A Structured Leptonic Jet Model of the “Orphan” TeV Gamma‐Ray Flares in TeV Blazars

Abstract

The emission spectra of TeV blazars extend up to tens of TeV, and the emission mechanism of the TeV γ-rays is explained by synchrotron self-Compton scattering in leptonic models. In these models the time variabilities of X-rays and TeV γ-rays are correlated. However, recent observations of 1ES 1959+65.0 and Mrk 421 have found the TeV γ-ray flares, i.e., TeV γ-ray flares without simultaneous X-ray flares. In this paper we propose a model for the orphan TeV γ-ray flares, employing an inhomogeneous leptonic jet model. After a primary flare that accompanies flare-up both in X-rays and TeV γ-rays, radiation propagates in various directions in the comoving frame of the jet. When a dense region in the jet receives the radiation, X-rays are scattered by relativistic electrons/positrons to become TeV γ-rays. These γ-ray photons are observed as an orphan TeV γ-ray flare. The observed delay time between the primary and orphan flares is about 2 weeks, and this is accounted for in our model for parameters such as Γ = 20, d = 4 × 1017 cm, α = 3, and η = 1, where Γ is the bulk Lorentz factor of the jet, d is the distance between the central black hole and the primary flare site, α/Γ is the angle between the jet axis and the direction of the motion of the dense region that scatters incoming X-rays produced by the primary flare, and η/Γ is the angle between the jet axis and the line of sight.