Spitzer observations of SN 2014J and properties of mid-IR emission in
  Type Ia supernovae
  SN 2014J in M82 is the closest Type Ia supernova (SN Ia) in decades. The
proximity allows for detailed studies of supernova physics and provides
insights into the circumstellar and interstellar environment. In this work we
analyze Spitzer mid-IR data of SN 2014J in the 3.6 and 4.5 {\mu}m wavelength
range, together with several other nearby and well-studied SNe Ia. We compile
the first composite mid-IR light-curve templates from our sample of SNe~Ia,
spanning the range from before peak brightness well into the nebular phase. Our
observations indicate that SNe Ia form a very homogeneous class of objects at
these wavelengths. Using the low-reddening supernovae for comparison, we
constrain possible thermal emission from circumstellar dust around the highly
reddened SN 2014J. We also study SNe 2006X and 2007le, where the presence of
matter in the circumstellar environment has been suggested. No significant
mid-IR excess is detected, allowing us to place upper limits on the amount of
pre-existing dust in the circumstellar environment. For SN 2014J, $M_{dust} <
10^{-5}$ M$_{\odot}$ within $r_{dust} \sim 10^{17}$ cm, which is insufficient
to account for the observed extinction. Similar limits are obtained for SNe
2006X and 2007le.
