Delayed GEV Emission from Cosmological Gamma-Ray Bursts - Impact of a Relativistic Wind on External Matter

Sudden collapse of a compact object, or coalescence of a compact binary, can generate an unsteady relativistic wind that lasts for a few seconds. The wind is likely to carry a high magnetic field; and its Lorentz factqr depends on the extent to which it is `loaded' with baryons. If the Lorentz factor is 100, internal dissipation and shocks in this wind produce a non-thermal gamma-ray burst, detectable in the range 0.1 MeV< Ey <0.1-1 GeV out to cosmological distances. The cooled wind ejecta will subsequently be decelerated by the external medium. The resultant blast wave and reverse shock can then give rise to a second burst component, mainly detectable in the GeV range, with a time delay relative to the MeV burst ranging from minutes to hours. Key words: MHD - relativity - shock waves - gamma-rays: bursts.