On the nature of short and long gamma-ray bursts

For a long GRB (L-GRB) the induced gravitational collapse (IGC) paradigm proposes as progenitor a binary system made up of a carbon-oxygen core undergoing a supernova (SN) that triggers hypercritical accretion onto a neutron star (NS) companion. For a short GRB (S-GRB), a NS-NS merger is adopted. We divide L-GRBs and S-GRBs into subclasses, depending whether or not a black hole (BH) is formed. For long bursts, when no BH is formed we have the X-ray flashes (XRFs), with isotropic energy $E_{iso}\leq 10^{52}$ erg and rest-frame spectral peak energy $E_{p,i}\leq 200$ keV. When a BH is formed we have authentic L-GRBs, with $E_{iso}>10^{52}$ erg and $E_{p,i}>200$ keV. For short bursts, when no BH is formed we have short gamma-ray flashes (S-GRFs) with $E_{iso}\leq 10^{52}$ erg and $E_{p,i}\leq 2$ MeV, while an authentic S-GRBs occur if BH is formed, with $E_{iso}>10^{52}$ erg and $E_{p,i}>2$ MeV. We give examples and observational signatures of the four subclasses. In the case of S-GRBs and BdHNe evidence is given of the coincidence of the onset of the high-energy GeV emission with the birth of a Kerr-Newman BH. References: - R. Ruffini, 2015, Astron. Rep. 59, 591 - R. Ruffini, et al., 2015, ApJ 808, 190 - R. Ruffini, et al., 2015, ApJ 798, 10