Elliptic flow of thermal photons and formation time of quark gluon plasma at energies available at the BNL Relativistic Heavy Ion Collider (RHIC)

We calculate the elliptic flow of thermal photons from Au+Au collisions at RHIC energies for a range of values for the formation time tau(0) but a fixed entropy (or particle rapidity density). The results are found to be quite sensitive to tau(0). The value of v(2) for photons decreases as tau(0) decreases and admits a larger contribution from the quark gluon plasma phase, which has a smaller v(2). The elliptic flow coefficient for hadrons, however, is only marginally dependent on tau(0).