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Title: THE DISCOVERY OF A NEW INSTABILITY IN A HYPERACCRETION FLOW AND ITS IMPLICATION FOR GAMMA-RAY BURSTS

A hyperaccretion flow around a stellar mass black hole is thought to be the most plausible engine that powers gamma-ray bursts (GRBs). The flow efficiently cools via neutrino emission at ∼> 0.003-0.01 M {sub ☉} s{sup –1} (corresponding to a luminosity of ∼10{sup 50} erg s{sup –1}), while neither neutrino nor photon emission is efficient below this rate, so the flow should be advection-dominated. We carefully solve how a transition occurs from the advection-dominated to the neutrino-dominated branches, and find that the slope of the thermal equilibrium curve is negative in the surface density-accretion rate (Σ- M-dot ) plane, a condition for viscous instability, at radii smaller than ∼12 R {sub g} (with R {sub g} being the gravitational radius). We also confirm that the flow is thermally stable. The consequence of this instability is the formation of a clumpy structure in the flow. This is because the larger (respectively smaller) surface density is, the smaller (respectively larger) the mass accretion rate from the region in question becomes, leading to growth of the density contrast. The timescale for clump formation is estimated to be shorter than 0.1 s. The observational implication is discussed in the context of GRBs. We suggestmore » that this might explain the origin of the large variability observed in the prompt emission of GRBs.« less
Authors:
 [1] ;  [2] ;  [3]
  1. Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)
  2. Department of Astronomy, Kyoto University, Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto 606-8502 (Japan)
  3. Racah Institute of Physics, The Hebrew University, Jerusalem 91904 (Israel)
Publication Date:
OSTI Identifier:
22215386
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 777; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; ADVECTION; BLACK HOLES; COSMIC GAMMA BURSTS; DENSITY; INSTABILITY; LUMINOSITY; NEUTRINOS; PHOTON EMISSION; THERMAL EQUILIBRIUM