On the classification of GRBs and their occurrence rates
- Dipartimento di Fisica and ICRA, Sapienza Università di Roma, Piazzale Aldo Moro 5, I-00185 Rome (Italy)
There is mounting evidence for the binary nature of the progenitors of gamma-ray bursts (GRBs). For a long GRB, the induced gravitational collapse paradigm proposes as progenitor, or “in-state,” a tight binary system composed of a carbon–oxygen core (CO{sub core}) undergoing a supernova explosion that triggers hypercritical accretion onto a neutron star (NS) companion. For a short GRB (S-GRB), an NS–NS merger is traditionally adopted as the progenitor. We divide long and S-GRBs into two subclasses, depending on whether or not a black hole (BH) is formed in the merger or in the hypercritical accretion process exceeding the NS critical mass. For long bursts, when no BH is formed, we have the subclass of X-ray flashes (XRFs), with isotropic energy E{sub iso}≲10{sup 52} erg and rest-frame spectral peak energy E{sub p,i}≲200 keV. When a BH is formed, we have the subclass of binary-driven hypernovae (BdHNe), with E{sub iso}≳10{sup 52} erg and E{sub p,i}≳200 keV. In analogy, short bursts are similarly divided into two subclasses. When no BH is formed, short gamma-ray flashes (S-GRFs) occur, with E{sub iso}≲10{sup 52} erg and E{sub p,i}≲2 MeV. When a BH is formed, the authentic S-GRBs occur, with E{sub iso}≳10{sup 52} erg and E{sub p,i}≳2 MeV. We give examples and observational signatures of these four subclasses and their rate of occurrence. From their respective rates it is possible that “in-states” of S-GRFs and S-GRBs originate from the “out-states” of XRFs. We indicate two additional progenitor systems: white dwarf–NS and BH–NS. These systems have hybrid features between long and short bursts. 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 BH.
- OSTI ID:
- 22868422
- Journal Information:
- Astrophysical Journal, Vol. 832, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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