8 research outputs found
General Relativistic Ray-Tracing Method for Estimating the Energy and Momentum Deposition by Neutrino Pair Annihilation in Collapsars
Bearing in mind the application to the collapsar models of gamma-ray bursts
(GRBs), we develop a numerical scheme and code for estimating the deposition of
energy and momentum due to the neutrino pair annihilation () in the vicinity of accretion tori around a Kerr
black hole. Our code is designed to solve the general relativistic neutrino
transfer by a ray-tracing method. To solve the collisional Boltzmann equation
in curved spacetime, we numerically integrate the so-called rendering equation
along the null geodesics. For the neutrino opacity, the charged-current
-processes are taken into account, which are dominant in the vicinity of
the accretion tori. The numerical accuracy of the developed code is
certificated by several tests, in which we show comparisons with the
corresponding analytic solutions. Based on the hydrodynamical data in our
collapsar simulation, we estimate the annihilation rates in a post-processing
manner. Increasing the Kerr parameter from 0 to 1, it is found that the general
relativistic effect can increase the local energy deposition rate by about one
order of magnitude, and the net energy deposition rate by several tens of
percents. After the accretion disk settles into a stationary state (typically
later than s from the onset of gravitational collapse), we point out
that the neutrino-heating timescale in the vicinity of the polar funnel region
can be shorter than the dynamical timescale. Our results suggest the neutrino
pair annihilation has a potential importance equal to the conventional
magnetohydrodynamic mechanism for igniting the GRB fireballs.Comment: 33 pages, 15 figures, accepted to the Ap
Gravitational Wave Signatures of Hyperaccreting Collapsar Disks
By performing two-dimensional special relativistic (SR) magnetohydrodynamic
simulations, we study possible signatures of gravitational waves (GWs) in the
context of the collapsar model for long-duration gamma-ray bursts. In our SR
simulations, the central black hole is treated as an absorbing boundary. By
doing so, we focus on the GWs generated by asphericities in neutrino emission
and matter motions in the vicinity of the hyperaccreting disks. We compute nine
models by adding initial angular momenta and magnetic fields parametrically to
a precollapse core of a progenitor star. As for the
microphysics, a realistic equation of state is employed and the neutrino
cooling is taken into account via a multiflavor neutrino leakage scheme. To
accurately estimate GWs produced by anisotropic neutrino emission, we perform a
ray-tracing analysis in general relativity by a post-processing procedure. By
employing a stress formula that includes contributions both from magnetic
fields and special relativistic corrections, we study also the effects of
magnetic fields on the gravitational waveforms. We find that the GW amplitudes
from anisotropic neutrino emission show a monotonic increase with time, whose
amplitudes are much larger than those from matter motions of the accreting
material. We show that the increasing trend of the neutrino GWs stems from the
excess of neutrino emission in the direction near parallel to the spin axis
illuminated from the hyperaccreting disks. We point out that a recently
proposed future space-based interferometer like Fabry-Perot type DECIGO would
permit the detection of these GW signals within 100 Mpc.Comment: 38 pages, 14 figures, ApJ in pres