Mid-infrared Variability of gamma-ray emitting blazars
  Using data from the Wide-field Infrared Survey Explorer we studied the mid
infrared 3.4 $\mu$m (W1-band) and 4.6 $\mu$m (W2-band) flux variability of
$\gamma$-ray emitting blazars. Our sample consists of 460 flat spectrum radio
quasars (FSRQs) and 575 BL Lacertae (BL Lac) objects. On intra-day timescales,
the median amplitude of variability ($\sigma_{m}$) for FSRQs is
0.04$^{+0.03}_{-0.02}$ mag and 0.05$^{+0.03}_{-0.02}$ mag in W1 and W2 bands.
For BL Lacs we found median $\sigma_{m}$ in W1(W2) bands of
0.04$^{+0.01}_{-0.02}$ (0.04$^{+0.02}_{-0.02}$) mag. On long timescales, for
FSRQs we found a median $\sigma_{m}$ of 0.44$^{+0.28}_{-0.27}$ mag and
0.45$^{+0.27}_{-0.27}$ mag in W1 and W2 bands, while for BL Lacs the median
values are 0.21$^{+0.18}_{-0.12}$ mag and 0.22$^{+0.18}_{-0.11}$ mag in W1 and
W2 bands. From statistical tests, we found FSRQs to show larger $\sigma_m$ than
BL Lacs on both intra-day and long timescales. Among blazars, low synchrotron
peaked (LSP) sources showed larger $\sigma_m$ compared to intermediate
synchrotron peaked (ISP) and high synchrotron peaked (HSP) sources.The larger
$\sigma_{m}$ seen in FSRQs relative to BL Lacs on both intra-day and long
timescales could be due to them having the most powerful relativistic jets
and/or their mid infrared 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
$\sigma_{m}$. In both FSRQs and BL Lacs predominantly a bluer when brighter
behaviour was observed. No correlation is found between $\sigma_m$ and black
hole mass.
