Testing the origin of the gamma-ray background

Fluctuations of the extragalactic gamma-ray background (EGB) are investigated. It is assumed that tile EGB is produced by the discrete sources. Two basic classes of objects as dominant contributors to the EGD are considered: a) blazars and b) starburst galaxies. Predicted log N - log S counts are calculated for these two models. In both cases strong cosmic evolution is needed to produce a substantial fraction of the observed EGB. Since on tile average blazars are several orders of magnitude more luminous than starburst galaxies, their number required to saturate the EGB is much smaller than the number of starburst galaxies. In effect, fluctuations of tile EGB in the blazar model are relatively high. It is shown that moderate improvement in the measurement accuracy of the EGB flux will allow us to discriminate between these models.