On the injection of relativistic electrons in the jet of 3C 279

Abstract

ABSTRACT The acceleration of electrons in 3C 279 is investigated through analysing the injected electron energy distribution (EED) in a time-dependent synchrotron self-Compton+external Compton emission model. In this model, it is assumed that relativistic electrons are continuously injected into the emission region, and the injected EED [$Q_{\rm e}^\prime (\gamma ^\prime)$] follows a single power-law form with low- and high-energy cut-offs $\rm \gamma _{min}^{\prime }$ and $\rm \gamma _{max}^{\prime }$, respectively, and the spectral index n, i.e. $Q_{\rm e}^\prime (\gamma ^\prime)\propto \gamma ^{\prime -n}$. This model is applied to 14 quasi-simultaneous spectral energy distributions of 3C 279. The Markov Chain Monte Carlo (MCMC)-fitting technique is performed to obtain the best-fitting parameters and the uncertainties on the parameters. The results show that the injected EED is well constrained in each state. The value of n is in the range of 2.5–3.8, which is larger than that expected by the classic non-relativistic shock acceleration. However, the large value of n can be explained by the relativistic oblique shock acceleration. The flaring activity seems to be related to an increased acceleration efficiency, reflected in an increased $\gamma ^{\prime }_{\rm min}$ and electron injection power.