On the inability of comptonization to produce the broad X-ray iron lines observed in Seyfert nuclei

It has recently been suggested that Compton downscattering may give rise to the broad iron lines seen in the X-ray spectra of Seyfert 1 galaxies. This challenges the standard model, in which these lines originate from the inn ermost regions of the black hole accretion disk with Doppler shifts and gra vitational redshifts giving rise to the broadened line profile. Here we app ly observational constraints to the Compton downscattering model for MCG-6- 30-15 and NCC 3516, the two best cases to date of Seyfert galaxies with rel ativistically broad lines. We show that the continuum source in MCG-6-30-15 required by the constrained model violates the blackbody limit. In the cas e of NGC 3516, only a very small region of parameter space is compatible wi th the constraints. Hence, we conclude that the Comptonization model is not a viable one for the broad line seen in these two objects. The accretion d isk model remains the best interpretation of these data.