  We propose a model for an evolving citation network that incorporates the
citation pattern followed in a particular discipline. We define the citation
pattern in a discipline by three factors. The average number of references per
article, the probability of citing an article based on its age and the number
of citations it already has. We also consider the average number of articles
published per year in the discipline. We propose that the probability of citing
an article based on its age can be modeled by a lifetime distribution. The
lifetime distribution models the citation lifetime of an average article in a
particular discipline. We find that the citation lifetime distribution in a
particular discipline predicts the topological structure of the citation
network in that discipline. We show that the power law exponent depends on the
three factors that define the citation pattern. Finally we fit the data from
the Physical Review D journal to obtain the citation pattern and calculate the
total degree distribution for the citation network.
