The elementary spike produced by a pure e(+)e(-) pair-electromagnetic pulse from a Black Hole: The PEM Pulse

In the framework of the model that uses black holes endowed with electromag netic. structure (EMBH) as the energy source, we study how an elementary sp ike appears to the detectors. We consider the simplest possible case of a p ulse produced by a pure e(+)e(-) pair-electro-magnetic plasma. the PEM puls e, in the absence of any baryonic matter. The resulting time profiles show a Fast-Rise-Exponential-Decay shape, followed by a power-law tail. This is obtained without any special fitting procedure, but only by fixing the ener getics of the process taking place in a given EMBH of selected mass, varyin g in the range from 10 to 10(3) M-circle dot and considering the relativist ic effects to be expected in an electron-positron plasma gradually reaching transparency. Special attention is given to the contributions from all reg imes with Lorentz gamma factor varying from gamma = 1 to gamma = 10(4) in a few hundreds of the PEM pulse travel time. Although the main goal of this paper is to obtain tile elementary spike intensity as a function of the arr ival time, and its observed duration, some qualitative considerations are a lso presented regarding the expected spectrum and on its departure from the thermal one. Tile results of this paper will be comparable, when data will become available, with a subfamily of particularly short GRBs not followed by ally afterglow. They can also be propedeutical to the study of longer b ursts in presence of baryonic matter currently observed in GRBs.