On the origin of the X-rays and the nature of accretion in NGC 4261

We report on the X-ray properties of the radio galaxy NGC 4261 , combining information from the XMM-Newton, Chandra, and BeppoSAX satellites. Goals of this study are to investigate the origin of the X-rays from this low-power radio galaxy and the nature of the accretion process onto the central black hole. The X-ray spectrum of the nuclear source extending up to 100-150 keV is well described by a partially covered (covering factor >0.8) power law with a photon index (gamma)( asymptotically equal)1.5absorbed by a column density NH>5*10^22 cm^-2. The X-ray luminosity associated with the non-thermal component is ~5*10^41 erg s^-1. The nuclear source is embedded in a diffuse hot gas ( kT~0.6-0.65 keV), whose density profile implies a Bondi accretion rate of ~4.5*10^ -2 M(circled dot operator) yr^-1. For the first time rapid X-ray variability is detected in a low-power radio galaxy at more than 99% confidence level. The observed X-ray spectral and variability properties indicate the accretion flow as the most likely origin of the bulk X-ray continuum. This conclusion is strengthened by energetic considerations based on a comparison between the X-ray luminosity and the kinetic power of the jet, which also suggest that the Bondi accretion rate overestimates the actual accretion rate onto the black hole.