Analysis of hard two-photon correlations measured in heavy-ion reactions at intermediate energies

Recently reported measurements of hard photon correlations in the reactions $^{36}\mathrm{Ar}$ on $^{27}\mathrm{Al}$ at $95A$ MeV, $^{86}\mathrm{Kr}$ on $^{\mathrm{nat}}\mathrm{Ni}$ at $60A$ MeV, and $^{181}\mathrm{Ta}$ on $^{197}\mathrm{Au}$ at $39.5A$ MeV are analyzed. A Boltzmann-\"Uhling-Uhlenbeck transport model is used to describe the photon production by individual nucleon-nucleon collisions. In the lighter systems we find the best agreement with data when taking into account only photons from first-chance collisions of nucleons or photons produced during the passage of the nuclei, while the model predicts also a considerable late-time emission of photons, which leads to a depletion of the calculated correlation function. The accuracy of the present data does not allow firm conclusions on the reliability of this late-time evolution. Our investigations do not support a recently reported interference pattern in the heavy Ta + Au system.