Probing a Gamma-Ray Burst Progenitor at a Redshift of<i>z</i>= 2: A Comprehensive Observing Campaign of the Afterglow of GRB 030226

Abstract

We report results from a comprehensive follow-up observing campaign of the\nafterglow of GRB 030226, including VLT spectroscopy, VLT polarimetry, and\nChandra X-ray observations. In addition, we present BOOTES-1 wide-field\nobservations at the time of the occurrence of the burst. First observations at\nESO started 0.2 days after the event when the GRB afterglow was at a magnitude\nof R~19 and continued until the afterglow had faded below the detection\nthreshold (R&gt;26). No underlying host galaxy was found. The optical light curve\nshows a break around 0.8 days after the burst, which is achromatic within the\nobservational errors, supporting the view that it was due to a jetted\nexplosion. Close to the break time the degree of linear polarization of the\nafterglow light was less than 1.1%, which favors a uniform jet model rather\nthan a structured one. VLT spectra show two absorption line systems at\nredshifts z=1.962+/-0.001 and at z=1.986+/-0.001, placing the lower limit for\nthe redshift of the GRB close to 2. We emphasize that the kinematics and the\ncomposition of the absorbing clouds responsible for these line systems is very\nsimilar to those observed in the afterglow of GRB 021004. This corroborates the\npicture in which at least some GRBs are physically related to the explosion of\na Wolf-Rayet star.\n