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 approximate to 1.5 absorbed by a column density N-H > 5 x 10(22) cm(-2). The X-ray luminosity associated with the non-thermal component is similar to5 x 10(41) erg s(-1). The nuclear source is embedded in a diffuse hot gas ( kT similar to 0.6- 0.65 keV), whose density profile implies a Bondi accretion rate of similar to4.5 x 10(-2) M-. 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.