The host galaxy of GRB 031203: A new spectroscopic study

Aims. The host galaxy of the long-duration gamma-ray burst (GRB) 031203 (HG031203) offers a precious opportunity to study in detail the environment of a nearby GRB. The aim is to better characterize this galaxy and analyse the possible evolution with time of the spectroscopic quantities we derive. Methods. We analyse HG 031203 using a set of optical spectra acquired with the ESO-VLT and Keck telescope. We compare the metallicity, luminosity and star formation properties of this galaxy and of the other supernova-long gamma-ray burst hosts in the local universe (z < 0.2) against the KPNO International Spectroscopic Survey. Results. HG 031203 is a metal poor, actively star forming galaxy (star formation rate of 12.9 ± 2.2M_⊙ yr^-1) at z = 0.1054. From the emission-line analysis we derive an intrinsic reddening E _HG(B - V) ≈ 0.4. This parameter doesn't show a compelling evidence of evolution at a month time-scale. We find an interstellar medium temperature of ≈12 500 K and an electronic density of N_e = 160 cm ^-3. After investigating for possible Wolf-Rayet emission features in our spectra, we consider dubious the classification of HG 031203 as a Wolf-Rayet galaxy. Long gamma-ray burst (LGRB) and supernova hosts in the local universe (z < 0.2) show, on average, specific star formation rates higher than ordinary star forming galaxy at the same redshift. On the other hand, we find that half of the hosts follows the metallicity-luminosity relation found for star-burst galaxies; HG031203 is a clear outlier, with its really low metallicity (12 + log(0/H) = 8.12 ± 0.04).