The origin of X-ray emission in 3CRR sources: hints from mid-infrared Spitzer observations

TL;DR

This study investigates the origin of X-ray emission in radio-loud AGNs, finding evidence that it likely originates from a disk-corona system, with new relationships identified between mid-infrared and X-ray properties.

Contribution

The paper provides new observational evidence linking mid-infrared and X-ray emissions, supporting the disk-corona origin of X-ray emission in high-excitation radio-loud AGNs.

Findings

Significant relationship between mid-infrared to X-ray spectral index and infrared luminosity.

Strong positive correlations between radio/X-ray and UV/X-ray luminosities.

No significant correlation between X-ray photon index and infrared luminosity.

Abstract

Whether X-ray emission in radio-loud (RL) active galactic nuclei (AGNs) originates from disk coronae or jets is still under debate. For example, the positive relationships in radio-quiet (RQ) AGNs (such as the optical to X-ray spectral index $\alpha_{\rm {OX}}$ and Eddington ration $\lambda_{\rm {O}}$ as well as the X-ray photon index $\Gamma$ and $\lambda_{\rm {O}}$) are not detected in RLAGNs. We intend to further investigate this issue in this work. A sample of 27 luminous sources (including 16 quasars and 11 high-excitation radio galaxies) was selected from the 3CRR catalog to reinvestigate the origin of X-ray emission in RLAGNs, where the X-ray and mid-infrared fluxes are observed by Chandra/XMM-Newton and Spitzer, respectively. It is found for the first time that there is a significant relationship between the mid-infrared to X-ray spectral index $\alpha_{\rm {IX}}$ and $\lambda_{\rm {IR}}$ for whole sample, while there is no relationship between $\alpha_{\rm {OX}}$ and $\lambda_{\rm {O}}$ in quasars. There are strong positive relationships between both $L_{\rm {R}}$-$L_{\rm {X}}$ and $L_{\rm {UV}}$-$L_{\rm {X}}$ panels, which can be well fitted by the disk-corona model. However, there is no significant relationship between $\Gamma$ and $\lambda_{\rm {IR}}$. The possible reason is related to the effects of the large-scale magnetic field in RLAGNs. We suggest that the X-ray emission in high-excitation RLAGNs originates from a disk-corona system.