Evidence of non-thermal X-ray emission from radio lobes of Cygnus A

TL;DR

This study provides evidence of non-thermal X-ray emission from Cygnus A's radio lobes, indicating inverse Compton processes involving CMB and synchrotron photons, with electron energy density dominating over magnetic energy.

Contribution

First detection of non-thermal X-ray emission from Cygnus A's radio lobes using deep Chandra data, revealing details of the inverse Compton process and energy densities.

Findings

Non-thermal X-ray emission detected from both lobes.

Inverse Compton process involving CMB and synchrotron photons confirmed.

Electron energy density exceeds magnetic energy density in the lobes.

Abstract

Using deep Chandra ACIS observation data for Cygnus A, we report evidence of non-thermal X-ray emission from radio lobes surrounded by a rich intra-cluster medium (ICM). The diffuse X-ray emission, which are associated with the eastern and western radio lobes, were observed in a 0.7--7 keV Chandra$ ACIS image. The lobe spectra are reproduced with not only a single-temperature Mekal model, such as that of the surrounding ICM component, but also an additional power-law (PL) model. The X-ray flux densities of PL components for the eastern and western lobes at 1 keV are derived as 77.7^{+28.9}_{-31.9} nJy and 52.4^{+42.9}_{-42.4} nJy, respectively, and the photon indices are 1.69^{+0.07}_{-0.13} and 1.84^{+2.90}_{-0.12}, respectively. The non-thermal component is considered to be produced via the inverse Compton (IC) process, as is often seen in the X-ray emission from radio lobes. From a re-analysis of radio observation data, the multiwavelength spectra strongly suggest that the seed photon source of the IC X-rays includes both cosmic microwave background radiation and synchrotron radiation from the lobes. The derived parameters indicate significant dominance of the electron energy density over the magnetic field energy density in the Cygnus A lobes under the rich ICM environment.