The Suzaku View of the Disk-Jet Connection in the Low Excitation Radio Galaxy NGC 6251

TL;DR

This study uses Suzaku X-ray observations to analyze NGC 6251, a low-excitation radio galaxy, confirming the absence of obscured accretion signatures and supporting the idea that such galaxies accrete inefficiently with energy mainly channeled into jets.

Contribution

The paper provides detailed X-ray spectral analysis of NGC 6251, supporting the hypothesis that low-excitation radio galaxies lack obscuring tori and have radiatively inefficient accretion.

Findings

No evidence of obscured, accretion-related X-ray emission.

X-ray luminosity is substantially below Eddington luminosity.

Spectral modeling confirms thermal emission from galaxy and group-scale plasma.

Abstract

We present results from an 87-ks Suzaku observation of the canonical low-excitation radio galaxy (LERG) NGC 6251. We have previously suggested that LERGs violate conventional AGN unification schemes: they may lack an obscuring torus and are likely to accrete in a radiatively inefficient manner, with almost all of the energy released by the accretion process being channeled into powerful jets. We model the 0.5-20 keV Suzaku spectrum with a single power law of photon index $\Gamma=1.82^{+0.04}_{-0.05}$, together with two collisionally ionized plasma models whose parameters are consistent with the known galaxy- and group-scale thermal emission. Our observations confirm that there are no signatures of obscured, accretion-related X-ray emission in NGC 6251, and we show that the luminosity of any such component must be substantially sub-Eddington in nature.