Equipartition Gamma-Ray Blazars and the Location of the Gamma-Ray Emission Site in 3C 279

TL;DR

This paper models the gamma-ray emission site in blazar 3C 279 using modified leptonic jet models with equipartition assumptions, deriving physical parameters and localizing the emission region near the outer BLR, while discussing hadronic contributions.

Contribution

It introduces a simplified analytical approach to constrain blazar jet parameters and localize gamma-ray emission sites, improving upon standard models with equipartition and external radiation field considerations.

Findings

Gamma-ray emission site is near the outer BLR (~0.1 pc).

Derived jet parameters: delta ~ 20-30, B' ~ few G.

Excess >5 GeV gamma-ray emission suggests possible hadronic origin.

Abstract

Blazar spectral models generally have numerous unconstrained parameters, leading to ambiguous values for physical properties like Doppler factor delta 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 delta, B', and the principal electron Lorentz factor gamma'_pk. The external radiation field in a blazar is approximated by Ly alpha radiation from the broad line region (BLR) and ~0.1 eV infrared radiation from a dusty torus. When used to model 3C 279 SEDs from 2008 and 2009 reported by Hayashida et al. (2012), we derive delta ~ 20-30, B' ~ few G, and total (IR + BLR) external radiation field energy densities u ~ 0.01 - 0.001 erg/cm^3, implying an origin of the gamma-ray emission site in 3C 279 at the outer edges of the BLR. This is consistent with the gamma-ray emission site being located at a distance R <~ Gamma^2 c t_{var} ~ 0.1 (\Gamma/30)^2 (t_{var}/10^4 s) pc from the black hole powering 3C 279's jets, where t_{var} is the variability time scale of the radiation in the source frame, and at farther distances for narrow-jet and magnetic_reconnection models. Excess >~ 5 GeV gamma-ray emission observed with Fermi LAT from 3C 279 challenge the model, opening the possibility of hadronic origins of the emission. For low hadronic content, absolute jet powers of ~10% of the Eddington luminosity are calculated.