Jet spectra in FR I radio galaxies: implications for particle acceleration

TL;DR

This paper presents high-precision radio spectral index imaging of FR I galaxy jets, revealing correlations between spectral properties, X-ray emission, and particle acceleration processes, with implications for jet deceleration and shear effects.

Contribution

It provides detailed spectral index measurements of FR I jets, linking spectral features to particle acceleration and jet dynamics, which advances understanding of jet physics.

Findings

Spectral index ~0.62 at jet brightening regions

X-ray emission correlates with specific spectral indices

Spectral flattening occurs where jet deceleration is modeled

Abstract

We describe very accurate imaging of radio spectral index for the inner jets in three FR I radio galaxies. Where the jets first brighten, there is a remarkably small dispersion around a spectral index of 0.62. This is also the region where bright X-ray emission is detected. Further from the nucleus, the spectral index flattens slightly to 0.50 - 0.55 and X-ray emission, although still detectable, is fainter relative to the radio. The brightest X-ray emission from the jets is therefore not associated with the flattest radio spectra, but rather with some particle-acceleration process whose characteristic energy index is 2.24. The change in spectral index occurs roughly where our relativistic jet models require rapid deceleration. Flatter-spectrum edges can be seen where the jets are isolated from significant surrounding diffuse emission and we suggest that these are associated with shear.