The evolution of the large-scale emission in FRI jets

TL;DR

This paper models the evolution of emission from FRI jet termination regions, predicting spectra and lightcurves to aid in understanding particle acceleration and emission mechanisms over time.

Contribution

It introduces a coupled relativistic simulation and radiation model to predict the spectral and temporal evolution of thermal and non-thermal emission in FRI jets.

Findings

Synchrotron radiation dominates non-thermal emission under moderate magnetic fields.

X-ray emission is mainly from shocked jet synchrotron, with thermal components significant in older sources.

Inverse Compton scattering can produce detectable GeV and TeV fluxes, increasing with source age.

Abstract

Recent observations in X-rays and gamma-rays of nearby FRI radio galaxies have raised the question of the origin of the emission detected in the termination structures of their jets. The study of these structures can give information on the conditions for particle acceleration and radiation at the front shocks. In addition, an evolutionary scenario can help to disentangle the origin of the detected X-ray emission in young FRI sources, like some Gigahertz Peaked Spectrum AGNs. This work focuses on the nature and detectability of the radiation seen from the termination regions of evolving FRI jets. We use the results of a relativistic, two-dimensional numerical simulation of the propagation of an FRI jet, coupled with a radiation model, to make predictions for the spectra and lightcurves of the thermal and non-thermal emission at different stages of the FRI evolution. Our results show that under moderate magnetic fields, the synchrotron radiation would be the dominant non-thermal channel, appearing extended in radio and more compact in X-rays, with relatively small flux variations with time. The shocked jet synchrotron emission would dominate the X-ray band, although the shocked ISM/ICM thermal component alone may be significant in old sources. Inverse Compton scattering of CMB photons could yield significant fluxes in the GeV and TeV bands, with a non-negligible X-ray contribution. The IC radiation would present a bigger angular size in X-rays and GeV than in TeV, with fluxes increasing with time. We conclude that the thermal and non-thermal broadband emission from the termination regions of FRI jets could be detectable for sources located up to distances of a few 100 Mpc.