Observation of Centaurus A by theRossi X‐Ray Timing Explorer

Abstract

The Rossi X-Ray Timing Explorer made a short (10 ks) observation of the radio galaxy Centaurus A on 1996 August 14. Analysis of the combined 2.5-240 keV spectrum has revealed a heavily absorbed (NH=9.42±0.24×1022 cm-2) primary power law (Γ=1.86±0.015) and an iron line due to fluorescence of cold matter (EW=162±25 eV). Flux from a jet, a primary flux scattered into the line of sight, or a primary flux seen through a partial absorber was not required. The iron-line width is unresolved at the 95% confidence level (σ<0.54 keV). No significant variability in the iron-line flux is seen from measurements over the last two decades, while the overall continuum flux varied by more than a factor of 4, which implies that the line emission region is distant from that of the primary emission. While radio-quiet Seyfert galaxies exhibit spectral components attributable to Compton reflection from cold matter, Cen A reveals no such component (exposed solid angle ratio Ω/2π≤0.09). This supports unified models of active galaxies that have little difference between Seyfert 2 and low-luminosity radio galaxies.