$\\gamma$ Ray Bursts $vs.$ Afterglows

Abstract. When does a GRB stop and its afterglow be-gin? A GRB may be dened as emission by internal shocks and its afterglow as emission by an external shock, but it is necessary to distinguish them observationally. With these denitions irregularly varying emission (at any fre-quency) must be the GRB, but smoothly varying intensity is usually afterglow. The GRB itself and its afterglow may overlap in time and in frequency, and distinguishing them will, in general, require detailed modeling. Key words: gamma-ray bursts | shock waves At rst glance there appears to be little diculty in distinguishing between GRB and their afterglows. GRB were discovered in 1972, and are observed in gamma-rays with detectors most sensitive to photons in the range 100 − 1000 keV. The observed durations of GRB range