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

¹ Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, PR China
e-mail: lisl@shao.ac.cn
² University of Chinese Academy of Sciences, 19A Yuquan Road, 100049 Beijing, PR China

Received: 13 May 2021
Accepted: 26 July 2021

Abstract

Aims. 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 AGNs (such as the optical to X-ray spectral index α_OX and Eddington ration λ_O as well as the X-ray photon index Γ and λ_O) are not detected in RLAGNs. We intend to further investigate this issue in this work.

Methods. 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.

Results. It is found for the first time that there is a significant relationship between the mid-infrared to X-ray spectral index α_IX and λ_IR for whole sample, while there is no relationship between α_OX and λ_O in quasars. There are strong positive relationships between both L_R − L_X and L_UV − L_X panels, which can be well fitted by the disk-corona model. However, there is no significant relationship between Γ and λ_IR. The possible reason is related to the effects of the large-scale magnetic field in RLAGNs.

Conclusions. We suggest that the X-ray emission in high-excitation RLAGNs originates from a disk-corona system.