2019MNRAS.488.4487C

The detailed modelling of the spectra observed from the long GRB031203 host galaxy at different epochs during the 2003-2009 yr is presented. The line profiles show FWHM of ∼100 km s^–1. A broad-line profile with FWHM <= 400 km s^–1 appears in the line sockets from the 2009 observations. We suggest that the narrow lines show the velocity of starburst (SB) debris, while the broad ones are due to the wind from SB stars. The spectra are emitted from the gas downstream of different shock fronts which are at work on the edges of the emitting clouds. A head-on-back shock appears when the wind from the SB stars reaches the internal edge of the SB debris moving outwards. A head-on shock is created by collision of the debris with the ISM clouds. Line ratios in both cases are calculated by the coupled effect of shock and photoionization from the SB. The models selected by fitting the calculated to the observed line ratios show that the ionization parameters, the shock velocities and the gas pre-shock densities slowly decrease with time. Oxygen metallicities (12+log(O/H) = 8.3-8.48) are lower than solar (8.82) by a factor <3 and nitrogen metallicities are lower than solar (12 + log(N/H) = 8.0, Grevesse & Sauval) by factors of 3-5.