The early optical afterglow and non-thermal components of GRB 060218

Abstract

We re-examine the UV/optical and X-ray observations of GRB 060218 during the prompt and afterglow phases. We present evidence in the UV/optical spectra that there is a synchrotron component contributing to the observed flux in the initial 1350 s. This result suggests that GRB 060218 is produced from a low-luminosity jet, which penetrates through its progenitor envelope after core collapse. The jet interacts with the surrounding medium to generate the UV/optical external shock synchrotron emission. After 1350 s, the thermal radiation in the UV/optical and X-ray becomes the dominant contribution to the observed flux. The UV/optical and X-ray spectra at 1350-10 000 s can be fitted with a spherically outflowing blackbody model, with an additional power-law component to the model at X-ray energies.