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In many GRBs, afterglows have been observed for months or even years. Itdeserves noting that at such late stages, the remnants should have entered thedeep Newtonian phase, during which the majority of shock-accelerated electronswill no longer be highly relativistic. However, a small portion of electronsare still ultra-relativistic and capable of emitting synchrotron radiation.Under the assumption that the electrons obey a power-law distribution accordingto their kinetic energy (not simply the Lorentz factor), we calculate opticalafterglows from both isotropic fireballs and beamed ejecta, paying specialattention to the late stages. In the beamed cases, it is found that the lightcurves are universally characterized by a flattening during the deep Newtonianphase. Implication of our results on orphan afterglows is also addressed.Comment: Shortened to 4 pages, to appear in the proceedings of the 2003 GRB  conference (Santa Fe, Sept 8 -- 12, 2003

GRB Afterglows in the Deep Newtonian Phase