A semi‐analytic model for cyclotron line formation

We present a semi‐analytic, physical motivated model for the formation of the cyclotron fundamental feature, in addition to the higher harmonic features, in static media of moderate depth. The spectra derived from the semi‐analytic model agree well with those obtained from ‘exact’ Monte Carlo simulations. These models are able to produce narrow fundamental and second harmonic features with comparable equivalent widths, which are the main characteristics of the harmonically spaced low energy absorption‐like features observed by the Ginga satellite in the spectra of three classical γ‐ray bursts. We are currently generalizing the semi‐analytic model to dynamic media, in particular, to line formation in a relativistic, radiation driven wind.