Internal shocks at the origin of the flat spectral energy distribution of compact jets

TL;DR

This paper presents an internal shock model explaining the flat radio to IR spectrum of compact jets in X-ray binaries, showing how velocity fluctuations produce energy dissipation that balances adiabatic losses.

Contribution

It introduces a novel internal shock model with flicker noise velocity fluctuations to explain the flat spectrum of compact jets.

Findings

Shock dissipation balances adiabatic losses at large distances

Velocity fluctuations follow a 1/f power spectrum

Model reproduces observed flat radio to IR spectrum

Abstract

An internal shock model is proposed to interpret the radio to infrared (IR) emission of the compact jets observed in the hard spectral state of X-ray binaries. Assuming that the specific bulk Lorentz factor of the jet at its base varies with a flicker noise power spectrum (i.e. P(f)~1/f), I estimate the energy dissipation profile along the jet and the resulting partially self-absorbed synchrotron emission. For this type of velocity fluctuations, and a conical jet geometry, the shock dissipation at large distance from the black hole balances exactly the adiabatic losses. This leads to a flat radio to IR spectral energy distribution similar to that observed in compact jets.