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 ≃ 1.5 absorbed by a column density NH > 5 × 1022 cm-2. The X-ray luminosity associated with the non-thermal components is ∼5 × 1041 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 rate onto the black hole.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science