Neutron-fed afterglows of gamma-ray bursts

A neutron component is practically inevitable in baryonic fireballs of gamma-ray bursts (GRBs). At late stages of the explosion, the neutrons fully decouple from the ion ejecta and coast freely. The presence of the neutron ejecta qualitatively changes the mechanism of the GRB afterglow. The neutrons lead the decelerating blast wave and gradually decay, leaving behind a trail of the decay products mixed with the ambient medium. The kinetic energy of the decay products far exceeds the medium rest energy, and the trail has a Lorentz factor γ 1 at radii up to 10 cm. The ion ejecta decelerate behind as they sweep up the neutron trail and drive a shock wave into it. The afterglow is emitted by the preshock and postshock parts of the neutron trail. The neutron-fed afterglow can re-brighten at an observed time of tens of days. Subject headings: Cosmology: miscellaneous — gamma-rays: bursts — radiation mechanisms: nonthermal — shock waves