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

摘要

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 Γ approx = 1.5 absorbed by a column density N_H > 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 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 rat onto the black hole.