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

R. Thimmappa, Ł. Stawarz, U. Pajdosz-Śmierciak, K. Balasubramaniam, V. Marchenko

Published 2021-03-22Version 1

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 {\it 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--7\,keV 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 three tens of kiloparsecs (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.