The non-thermal emission of extended radio galaxy lobes with curved electron spectra

TL;DR

This paper develops a new framework to characterize the curved electron spectra in radio galaxy lobes, enabling direct calculation of physical properties and predicting inverse-Compton X-ray emission without assuming cutoff frequencies.

Contribution

It introduces a novel method to analyze curved electron spectra using observable parameters, improving estimates of magnetic fields and energies in radio galaxy lobes.

Findings

Provides a way to determine Lorentz factors at spectral turnover.

Enables calculation of equipartition magnetic field strength and total plasma energy.

Predicts inverse-Compton X-ray emission from radio lobes.

Abstract

The existing theoretical framework for the energies stored in the synchrotron-emitting lobes of radio galaxies and quasars doesn't properly account for the curved spectral shape that many of them exhibit. We characterise these spectra using parameters that are straightforwardly observable in the era of high-resolution, low-frequency radio astronomy: the spectral curvature and the turnover in the frequency spectrum. This characterisation gives the Lorentz factor at the turnover in the energy distribution (we point out that this is distinctly different from the Lorentz factor corresponding to the turnover frequency in a way that depends on the amount of curvature in the spectrum) and readily gives the equipartition magnetic field strength and the total energy of the radiating plasma obviating the need for any assumed values of the cutoff frequencies to calculate these important physical quantities. This framework readily yields the form of the X-ray emission due to inverse-Compton (IC) scattering of Cosmic Microwave Background (CMB) photons by the electrons in the plasma having Lorentz factors of $\sim$1000. We also present the contribution to CMB anisotropies due to relativistic plasmas such as giant radio galaxy lobes, expressed in terms of the extent to which the lobes have their magnetic field and particle energies are in equipartition with one another.