0 The collapsar model provides a very good model for the energetics, prompt gamma-ray emission, and the subsequent afterglow emission of long-duration GRBs. However, it does not provide a ready explanation for the apparent variations in the opening angle of the jet and in the explosive energy release. It has been speculated that there exist classes of relativistic explosions which have a lower Lorentz factor and wider opening angle than classical GRBs that peak in the X-ray band, known as dirty fireballs, with afterglows similar to classical GRBs. A decade- long search with ground-based optical surveys has found a dozen afterglows without a gamma-ray trigger, but their physical interpretation have been limited by a lack of coverage by high-energy missions, as well as a dearth of late-time sensitive afterglow observations. The recently launched Einstein Probe (EP) and Space Variable Objects Monitor (SVOM) are changing this landscape, offering a clear path to identify dirty fireballs. Here, we propose a comprehensive program with the VLA, XMM-Newton, and HST to help distinguish dirty fireballs from their primary false positives, GRBs viewed slightly off-axis. The discovery of a single dirty fireball would have a dramatic impact on our view of the GRB phenomenon. Stellar Physics and Stellar Types 6 false false false false false false false true SECONDARY NRAO VLA/26B-013 false SUPPORTED WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F606W