2016MNRAS.459..508B

GRB 141221A was observed from infrared to soft gamma-ray bands. Here, we investigate its properties, in light of the standard model. We find that the optical light curve of the afterglow of this burst presents an unusual steep/quick rise. The broad-band spectral energy distribution taken near the maximum of the optical emission presents either a thermal component or a spectral break. In the former case, the properties of the afterglow are then very unusual, but could explain the lack of apparent jet breaks in the Swift light curves. In the latter case, the afterglow properties of this burst are more usual, and we can see in the light curves the passing through of the injection and cooling frequencies within the optical bands, not masked by a reverse shock. This model also excludes the presence of a stellar wind, challenging either the stellar progenitor properties, or the very stellar nature of the progenitor itself. In all cases, this burst may be a part of a Rosetta stone that could help to explain some of the most striking features discovered by Swift during the last 10 years.