Dissipation Efficiency of Reconfinement Shocks in Relativistic Jets

Abstract

We calculate the dissipation efficiency of relativistic reconfinement shocks. Building on previous work (Nalewajko & Sikora 2009), we consider different distributions of the external pressure. The average dissipation efficiency epsilon_diss is a function of the product of two parameters - the jet Lorentz factor Gamma_j and the reconfinement angle Theta_r, which is related to the opening angle Theta_j and the external pressure index eta. The spatial distribution of the dissipation rate strongly depends on eta. We discuss the significance of these results for the properties of relativistic jets in gamma-ray bursts and active galactic nuclei and propose that reconfinement shocks may explain a very high dissipation efficiency of the former and a moderate dissipation efficiency of the latter. Finally, we estimate the dissipation efficiency of the reconfinement shock associated with the quasi-stationary knot HST-1 in the jet of radio galaxy M87 and show that it is roughly consistent with the observational constraints.Comment: 5 pages, 4 figures, submitted to MNRAS Letter