  In this paper we apply the reverberation method to determine the mass of the
black hole in 3C273 from the Ly a and C iv emission lines using archival IUE
observations. Following the standard assumptions of the method, we find a
maximum-likelihood estimate of the mass of 6.59 10^9 Mo, with a 1 sigma
confidence interval 5.69-8.27 10^9 Mo. This estimate is more than one order of
magnitude larger than that obtained in a previous study using Balmer lines. We
reanalyze the optical data and show that the method applied to the Ha, Hb, and
Hg Balmer lines produce mass estimates lower by a factor 2.5, but already much
larger than the previous estimate derived from the same lines. The finding of
such a high mass in a face-on object is a strong indication that the gas motion
is not confined to the accretion disk. The new mass estimate makes 3C273
accreting with an accretion rate about six times lower than the Eddington rate.
We discuss the implications of our result for the broad-line-region size and
black-hole mass vs luminosity relationships for the set of objects for which
reverberation black-hole masses have been obtained. We find that, while objects
with super-Eddington luminosities might theoretically be possible, their
existence is not necessarily implied by this sample.
