  If Lorentz violation exists, it will affect the thresholds for pair creation
processes. Lorentz-violating operators that change the maximum velocities of
charged particles may increase or decrease the extinction rate of gamma-rays
moving through space. If the emissions from high-energy astrophysical sources
do not show any signs of anomalous absorption, this allows us to place bounds
on the Lorentz-violating c coefficients for multiple species of charged
particles. The bounds for a species of mass m_X based on observing photons at
an energy E can be O(m_X^2/E^2), which corresponds to limits at the
10^(-15)(m_X^2/m_e^2) level for the most energetic photons.
