http://arxiv.org/abs/1310.5441
We explore the signature imprinted by dynamically relevant magnetic fields on the spectral energy distribution (SED) of blazars. It is assumed that the emission from these sources originates from the collision of ultrarelativistic and magnetized shells of cold plasma. A suitable analytic modeling, based on the numerical solution of Riemann problems, accounts for the magnetohydrodynamic evolution of the shell collisions. Using this dynamics we compute model SEDs including the most relevant radiative processes (synchrotron emission, synchrotron self-Compton and external inverse Compton scattering). To quantify the way in which the degree of magnetization shapes the SED, we scan a broad parameter space that encompasses a significant fraction of the commonly accepted values of not directly measurable physical properties. Starting from unmagnetized shell collisions, we reproduce the standard double hump SED found in blazar observations. We also show that the prototype double hump structure of blazars can also be reproduced if the dynamical source of the radiation field is very ultrarelativistic both, in a kinematically sense (namely, if it has Lorentz factors $\gtrsim 50$) and regarding its magnetization (e.g., with flow magnetizations $\sigma \simeq 0.1$). We find that a fair fraction of the {\em blazar sequence} could be explained in terms of the intrinsically different magnetization of the colliding shells: negligible magnetic fields might be present in FSRQs, while more moderate or large (and uniform) magnetization could explain the observed properties of BL Lacs. Our models, due to the approximated treatment of the Klein-Nishina cutoff, predict photon spectral indices ($\Gamma_{\rm ph}$) in the $\gamma-$ray band above the observed values if the magnetization of the sources is moderate ($\sigma\simeq 10^{-2}$).
Date added: Tue, 22 Oct 13