Dimming of supernovae and gamma ray busts by Compton Scattering and its   cosmological implications
  Free electrons deplete photons from type Ia supernovae through the (inverse) Compton scattering. This Compton dimming increases with redshift and reaches 0.004 mag at $z=1$ and 0.01 mag at $z=2$. Although far from sufficient to invalidate the existence of dark energy, it can bias constraint on dark energy at a level non-negligible for future supernova surveys. This effect is correctable and should be incorporated in supernova analysis. The Compton dimming has similar impact on cosmology based on gamma ray bursts as standard candles. 
Pengjie Zhang (SHAO)