Exploring the Nature of Gamma-ray Burst Shallow Decay

Abstract

We have studied the optical temporal evolution of 42 Swift GRBs. Our investigation shows that most of the optical properties can be interpreted by the external shock model and implies that the observed optical emission originated from this model. However, of the 42 GRBs, 10 show shallow decay properties in their overall optical light curve. Further investigations into the 10 GRBs found that the corresponding shallow decay properties were also found in their X-ray light curve. Apart from GRB 050730, our results also indicate that most shallow decay orginates from the external shock in both X-ray and optical. We conclude that, for some bursts, the optical and X-ray shallow decay have an extrnal origin, but some bursts have different emission mechanisms.