Mid-infrared variability of the neutrino source blazar TXS 0506$+$056
  The IceCube instrument detected a high-energy cosmic neutrino event on 2017
September 22 (IceCube_170922A, IceCube Collaboration 2018), which the
electromagnetic follow-up campaigns associated with the flaring $\gamma$-ray
blazar TXS 0506$+$056 (e.g., Padovani et al., 2018). We investigated the
mid-infrared variability of the source by using the available single exposure
data of the WISE satellite at $3.4$ and $4.6\mu$m. TXS 0506$+$056 experienced a
$\sim 30$% brightening in both of these bands a few days prior to the neutrino
event. Additional intraday infrared variability can be detected in 2010.
Similar behaviour seen previously in $\gamma$-ray bright radio-loud AGN has
been explained by their jet emission (e.g., Jiang et al. 2012).
