VLT observations of GRB 990510 and its environment
K. Beuermann, F.V. Hessman, K. Reinsch, H. Nicklas, P.M. Vreeswijk, T.J. Galama, E. Rol, J. van Paradijs, C. Kouveliotou, F. Frontera, N. Masetti, E. Palazzi, E. Pian
Abstract
We present BVRI photometry and spectrophotometry of GRB990510 obtained with the ESO VLT/Antu telescope during the late decline phase. Between days 8 and 29 after the burst, the afterglow faded from R=24.2 to ~26.4. The spectral flux distribution and the light curve support the interpretation of the afterglow as synchrotron emission from a jet. The light curve is consistent with the optical transient alone but an underlying SN with maximum brightness R>27.4 or a galaxy with R>27.6 (3-sigma upper limits) cannot be ruled out. To a 5-sigma detection threshold of R=26.1, no galaxy is found within 6'' of the transient. A very blue V~24.5 extended object which may qualify as a starburst galaxy is located 12'' SE, but at unknown redshift.