The relativistic iron line profile in the Seyfert 1 galaxy IC 4329A

We present simultaneous ASCA and RXTE data on the bright Seyfert 1 galaxy IC 4329A. The iron line is significantly broadened, but not to the extent expected from an accretion disk that extends down to the last stable orbit around a black hole. We marginally detect a narrow-line component, presumably from the molecular torus, but even including this gives a line profile from the accretion disk that is significantly narrower than that seen in MCG - 6-30-15, and is much more like that seen from the low/hard-state galactic black hole candidates. This is consistent with the inner disk being truncated before the last stable orbit, forming a hot flow at small radii, as in the advection-dominated accretion how (ADAF) models. However, we cannot rule out the presence of an inner disk that does not contribute to the reflected spectrum, either because of extreme ionization suppressing the characteristic atomic features of the reflected spectrum or because the X-ray source is intrinsically anisotropic, so it does not illuminate the inner disk. The source was monitored by RXTE every 2 days for 2 months, and these snapshot spectra show that there is intrinsic spectral variability. The data are good enough to disentangle the power law from the reflected continuum, and we see that the power law softens as the source brightens. The lack of a corresponding increase in the observed reflected spectrum implies that either the changes in disk inner radial extent and/or ionization structure are small, or that the variability is actually driven by changes in the seed photons that are decoupled from the hard X-ray mechanism.