2014ApJ...782...82D

Blazar spectral models generally have numerous unconstrained parameters, leading to ambiguous values for physical properties like Doppler factor δ_D or fluid magnetic field B'. To help remedy this problem, a few modifications of the standard leptonic blazar jet scenario are considered. First, a log-parabola function for the electron distribution is used. Second, analytic expressions relating energy loss and kinematics to blazar luminosity and variability, written in terms of equipartition parameters, imply δ_D, B', and the peak electron Lorentz factor γ'_pk. The external radiation field in a blazar is approximated by Lyα radiation from the broad-line region (BLR) and ~0.1 eV infrared radiation from a dusty torus. When used to model 3C 279 spectral energy distributions from 2008 and 2009 reported by Hayashida et al., we derive δ_D∼ 20-30, B' ∼ few G, and total (IR + BLR) external radiation field energy densities u ∼ 10^–2-10^–3 erg/cm3, implying an origin of the γ-ray emission site in 3C 279 at the outer edges of the BLR. This is consistent with the γ-ray emission site being located at a distance R ≲ Γ² ct_var∼ 0.1(Γ/30)²(t_var/10⁴ s) pc from the black hole powering 3C 279's jets, where t_var is the variability timescale of the radiation in the source frame, and at farther distances for narrow-jet and magnetic-reconnection models. Excess ≳ 5 GeV γ-ray emission observed with Fermi LAT from 3C 279 challenges the model, opening the possibility of a second leptonic component or a hadronic origin of the emission. For low hadronic content, absolute jet powers of ~10% of the Eddington luminosity are calculated.