The origin of X-ray emission in Low-Excitation Radio Galaxies

In previous works, the radio-X-ray slope in FRI radio galaxies is found to be steeper compared with that in low-luminosity AGNs, indicating different origin of the X-ray emission. Here we reinvestigate this point by compiling a sample of 13 low-excitation radio galaxies (LERG) from 3CR radio catalog of galaxies, where the central engine in LERG is accepted to be a radiatively inefficient accretion flow (RIAF). The core radio and X-ray emissions in all the objects of our sample are detected by VLA/VLBI/VLBA and Chandra/XMM-Newton, respectively. Surprisingly, a shallower slope of L_R - L_x relation (?) is given by our sample, which demonstrates that the X-ray emission in LERG may come from accretion disk rather than a jet as suggested by previous works. In addition, the slope in the fundamental plane ((log L_R = 0.52 log L_X + 0.84 log M_BH + 10.84) of LERG is found to be well consistent with that reported by Merloni et al. (<xref rid="r6" ref-type="bibr">2003</xref>).