Long-term Continuous Energy Injection in the Afterglow of GRB 060729

A long plateau phase and an amazing brightness have been observed in the Xray afterglow of GRB 060729. This peculiar light curve is likely due to long-term energy injection in external shock. Here we present a detailed numerical study on the energy injection process of magnetic dipole radiation from a strongly magnetized millisecond pulsar and model the multi-band afterglow observations. It is found that this model can successfully explain the long plateaus in the observed X-ray and optical afterglow light curves. The sharp break following the plateaus should be due to the rapid decline of the emission power of the central pulsar. At an even late time (~5*10^6s), an obvious jet break appears, which implies a relatively large half opening angle of theta~0.3 for the GRB ejecta. Due to the energy injection, the Lorentz factor of the outflow is still larger than two 10^7s post the GRB trigger, making the X-ray afterglow of this burst detectable by Chandra even 642 days after the burst.