Detecting and quantifying the relativistic Kelvin-Helmholtz instability in interstellar jets via radiation observable on Earth

We present a microscopic model of the radiation emitted during the relativistic Kelvin-Helmholtz instability (KHI) and validate our findings with particle-in-cell simulations at unprecedented spatial resolution and size that including complete far-field radiation spectra.

The KHI is expected in shear flow regions of astrophysical plasma jets, which are significant sites for particle acceleration and radiation. We demonstrate that the emitted polarized radiation can be used to identify and characterize the microscopic plasma dynamics of a KHI light-years away. We have simulated the radiation of the KHI using the particle-in-cell code PIConGPU. With this code's synthetic radiation diagnostic, based on Liénard-Wiechert potentials, quantitative predictions of the far field radiation for hundreds of observation directions and a frequency range covering 3 orders of magnitude were performed on the TITAN cluster at Oak Ridge National Laboratory. The simulation showed that the time-dependent changes in the radiation polarization and power correlate directly with the stages of the KHI. This allows identifying the linear growth phase of the KHI and quantifying its characteristic growth rate as predicted by our microscopic model.