Elliptic flow of thermal photons at midrapidity in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV

The elliptic flow $v_2$ of thermal photons at midrapidity in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV is predicted, based on three-dimensional ideal hydrodynamics. Because of the interplay between the asymmetry and the strength of the transverse flow, the thermal photon $v_2$ reaches a maximum at $\text{pt}\sim$ 2GeV/$c$ and the $\text{pt}$-integrated $v_2$ reaches a maximum at about 50% centrality. The $\text{pt}$-integrated $v_2$ is very sensitive to the lower limit of the integral but not sensitive to the upper limit due to the rapid decrease in the spectrum of the transverse momentum.