GAMMA-RAY BURSTS FROM RELATIVISTIC JETS IN COCOONED ACTIVE GALACTIC NUCLEI AND GRAVITATIONAL LENSING TESTS OF THE COSMOLOGICAL ORIGIN

The beaming resulting from relativistic bulk motion can reduce by many orders of magnitude the energy requirements of burst sources and permit the escape of gamma-rays above 1 MeV even if the sources are located at cosmological distances. The X-ray emission is severely attenuated by the skewed energy distribution of the emitting particles and by the cocoon of material surrounding the massive black hole. The infrared afterglow from the burst source should be observable for hours and the quiescent source should be observable in the infrared. If the gamma-ray burst sources are at cosmological distances then the effects of gravitational lensing by foreground galaxies will be observed. These effects include (1) the observation of the same burst from the same source at separated times, (2) a discrepancy in the total flux for some bursts observed simultaneously by detectors separated by about 1 Astronomical Unit (AU) and (3) distortions of the bright ends of the V/V(max) and size-frequency distributions.