RXTE observations of 3C 273 between 1996 and 2000: Variability time-scale and jet power

We present the results of a long-look monitoring of 3C 273 with RXTE between 1996 and 2000. A total of 230 observations amounts to a net exposure of 845 ks, with this spectral and variability analysis of 3C 273 covering the longest observation period available at hard X-ray energies. Flux variations by a factor of 4 have been detected over 4 yr, whereas flux variations of less than 30 per cent have been observed for individual flares on time-scales of ∼3 d. Two temporal methods, the power spectrum density (PSD) and the structure function (SF), have been used to study the variability characteristics of 3C 273. The hard X-ray photon spectra generally show a power-law shape with a differential photon index of Γ ≃ 1.6 ± 0.1. In 10 of 261 data segments, exceptions to power-law behaviour have been found: (i) an additional soft excess below 4 keV; and (ii) a broad Fe fluorescent line feature with EW ∼ 100-200 eV. Our new observations of these previously reported X-ray features may imply that 3C 273 is a unique object whose hard X-ray emission occasionally contains a component that is not related to a beamed emission (Seyfert-like), but most hard X-rays are likely to originate in inverse Compton radiation from the relativistic jet (blazar-like). Multifrequency spectra from radio to γ-rays are presented in addition to our RXTE results. The X-ray time variability and spectral evolution are discussed in the framework of the beamed, synchrotron self-Compton picture. We consider the 'power balance' (both radiative and kinetic) between the accretion disc, the sub-parsec-scale jet and the 10-kpc-scale jet.