We present spectra of the optical transient (OT) associated with GRB 021004. The spectra show a blue continuum with superposed absorption features and one emission line. There are two intervening metal-line systems at z = 1.380 and z = 1.602 and one very strong absorption system at a redshift of z = 2.323. Lyα emission is also seen at this redshift. While the spectrum of the OT overall cannot be simply described with a power law, the spectral index over the range 5500 − 8850 ˚A is steep, Fν ∝ ν −0.96±0.03. Comparison of spectra from multiple epochs shows a distinct color evolution with the OT becoming redder with time, implying a B − V increase of ∼ 0.2 − 0.3 mag over the first three days. This is the first clear example of color change in an OT detected spectroscopically. Subject headings: galaxies: distances and redshifts—galaxies: ISM—gamma rays: bursts—ultraviolet: galaxies
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