The spectral energy distribution of compact jets powered by internal shocks

Abstract

Internal shocks caused by fluctuations of the outflow velocity are likely to\npower the radio to IR emission of the compact jets of X-ray binaries. The\ndynamics of internal shocks and the resulting spectral energy distribution\n(SED) of the jet are very sensitive to the time-scales and amplitudes of the\nvelocity fluctuations injected at the base of the jet. I present a new code\ndesigned to simulate the synchrotron emission of a compact jet powered by\ninternal shocks. I also develop a semi-analytical formalism allowing one to\nestimate the observed SED of the jet as a function of the Power Spectral\nDensity (PSD) of the assumed fluctuations of the Lorentz factor. I discuss the\ncases of a sine modulation of the Lorentz factor and Lorentz factor\nfluctuations with a power-law PSD shape. Independently of the details of the\nmodel, the observed nearly flat SEDs are obtained for PSDs of Lorentz factor\nfluctuations that are close to a flicker noise spectrum (i.e. P(f)~1/f). The\nmodel also presents a strong wavelength dependent variability that is similar\nto that observed in these sources.\n