At z = 0.1055, the gamma-ray burst GRB 031203 is one of the two nearest GRBs known. Using observations from the Very Large Array (VLA) and Chandra X-ray Observatory we derive sub-arcsecond localizations of the radio and X-ray afterglow of this GRB. We present near-infrared observations of the supernova SN 2003lw, which exploded in the host galaxy of the GRB 031203. Our deep, high resolution Magellan/PANIC data establish that this SN is spatially coincident with the radio and X-ray localizations

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... of the afterglow of GRB 031203 to subarcsecond precision, and is thus firmly associated with the GRB. We use image differencing to subtract the bright emission from the host galaxy, and measure the time evolution of the SN between ∼ 5 and ∼ 50 days after the GRB. The resulting light curve has a shape which is quite different from that of the two SNe previously associated with GRBs, SN 1998bw and SN 2003dh. With SN 11 The possible classification of this event as an X-ray flash (XRF) was debated in recent literature (e.g., Prochaska et al. 2004; Watson et al. 2004; Thomsen et al. 2004 ). However, the high-energy observations presented by Sazonov, Lutovinov, & Sunyaev (2004) conclusively show that this event does not fit any of the commonly used definitions of XRFs.