An upper limit on the luminosity of cosmological gamma‐ray bursts

The Pioneer Venus Orbiter (PVO) log N‐log P distribution follows a −3/2 power law for over a factor of 30 in intensity, which is inconsistent with Gamma‐Ray Bursts from large redshifts. We develop log N‐log P models suitable for cosmological gamma‐ray bursts. The PVO data is best fit with a standard candle peak luminosity of 2×1050 erg/sec with 3×104 events/yr within a Hubble distance. However, non‐cosmological models fit nearly as well (L0≪1050). A luminosity of 1052 erg/sec fits at a 3σ level and is, therefore, a maximum upper limit allowed by the PVO data. This upper limit is roughly equal to other reported lower limits. The BATSE event rate combined with the PVO limits imply that evolution with epoch must be occurring.