A new fundamental plane for radiatively efficient black-hole sources

TL;DR

This paper identifies a new fundamental plane linking radio and X-ray luminosities with black hole mass for radiatively efficient sources like bright AGNs and XRB 'outliers', revealing a unified accretion-jet relationship.

Contribution

It introduces a new fundamental plane specific to radiatively efficient black hole sources, expanding understanding of their accretion and jet physics.

Findings

Bright AGNs and XRB 'outliers' share similar Eddington ratio correlations.

A new fundamental plane for radiatively efficient sources is proposed.

The plane has a scatter of 0.51 dex, indicating good predictive power.

Abstract

In recent years, it was found that there are several low/hard state of X-ray binaries (XRBs) follow an `outliers' track of radio--X-ray correlation ($L_{\rm R}\propto L_{\rm X}^{b}$ and $b\sim1.4$), which is much steeper than the former universal track with $b\sim0.6$. In this work, we compile a sample of bright radio-quiet active galactic nuclei (AGNs) and find that their hard X-ray photon indices and Eddington ratios are positively correlated, which is similar to that of `outliers' of XRBs, where both bright AGNs and `outliers' of XRBs have bolometric Eddington ratios $\gtrsim1%L_{\rm Edd}$ ($L_{\rm Edd}$ is Eddington luminosity). The Eddington-scaled radio--X-ray correlation of these AGNs is also similar to that of `outliers' of XRBs, which has a form of $L_{\rm 5 GHz}/L_{\rm Edd}\propto (L_{\rm 2-10 keV}/L_{\rm Edd})^{c}$ with $c\simeq1.59$ and 1.53 for AGNs and XRBs respectively. Both the positively correlated X-ray spectral evolution and the steeper radio--X-ray correlation can be regulated by a radiatively efficient accretion flow (e.g., disk-corona). Based on these similarities, we further present a new fundamental plane for `outliers' of XRBs and bright AGNs in black-hole (BH) mass, radio and X-ray luminosity space: $\log L_{\rm R}=1.59^{+0.28}_{-0.22} \log L_{\rm X}- 0.22^{+0.19}_{-0.20}\log M_{\rm BH}-28.97^{+0.45}_{-0.45}$ with a scatter of $\sigma_{\rm R}=0.51\rm dex$. This fundamental plane is suitable for radiatively efficient BH sources, while the former plane proposed by Merloni et al. and Falcke et al. may be most suitable for radiatively inefficient sources.