Orphan γ-ray flares from relativistic blobs encountering luminous stars

Abstract

We propose that γ-rays in blazars can be produced during encounters of relativistic blobs of plasma with radiation field produced by luminous stars within (or close to) the jet. The blob is expected to contain relativistic electrons which Comptonize stellar radiation to the GeV-TeV energies. Produced γ-rays can initiate the inverse Compton e± pair cascade in the stellar radiation. We propose that such a scenario can be responsible for the appearance of the so-called orphan γ-ray flares. We show that the relativistic blob/luminous star collision model can explain the appearance of the extreme orphan γ-ray flare observed in the GeV and sub-TeV energy range from the flat-spectrum radio quasar PKS 1222+21.