Attenuation of TeV $\gamma$-rays by the starlight photon field of the
  host galaxy
  The absorption of TeV $\gamma$-ray photons produced in relativistic jets by
surrounding soft photon fields is a long-standing problem of jet physics. In
some cases the most likely emission site close to the central black hole is
ruled out because of the high opacity caused by strong optical and infrared
photon sources, such as the broad line region. Mostly neglected for jet
modeling is the absorption of $\gamma$-rays in the starlight photon field of
the host galaxy. Analyzing the absorption for arbitrary locations and
observation angles of the $\gamma$-ray emission site within the host galaxy we
find that the distance to the galaxy center, the observation angle, and the
distribution of starlight in the galaxy are crucial for the amount of
absorption. We derive the absorption value for a sample of $20$ TeV detected
blazars with a redshift $z_r<0.2$. The absorption value of the $\gamma$-ray
emission located in the galaxy center may be as high as $20\%$ with an average
value of $6\%$. This is important in order to determine the intrinsic blazar
parameters. We see no significant trends in our sample between the degree of
absorption and host properties, such as starlight emissivity, galactic size,
half-light radius, and redshift. While the uncertainty of the spectral
properties of the extragalactic background light exceeds the effect of
absorption by stellar light from the host galaxy in distant objects, the latter
is a dominant effect in nearby sources. It may also be revealed in a
differential comparison of sources with similar redshifts.
