TY - JOUR
T1 - Accretion models of gamma-ray bursts
AU - Narayan, Ramesh
AU - Piran, Tsvi
AU - Kumar, Pawan
PY - 2001/8/20
Y1 - 2001/8/20
N2 - Many models of gamma-ray bursts (GRBs) involve accretion onto a compact object, usually a black hole, at a mass accretion rate on the order of a fraction of a solar mass per second. If the accretion disk is larger than a few tens or hundreds of Schwarzschild radii, the accretion will proceed via a convection-dominated accretion flow (CDAF) in which most of the matter escapes to infinity rather than falling onto the black hole. Models involving the mergers of black hole-white dwarf binaries and black hole-helium star binaries fall in this category. These models are unlikely to produce GRBs since very little mass reaches the black hole. If the accretion disk is smaller, then accretion will proceed via neutrino cooling in a neutrino-dominated accretion disk (NDAF) and most of the mass will reach the center. Models involving the mergers of double neutron star binaries and black hole-neutron star binaries fall in this category and are capable of producing bright GRBs. If the viscosity parameter α in the NDAF has a standard value of ∼0.1, these mergers can explain short GRBs with durations under a second, but they are unlikely to produce long GRBs with durations of tens or hundred of seconds. If the accretion disk is fed by fallback of material after a supernova explosion, as in the collapsar model, then the time-scale of the burst is determined by fallback, not accretion. Such a model can produce long GRBs. Fallback models again require that the accretion should proceed via an NDAF rather than a CDAF in order for a significant amount of mass to reach the black hole. This condition imposes an upper limit on the radius of injection of the gas.
AB - Many models of gamma-ray bursts (GRBs) involve accretion onto a compact object, usually a black hole, at a mass accretion rate on the order of a fraction of a solar mass per second. If the accretion disk is larger than a few tens or hundreds of Schwarzschild radii, the accretion will proceed via a convection-dominated accretion flow (CDAF) in which most of the matter escapes to infinity rather than falling onto the black hole. Models involving the mergers of black hole-white dwarf binaries and black hole-helium star binaries fall in this category. These models are unlikely to produce GRBs since very little mass reaches the black hole. If the accretion disk is smaller, then accretion will proceed via neutrino cooling in a neutrino-dominated accretion disk (NDAF) and most of the mass will reach the center. Models involving the mergers of double neutron star binaries and black hole-neutron star binaries fall in this category and are capable of producing bright GRBs. If the viscosity parameter α in the NDAF has a standard value of ∼0.1, these mergers can explain short GRBs with durations under a second, but they are unlikely to produce long GRBs with durations of tens or hundred of seconds. If the accretion disk is fed by fallback of material after a supernova explosion, as in the collapsar model, then the time-scale of the burst is determined by fallback, not accretion. Such a model can produce long GRBs. Fallback models again require that the accretion should proceed via an NDAF rather than a CDAF in order for a significant amount of mass to reach the black hole. This condition imposes an upper limit on the radius of injection of the gas.
KW - Accretion, accretion disks
KW - Gamma rays: Bursts
KW - Gamma rays: Theory
UR - http://www.scopus.com/inward/record.url?scp=0035921215&partnerID=8YFLogxK
U2 - 10.1086/322267
DO - 10.1086/322267
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AN - SCOPUS:0035921215
SN - 0004-637X
VL - 557
SP - 949
EP - 957
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2 PART 1
ER -