Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: How gravitational lensing helps gamma-ray photons avoid $\gamma -
  \gamma$ absorption   We investigate potential $\gamma-\gamma$ absorption of gamma-ray emission
from blazars arising from inhomogeneities along the line of sight, beyond the
diffuse Extragalactic Background Light (EBL). As plausible sources of excess
$\gamma-\gamma$ opacity, we consider (1) foreground galaxies, including cases
in which this configuration leads to strong gravitational lensing, (2)
individual stars within these foreground galaxies, and (3) individual stars
within our own galaxy, which may act as lenses for microlensing events. We
found that intervening galaxies close to the line-of-sight are unlikely to lead
to significant excess $\gamma-\gamma$ absorption. This opens up the prospect of
detecting lensed gamma-ray blazars at energies above 10 GeV with their
gamma-ray spectra effectively only affected by the EBL. The most luminous stars
located either in intervening galaxy or in our galaxy provides an environment
in which these gamma-rays could, in principle, be significantly absorbed.
However, despite a large microlensing probability due to stars located in
intervening galaxies, gamma-rays avoid absorption by being deflected by the
gravitational potentials of such intervening stars to projected distances
("impact parameters"') where the resulting $\gamma-\gamma$ opacities are
negligible. Thus, neither of the intervening excess photon fields considered
here, provide a substantial source of excess $\gamma-\gamma$ opacity beyond the
EBL, even in the case of very close alignments between the background blazar
and a foreground star or galaxy.

9
The categories of this paper are: nlin
25
The categories of this paper are: patt-sol
37
The categories of this paper are: supr-con
17
The categories of this paper are: q-fin
27
The categories of this paper are: comp-gas
24
The categories of this paper are: dg-ga
36
The categories of this paper are: cmp-lg
8
The categories of this paper are: hep-ex
22
The categories of this paper are: chao-dyn
34
The categories of this paper are: chem-ph
5
The categories of this paper are: gr-qc
4
The categories of this paper are: cond-mat
16
The categories of this paper are: stat
28
The categories of this paper are: alg-geom
7
The categories of this paper are: hep-th
3
The categories of this paper are: physics