL Lacs on both intraday and long time-scales could be due to them having the most powerful relativistic jets and/or their mid-IR band coinciding with the peak of the electron energy distribution. BL Lacs have low power jets and the observational window too traces the emission from low-energy electrons, thereby leading to low σ_m. In both FSRQs and BL Lacs predominantly a bluer when brighter behaviour was observed. No correlation is found between σ_m and black hole mass.