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

Abstract

We present UBVRIZJsHKs 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 = 0.842-0.042+0.054, which is in excellent agreement with the spectroscopic redshift (z = 0.8463 ± 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′ × 6′ 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 ∼ 0.5 ± 0.2 L*), with no companions above our detection threshold of 0.18 ± 0.06 L*. Based on the restframe ultraviolet flux a star formation rate of 2.1 ± 0.2 M⊙ yr-1 is estimated. The best fit to the SED is obtained for a starburst template with an age of 0.181-0.026+0.037 Gyr and a very low extinction (Av ∼ 0). We discuss the implications of the inferred low value of Av and the age of the dominant stellar population for the non-detection of the GRB 000210 optical afterglow.