Giant Lobes of Centaurus A Radio Galaxy Observed with the Suzaku X-ray Satellite

TL;DR

This study uses Suzaku X-ray observations to analyze the giant lobes of Centaurus A, revealing localized electron acceleration and a possible thermal gas component, suggesting inhomogeneous lobe structures with ongoing magnetic reconnection.

Contribution

First detailed X-ray analysis of Centaurus A's giant lobes indicating localized electron acceleration and thermal gas presence, highlighting complex lobe inhomogeneity.

Findings

Synchrotron origin favored for X-ray features

Detection of a soft thermal excess at 0.5 keV

Thermal gas pressure in equipartition with non-thermal components

Abstract

[abridged] We report on Suzaku observations of selected regions within the Southern giant lobe of the radio galaxy Centaurus A. We focus on distinct X-ray features likely associated with fine radio structure of the lobe. We find that the spectral properties of the detected X-ray features are equally consistent with thermal emission from hot gas, or with a power-law radiation continuum. However, the plasma parameters implied by these different models favor a synchrotron origin for the analyzed X-ray spots, indicating that a very efficient acceleration of electrons is taking place within the giant structure of Centaurus A, albeit only in isolated and compact regions. We also present a detailed analysis of the diffuse X-ray emission, resulting in a tentative detection of a soft excess component best fitted by a thermal model with a temperature of 0.5 keV. The exact origin of the observed excess remains uncertain, although energetic considerations point to thermal gas filling the bulk of the volume of the lobe and mixed with the non-thermal plasma. The corresponding pressure of the thermal gas in such a case appears to be in almost exact equipartition with the pressure provided by the radio-emitting electrons and the magnetic field. Although tentative, our findings potentially imply that the structure of the extended lobes in active galaxies is likely to be highly inhomogeneous, with magnetic reconnection processes continuously converting magnetic energy to internal energy of the plasma particles, leading to spatial and temporal variations in the plasma parameters around the equilibrium condition.