SIMBAD references

We compute in detail the absorption optical depth for astrophysical γ-ray photons interacting with solar photons to produce electron-positron pairs. This effect is greatest for γ-ray sources at small angular distances from the Sun, reaching optical depths as high as τ_γγ ∼ 10^–2. We also calculate this effect including modifications to the absorption cross-section threshold from subluminal Lorentz invariance violation (LIV). We show for the first time that subluminal LIV can lead to increases or decreases in τ_γγ compared to the non-LIV case. We show that, at least in principle, LIV can be probed with this effect with observations of γ-ray sources near the Sun at ≳20 TeV by HAWC or LHAASO, although a measurement will be extremely difficult due to the small size of the effect.