NEAR-EQUIPARTITION JETS with LOG-PARABOLA ELECTRON ENERGY DISTRIBUTION and the BLAZAR SPECTRAL-INDEX DIAGRAMS

Abstract

Fermi-LAT analyses show that the γ-ray photon spectral indices of a large sample of blazars correlate with the peak synchrotron frequency according to the relation . The same function, with different constants d and k, also describes the relationship between and peak Compton frequency . This behavior is derived analytically using an equipartition blazar model with a log-parabola description of the electron energy distribution (EED). In the Thomson regime, for external Compton (EC) processes and for synchrotron self-Compton (SSC) processes, where b is the log-parabola width parameter of the EED. The BL Lac object Mrk 501 is fit with a synchrotron/SSC model given by the log-parabola EED, and is best fit away from equipartition. Corrections are made to the spectral-index diagrams for a low-energy power-law EED and departures from equipartition, as constrained by absolute jet power. Analytic expressions are compared with numerical values derived from self-Compton and EC scattered γ-ray spectra from Ly broad-line region and IR target photons. The versus behavior in the model depends strongly on b, with progressively and predictably weaker dependences on γ-ray detection range, variability time, and isotropic γ-ray luminosity. Implications for blazar unification and blazars as ultra-high energy cosmic-ray sources are discussed. Arguments by Ghisellini et al. that the jet power exceeds the accretion luminosity depend on the doubtful assumption that we are viewing at the Doppler angle.