The Afterglow of GRB 010222: A Case of Continuous Energy Injection

The optical light curve of GRB 010222 exhibited one of the slowest decays of any gamma-ray burst to date. Its broadband properties have been difficult to explain with conventional afterglow models, as they require either the power-law index of the underlying electron energy distribution to be low, p < 2, or the outflow to be quasi-spherical, thus reviving the energy problem. We argue that the slow decay of GRB 010222 and a linear polarization of 1.36% ± 0.64% are naturally explained by a jet model with continuous energy injection. The electron energy distribution then has p = 2.49 ± 0.05, fully consistent with the expectation from detailed modeling of acceleration in relativistic shocks that p > 2, thus alleviating the "p-problem."