Testing the External Shock Model of Gamma-Ray Bursts using the Late-Time Simultaneous Optical and X-ray Afterglows

Yuji Urata, Ryo Yamazaki, Takanori Sakamoto +21

We study the ``normal'' decay phase of the X-ray afterglows of gamma-ray bursts (GRBs), which follows the shallow decay phase, using the events simultaneously observed in the R-ban…