The optical afterglow and host galaxy of GRB000926

J. U. Fynbo, J. Gorosabel, T. H. Dall, J. Hjorth, H. Pedersen, M. I. Andersen, P. Moller, I. Smail, N. Kobayashi, P. Vreeswijk, I. Burud, S. Holland, B. L. Jensen, B. Thomsen, A. Henden, F. Vrba, B. Canzian, J. M. Castro Cerón, A. J. Castro-Tirado, T. Cline, M. Goto, J. Greiner, M. T. Hanski, K. Hurley, N. Lund, T. Pursimo, R. Oestensen, J. Solheim, N. Tanvir, H. Terada

Published 2001-02-09, updated 2001-04-11Version 2

We present the discovery of the Optical Transient (OT) of the long-duration gamma-ray burst GRB000926. The optical transient was detected independently with the Nordic Optical Telescope and at Calar Alto 22.2 hours after the burst. At this time the magnitude of the transient was R = 19.36. The transient faded with a decay slope of about 1.7 during the first two days after which the slope increased abruptly (within a few hours) to about 2.4. The light-curve started to flatten off after about a week indicating the presence of an underlying extended object. This object was detected in a deep image obtained one month after the GRB at R=23.87+-0.15 and consists of several compact knots within about 5 arcsec. One of the knots is spatially coincident with the position of the OT and hence most likely belongs to the host galaxy. Higher resolution imaging is needed to resolve whether all the compact knots belong to the host galaxy or to several independent objects. In a separate paper we present a discussion of the optical spectrum of the OT, and its inferred redshift (Moller et al. in prep.).