Comptonization model for Prompt optical and infrared emission of GRB 041219A

Prompt optical emission from the γ-ray burst of GRB 041219A has been reported by Vestrand et al. (2005). The facts that the fast rise of optical emission simultaneous with the dominant γ-ray pulse, and a tight correlation with the prompt γ-ray emission have been displayed. These indicate that the prompt optical emission and γ-ray emission would naturally have a common origin. We then propose that this optical component could be modelled by considering the Comptonization of γ-ray photons by an electron cloud. As a result of this mechanism, the arrival time of the optical photons is delayed comparing with that of the γ-rays. We restrict that the lagging time is shorter than 10 s, within which the prompt optical emission is considered as varying simultaneously with the prompt γ-ray emission. Taking into account of the observations of GRB 041219A, we derive the number density of the surrounding electron cloud required by Comptonization. The red-shift of GRB 041219A is predicted as z . 0.073 as well. Subject headings: γ-rays: bursts-radiation mechanisms: nonthermal