Optical - Infrared ANDICAM Observations of the Transient Associated with GRB 030329

We present photometry of the transient associated with GRB 030329 obtained with the CTIO 1.3–meter telescope and the ANDICAM instrument, a dual optical/infrared imager with a dichroic centered at one micron. Without the need for light curve interpolation to produce snapshot broadband spectra, we show that the transient spectrum remained statistically achromatic from day 2.7 to day 5.6, during a re-brightening episode. Associating the light in these early epochs with the GRB afterglow, we infer a modest level of extinction due to the host galaxy in the line–of–sight toward the GRB: A V (host) = 0.30 ± 0.03 mag for β = −0.5 and A V (host) < 0.4 mag (3 σ) for any physically plausible value of β (with flux f ν ∝ ν β). We conclude that the spectral slope of the afterglow component was more than β = −0.8 between day 2.7–5.6 after the GRB, excluding the possibility that the synchrotron cooling break passed through the optical/IR bandpass over that period. Taking extinction into account, a decomposition of the light curve into an afterglow and supernova component requires the presence of a supernova similar to that of SN 1998bw, an afterglow that shows some evidence for a second break around day 8–10, and a fifth re-brightening event around day 15.