Azimuthal asymmetry of direct photons in intermediate energy heavy-ion collisions

Hard photon emitted from energetic heavy ion collisions is of very interesting since it does not experience the late-stage nuclear interaction, therefore it is useful to explore the early-stage information of matter phase. In this work, we have presented a first calculation of azimuthal asymmetry, characterized by directed transverse flow parameter F and elliptic asymmetry coefficient v2, for proton-neutron bremsstrahlung hard photons in intermediate energy heavy-ion collisions. The positive F and negative v2 of direct photons are illustrated and they seem to be anti-correlated to the corresponding free proton's flow.