Complex Structure of the Eastern Lobe of the Pictor A Radio Galaxy: Spectral Analysis and X-ray/Radio Correlations

TL;DR

This study provides a detailed spectral and correlation analysis of X-ray and radio features in the Eastern lobe of Pictor A, revealing a new filament with unique properties and insights into the lobe's magnetic and thermal structure.

Contribution

It introduces the discovery of a bright X-ray filament upstream of the jet termination, analyzing its properties and correlations with radio emission for the first time.

Findings

Identification of a new X-ray filament extending 30 kpc

Anti-correlation between X-ray brightness and polarized radio intensity

Decrease in radio rotation measure near the filament

Abstract

Here we present detailed analysis of the distinct X-ray emission features present within the Eastern radio lobe of the Pictor A galaxy, around the jet termination region, utilising the data obtained from the Chandra X-ray Observatory. Various emission features have been selected for the study based on their enhanced X-ray surface brightness, including five sources that appear point-like, as well as three extended regions, one characterised by a filamentary morphology. For those, we perform a basic spectral analysis within the 0.5-7keV range. We also investigate various correlations between the X-ray emission features and the non-thermal radio emission, utilising the high-resolution radio maps from the Very Large Array at GHz frequencies. The main novel findings following from our analysis, regard the newly recognized bright X-ray filament located upstream of the jet termination region, extending for at least thirty kiloparsec (projected), and inclined with respect to the jet axis. For this feature, we observe a clear anti-correlation between the X-ray surface brightness and the polarized radio intensity, as well as a decrease in the radio rotation measure with respect to the surroundings. We speculate on the nature of the filament, in particular addressing a possibility that it is related to the presence of a hot X-ray emitting thermal gas, only partly mixed with the non-thermal radio/X-ray emitting electrons within the lobe, combined with the reversals in the lobe's net magnetic field.