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5. GAMMA RAY BURSTS

The contribution of untriggered GRBs to the gamma-ray background can be estimated in a number of ways, but all depend on modeling, or inferring from observations, the typical high-energy GRB spectra. For the optimistic case that the TeV flux made by a GRB is approx 10 &215; greater than the MeV flux, then the superpositions of GRB emissions are found to make approx 10% of the gamma-ray background after cascading from high energies into the GeV band [9]. If one instead relies on observations of EGRET spark-chamber GRBs that show that the fluence in the EGRET band is only approx 10% of the fluence in the BATSE band, then GRBs are found to give very little (ltapprox 1%) contribution to the gamma-ray background [25]. This neglects the contributions of short, hard GRBs and low luminosity GRBs, but since these have small fluences and all-sky rates, they are unlikely to make a significant contribution to the gamma-ray background.

It hardly needs to be mentioned that GLAST observations of the high-energy emission from GRBs will provide crucial information to determine the share of the background gamma-ray intensity provided by GRBs.