Photon production through $A_1$ resonance in high energy heavy ion collisions

Electromagnetic radiation from excited hadronic matter is one of the best ways to study the properties of the matter. Considering various processes in the hadronic gas, Kapusta et al \cite{Kapusta_photons} have found a $\pi\rho \rightarrow \pi\gamma$ reaction with intermediate virtual pion or rho to be the main source of photons with energy greater than 0.7 GeV. However, at temperatures considered T=100-200 MeV, a $\pi\rho$ pair can easily form an $A_1$(1260) resonance, and we show that this mechanism leads to the photon production rates exceeding those suggested previously. The paper is in LATEX, figures available from authors.