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

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 αOX and Eddington ration λO as well as the X-ray photon index Γ and λO) 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 αIX and λIR for whole sample, while there is no relationship between αOX and λO in quasars. There are strong positive relationships between both LR − LX and LUV − LX panels, which can be well fitted by the disk-corona model. However, there is no significant relationship between Γ and λIR. 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.