XMM-Newton Observations of the Nuclei of the Radio Galaxies 3C 305, DA 240, and 4C 73.08

TL;DR

This study uses XMM-Newton observations to analyze the nuclear X-ray emissions of three radio galaxies, revealing different emission mechanisms and challenging some existing classifications of narrow-line radio galaxies.

Contribution

First detailed X-ray spectral analysis of these specific radio galaxy nuclei, highlighting diversity in emission origins and questioning traditional classification boundaries.

Findings

4C 73.08 shows combined absorbed and unabsorbed X-ray components.

DA 240's X-ray emission is dominated by jet-related unabsorbed power law.

3C 305 lacks expected heavily absorbed X-ray emission, suggesting a different nuclear environment.

Abstract

We present new XMM-Newton EPIC observations of the nuclei of the nearby radio galaxies 3C 305, DA 240, and 4C 73.08, and investigate the origin of their nuclear X-ray emission. The nuclei of the three sources appear to have different relative contributions of accretion- and jet-related X-ray emission, as expected based on earlier work. The X-ray spectrum of the FRII narrow-line radio galaxy (NLRG) 4C 73.08 is modeled with the sum of a heavily absorbed power law that we interpret to be associated with a luminous accretion disk and circumnuclear obscuring structure, and an unabsorbed power law that originates in an unresolved jet. This behavior is consistent with other narrow-line radio galaxies. The X-ray emission of the low-excitation FRII radio galaxy DA 240 is best modeled as an unabsorbed power law that we associate with a parsec-scale jet, similar to other low-excitation sources that we have studied previously. However, the X-ray nucleus of the narrow-line radio galaxy 3C 305 shows no evidence for the heavily absorbed X-ray emission that has been found in other NLRGs. It is possible that the nuclear optical spectrum in 3C 305 is intrinsically weak-lined, with the strong emission arising from extended regions that indicate the presence of jet--environment interactions. Our observations of 3C 305 suggest that this source is more closely related to other weak-lined radio galaxies. This ambiguity could extend to other sources currently classified as NLRGs. We also present XMM-Newton and VLA observations of the hotspot of DA 240, arguing that this is another detection of X-ray synchrotron emission from a low-luminosity hotspot.