Synchrotron and inverse-Compton emission from blazar jets - II. An accelerating jet model with a geometry set by observations of M87

TL;DR

This paper develops a detailed accelerating jet model based on M87 observations to explain multi-wavelength emissions from blazars, fitting data well and suggesting similar jet geometries across different sources.

Contribution

The study extends the Potter & Cotter (2012) jet model by incorporating a magnetically dominated accelerating base with geometry set by M87, and applies it to a blazar, fitting observations effectively.

Findings

Jet remains magnetically dominated within the BLR.

Best fit occurs when jet reaches equipartition outside the BLR.

Jet geometry of PKS0227 similar to scaled M87 model.

Abstract

In this paper we develop the jet model of Potter & Cotter (2012) to include a magnetically dominated accelerating parabolic base transitioning to a slowly decelerating conical jet with a geometry set by recent radio observations of M87. We conserve relativistic energy-momentum and particle number along the jet and calculate the observed synchrotron emission from the jet by calculating the integrated line of sight synchrotron opacity through the jet in the rest frame of each section of plasma. We calculate the inverse-Compton emission from synchrotron, CMB, accretion disc, starlight, broad line region, dusty torus and narrow line region photons by transforming into the rest frame of the plasma along the jet. We fit our model to simultaneous multi-wavelength observations of the Compton-dominant FSRQ type blazar PKS0227-369, with a jet geometry set by M87 and an accelerating bulk Lorentz factor consistent with simulations and theory. We investigate models in which the jet comes into equipartition at different distances along the jet and equipartition is maintained via the conversion of jet bulk kinetic energy into particle acceleration. We find that the jet must still be magnetically dominated within the BLR and cannot be in equipartition due to the severe radiative energy losses. The model fits the observations, including radio data, very well if the jet comes into equipartition outside the BLR within the dusty torus (1.5pc) or at further distances (34pc). We find that our fit in which the jet comes into equipartition furthest along the jet, which has a jet with the geometry of M87 scaled linearly with black hole mass, has an inferred black hole mass close to previous estimates. This implies that the jet of PKS0227 might be well described by the same jet geometry as M87.