  Pion-kaon correlation functions are constructed from central Au+Au data taken
at $\sqrt{s_{NN}} = 130$ GeV. The results suggest that pions and kaons are not
emitted at the same average space-time point. Space-momentum correlations, i.e.
transverse flow, lead to a space-time emission asymmetry of pions and kaons
that is consistent with the data. This result provides new independent evidence
that the system created at RHIC undergoes a collective transverse expansion.
