The Near Infrared and Multiwavelength Afterglow of GRB 000301c

We present near-infrared observations of the proposed counterpart of GRB 000301c. The K’ filter (2.1μm) light curve shows a well-sampled break in the decay slope at t ≈ 3.5 days post-burst. The early time slope is very shallow (∼ −0.1), while the late time slope is steep (−2.2). Comparison with the optical (R band) light curve shows significant differences, especially in the early time decay slope (which is steeper in the optical) and the break time (which occurs later in the optical). This is contrary to the general expectation that light curve breaks should either be achromatic (e.g., for breaks due to collimation effects) or should occur later at longer wavelengths (for most other breaks). We discuss some speculative explanations for this behavior. However, it is unclear if any of these can produce the observed contrast in behavior over a factor of only three in wavelength. In addition, by combining the IR-optical-UV data with millimeter and radio fluxes, we are able to constrain the locations of the self-absorption break and cooling break and to infer the location of the spectral peak, fν ≈ 2.3mJy at ν ≈ 5× 1011Hz. Subject headings: Gamma rays— bursts