ar X iv : a st ro - p h / 02 07 00 9 v 1 2 9 Ju n 20 02 Time - Dependent Optical Spectroscopy of GRB 010222 : Clues to the GRB Environment 1

We present sequential optical spectra of the afterglow of GRB 010222 obtained one day apart using the Low Resolution Imaging Spectrometer (LRIS) and the Echellette Spectrograph and Imager (ESI) on the Keck telescopes. Three lowionization absorption systems are spectroscopically identified at z1 = 1.47688, z2 = 1.15628, and z3 = 0.92747. The higher resolution ESI spectrum reveals two distinct components in the highest redshift system at z1a = 1.47590 and z1b = 1.47688. We interpret the z1b = 1.47688 system as an absorption feature of the disk of the host galaxy of GRB 010222. The best fitted power-law optical continuum and [Zn/Cr] ratio imply low dust content or a local gray dust component near the burst site. In addition, we do not detect strong signatures of vibrationally excited states of H2. If the GRB took place in a superbubble or young stellar cluster, there are no outstanding signatures of an ionized absorber, either. Analysis of the spectral time dependence at low resolution shows no significant evidence for absorption-line variability. This lack of variability is confronted with time-dependent photoionization simulations designed to apply the observed flux from GRB 010222 to a variety of assumed atomic gas densities and cloud radii. The absence of time dependence in the absorption lines implies that high-density environments are disfavored. In particular, if the GRB environment was dust Based on data obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible with the generous financial support of the W.M. Keck Foundation Astronomy Department, Columbia University, 550 West 120th Street, New York, NY 10027 California Institute of Technology, Palomar Observatory 105-24, Pasadena, CA 91125 Infrared Processing and Analysis Center, 100-22 California Institute of Technology, 105-24, Pasadena, CA 91125 Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 National Radio Astronomy Observatory, Socorro, NM 87801