A multi-colour study of the dark GRB 000210 host galaxy and its environment

We present UBVRIZJs HKs broad band photometry of the host galaxy of the dark gamma-ray burst (GRB) of February 10, 2000. These observations represent the most exhaustive photometry given to date of any GRB host galaxy. A grid of spectral templates have been fitted to the Spectral Energy Distribution (SED) of the host. The derived photometric redshift is z=0.842+0.054-0.042, which is in excellent agreement with the spectroscopic redshift ( $z=0.8463\pm 0.0002$) proposed by Piro et al. (2002) based on a single emission line. Furthermore, we have determined the photometric redshift of all the galaxies in an area of $6^{\prime} \times 6^{\prime}$ around the host galaxy, in order to check for their overdensity in the environment of the host. We find that the GRB 000210 host galaxy is a subluminous galaxy ( $L \sim 0.5 \pm 0.2 \ L^{\star}$ ), with no companions above our detection threshold of $0.18 \pm 0.06 \ L^{\star}$. Based on the restframe ultraviolet flux a star formation rate of $2.1 \pm 0.2 \ M_{\odot}$ yr -1 is estimated. The best fit to the SED is obtained for a starburst template with an age of 0.181+0.037-0.026 Gyr and a very low extinction ( $A_{\rm V} \sim 0$). We discuss the implications of the inferred low value of $A_{\rm V}$ and the age of the dominant stellar population for the non-detection of the GRB 000210 optical afterglow.