Very-High-Energy Gamma Rays from a Distant Quasar: How Transparent Is the Universe?

The atmospheric Cherenkov gamma- ray telescope MAGIC, designed for a low- energy threshold, has detected very- high- energy gamma rays from a giant flare of the distant Quasi- Stellar Radio Source ( in short: radio quasar) 3C 279, at a distance of more than 5 billion light- years ( a redshift of 0.536). No quasar has been observed previously in very- high- energy gamma radiation, and this is also the most distant object detected emitting gamma rays above 50 gigaelectron volts. Because high- energy gamma rays may be stopped by interacting with the diffuse background light in the universe, the observations by MAGIC imply a low amount for such light, consistent with that known from galaxy counts.