A Model for Most Luminous and Long Duration Cosmic Gamma Ray Bursts
  We exploit the fact that General Theory of Relativity (GTR) predicts the existence of compact objects having surface gravitational redshift z_s < =z_c=0.615 when the Equation of State (EOS) has the stringest general constraint that the speed of sound c_s < = 0.57 c. This z_c can be occur if a Neutron Star (NS) has a mass of ~2 M (solar) and radius ~8 Km, as is allowed by most of the existing EOSs. Thus massive spherical stars can indeed collapse to such (more compact) NSs. We have shown that the efficiency for production of electron-positron pairs out of the annihilation of resulting neutrino-antineutrino burst rises dramatically with the value of z_c and can saturate to ~40%. This may explain a gamma ray burst of energy as high as ~5. 10**53 erg. By using the already existing detailed (Newtonian) calculations, it follows that the neutrino heating driven mass loss should be negligible, and the bulk Lorentz factor of the initial fireball could be ~1000. Most of the existing supernova calculations also show that it is extremely difficult to simulate the direct neutrino driven mass loss, and, the shock is not launched if the gravitational field becomes stronger. Since the gravitation potential well of the more compact NS is indded very deep, we do not expect additional baryonic mass ejection. So, without invoking any exotic physics (like strange stars) or overstretching any theory, we may explain most of the luminous GRBs in this simple model. 
Abhas Mitra (BARC, Theory)