The radio source 3C 264 , hosted by the giant elliptical galaxy NGC 3862 , was observed with VERITAS between February 2017 and May 2019 .
These deep observations resulted in the discovery of very-high-energy ( VHE ; E > 100 GeV ) \gamma -ray emission from this active galaxy .
An analysis of \sim 57 hours of quality-selected live time yields a detection at the position of the source , corresponding to a statistical significance of 7.8 standard deviations above background .
The observed VHE flux is variable on monthly time scales , with an elevated flux seen in 2018 observations .
The VHE emission during this elevated state is well-characterized by a power-law spectrum with a photon index \Gamma = 2.20 \pm 0.27 and flux F ( > 315 GeV ) = ( 7.6 \pm 1.2 _ { \mathrm { s } tat } \pm 2.3 _ { \mathrm { s } yst } ) \times 10 ^ { -13 } cm ^ { -2 } s ^ { -1 } , or approximately 0.7 % of the Crab Nebula flux above the same threshold .
3C 264 ( z = 0.0217 ) is the most distant radio galaxy detected at VHE , and the elevated state is thought to be similar to that of the famously outbursting jet in M 87 .
Consequently , extensive contemporaneous multi-wavelength data were acquired in 2018 at the time of the VHE high state .
An analysis of these data , including VLBA , VLA , HST , Chandra and Swift observations in addition to the VERITAS data , is presented , along with a discussion of the resulting spectral energy distribution .