SIMBAD references

We present the results of optical observations of the GRB 990510 field carried out at different epochs from European Southern Observatory (ESO) telescopes. Deep observations, down to a limiting magnitude of about 27 and 24 in the Bessel-R and Gunn-I band, respectively, were obtained between May 16 and 18 from the ESO NTT-SUSI2 telescope and on May 20 from the ESO 3.6m (EFOSC2) telescope. These observations, together with other published photometric data, allowed to monitor the faint tail of the decaying Optical Transient (OT) associated to the GRB 990510. We discuss the light curves in the different filters (V, R and I) in the light of the recently proposed decay laws. No obvious host associated to the GRB 990510 optical afterglow was found in the R and I band images. By comparing the light curves with respect to the theoretical colors of galaxies with different morphology we derived a lower limit of R∼26.6 for the host galaxy.