  Studies of bibliographic data suggest a strong correlation between the growth
of citation networks and their corresponding co-authorship networks. We explore
the interdependence between evolving citation and co-authorship networks
focused on the publications, by Indian authors, in American Physical Society
journals between 1970 and 2013. We record interactions between each possible
pair of authors in two ways: first, by tracing the change in citations they
exchanged and, second, by tracing the shortest path between authors in the
co-authorship network. We create these data for every year of the period of our
analysis. We use probability methods to quantify the correlation between
citations and shortest paths, and the effect on the dynamics of the
citation-co-authorship system. We find that author pairs who have a
co-authorship distance $d \leq 3$ significantly affect each others citations,
but that this effect falls off rapidly for longer distances in the
co-authorship network. The exchange of citation between pairs with $d=1$
exhibits a sudden increase at the time of first co-authorship events and decays
thereafter, indicating an aging effect in collaboration. This suggests that the
dynamics of the co-authorship network appear to be driving those of the
citation network rather than vice versa. Moreover, the majority of citations
received by most authors are due to reciprocal citations from current, or past,
co-authors. We conclude that, in order to answer questions on nature and
dynamics of scientific collaboration, it is necessary to study both
co-authorship and citation network simultaneously.
