How does a Secular Instability Grow in a Hyperaccretion Flow?

Abstract

Hyperaccretion flows with mass accretion rates far above the Eddington rate have an N-shaped equilibrium curve on the $\Sigma$-$\dot{M}$ plane (with $\Sigma$ and $\dot{M}$ being surface density and mass accretion rate, respectively). The accretion flow on the lower $\Sigma$ branch of the N-shape is optically thick, advection-dominated accretion flow (ADAF) while that on the upper one is neutrino-dominated accretion flow (NDAF). The middle branch has a negative slope on the $\Sigma$-$\dot{M}$ plane, meaning that the flow on this branch is secularly unstable. To investigate how the instability affects the flow structure and what observable signatures are produced, we study the time evolution of the unstable hyperaccretion flow in response to variable mass injection rates by solving the height-averaged equations for viscous accretion flows. When a transition occurs from the lower branch to the upper branch (or from the upper branch to the lower branch), the surface density rapidly increases (decreases) around that transition region, which induces locally enhanced mass flow (referred to as non-steady mass flow) into (out of) that region. We confirm that the non-steady flow can create a kind of disturbance and that it propagates over the whole disk. However, the non-steady mass flow is not strong enough to induce coherent transition over the whole disk, unless the mass injection rate varies with time. When the injection rate continuously changes, the neutrino luminosity varies intermittently, thus producing step-function-like light curves, as the radiation efficiency discontinuously changes every time the local transition occurs. The effects of changing the N-shape and possible observational consequences on the gamma-ray burst emission are briefly discussed in relation to gamma-ray bursts.

14 pages, 27 figures, accepted for publication in PASJ

References in corpus (7)

• Neutrino-Cooled Accretion Disks around Spinning Black Hole
• Neutrino-Dominated Accretion Models for Gamma-Ray Bursts: Effects of General Relativity and Neutrino Opacity
• Jet Luminosity From Neutrino-Dominated Accretion Flows in Gamma-Ray Bursts
• Relativistic global solutions of neutrino-dominated accretion flows
• Swift and Fermi observations of X-ray flares: the case of Late Internal Shock
• The Discovery of a New Instability in a Hyperaccretion Flow and its Implication for Gamma-ray Bursts
• Neutrino Acceleration by Bulk Matter Motion and Explosion Mechanism of Gamma-Ray Bursts

Cited by in corpus (4)

• Neutrino-dominated accretion flows as the central engine of gamma-ray bursts
• Variabilities of Gamma-ray Bursts from Black Hole Hyper-accretion Disks
• Neutrino-Dominated Accretion Flows with Magnetic Prandtl Number-Dependent MRI-driven Turbulence
• Relativistic global solutions of neutrino-dominated accretion flows with magnetic coupling