TeV gamma rays from 3C 279 - A possible probe of origin and intergalactic infrared radiation fields

Abstract

The γ-ray spectrum of 3C 279 during 1991 June exhibited a near perfect power law between 50 MeV and over 5 GeV with a differential spectral index of -(2.02 +/- 0.07). If extrapolated, the γ-ray spectrum of 3C 279 should be easily detectable with first generation air Cerenkov detectors operating above ~ 0.3 TeV, provided there is no intergalactic absorption. However, by using model-dependent lower and upper limits for the extragalactic infrared background radiation field, we predict a sharp cutoff of the 3C 279 spectrum between ~0.1 and ~1 TeV. The sensitivity of present air Cerenkov detectors is good enough to measure such a cutoff, which would provide the first opportunity to obtain a measurement of, or at least a severe constraint on the extragalactic background infrared radiation field.