Kiloparsec-scale jets in FR I radio galaxies and the γ-ray background

We discuss the contribution of kiloparsec- scale jets in FR I radio galaxies to the diffuse gamma- ray background radiation. The analyzed gamma- ray emission comes from inverse- Compton scattering of starlight photon fields by the ultrarelativistic electrons whose synchrotron radiation is detected from such sources at radio, optical, and X- ray energies. We find that these objects, under the minimum- power hypothesis ( corresponding to a magnetic field of 300 mu G in the brightest knots of these jets), can contribute about one percent to the extragalactic gamma- ray background measured by EGRET. We point out that this result already indicates that the magnetic fields in kiloparsec- scale jets of low- power radio galaxies are not likely to be smaller than 10 mu G on average, as otherwise the extragalactic gamma- ray background would be overproduced.