THREE-DIMENSIONAL SIMULATIONS OF MAGNETOHYDRODYNAMIC TURBULENCE BEHIND RELATIVISTIC SHOCK WAVES AND THEIR IMPLICATIONS FOR GAMMA-RAY BURSTS

Journal Article · Mon Jun 20 00:00:00 EDT 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/734/2/77· OSTI ID:21576623

Inoue, Tsuyoshi ^[1]; Asano, Katsuaki ^[2]; Ioka, Kunihito ^[3]

---

1. Department of Physics and Mathematics, Aoyama Gakuin University, Fuchinobe, Chuou-ku, Sagamihara 252-5258 (Japan)
2. Interactive Research Center of Science, Graduate School of Science, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152-8550 (Japan)
3. KEK Theory Center and the Graduate University for Advanced Studies, Oho, Tsukuba 305-0801 (Japan)

Relativistic astrophysical phenomena such as gamma-ray bursts (GRBs) and active galactic nuclei often require long-lived strong magnetic fields that cannot be achieved by shock compression alone. Here, we report on three-dimensional special-relativistic magnetohydrodynamic (MHD) simulations that we performed using a second-order Godunov-type conservative code to explore the amplification and decay of macroscopic turbulence dynamo excited by the so-called Richtmyer-Meshkov instability (RMI; a Rayleigh-Taylor-type instability). This instability is an inevitable outcome of interactions between shock and ambient density fluctuations. We find that the magnetic energy grows exponentially in a few eddy-turnover times because of field-line stretching and then, following the decay of kinetic turbulence, decays with a temporal power-law exponent of -0.7. The magnetic energy fraction can reach {epsilon}{sub B} {approx} 0.1 but depends on the initial magnetic field strength, which can diversify the observed phenomena. We find that the magnetic energy grows by at least two orders of magnitude compared to the magnetic energy immediately behind the shock, provided the kinetic energy of turbulence injected by the RMI is greater than the magnetic energy. This minimum degree of amplification does not depend on the amplitude of the initial density fluctuations, while the growth timescale and the maximum magnetic energy depend on the degree of inhomogeneity in the density. The transition from Kolmogorov cascade to MHD critical balance cascade occurs at {approx}1/10th the initial inhomogeneity scale, which limits the maximum synchrotron polarization to less than {approx}2%. We derive analytical formulas for these numerical results and apply them to GRBs. New results include the avoidance of electron cooling with RMI turbulence, the turbulent photosphere model via RMI, and the shallow decay of the early afterglow from RMI. We also perform a simulation of freely decaying turbulence with relativistic velocity dispersion. We find that relativistic turbulence begins to decay much more quickly than one eddy-turnover time because of rapid shock dissipation, which does not support the relativistic turbulence model by Narayan and Kumar.

• OSTI ID: 21576623
• Journal Information: Astrophysical Journal, Vol. 734, Issue 2; Other Information: DOI: 10.1088/0004-637X/734/2/77; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
COSMIC GAMMA BURSTS
DENSITY
FLUCTUATIONS
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS
RAYLEIGH-TAYLOR INSTABILITY
SHOCK WAVES
SIMULATION
THREE-DIMENSIONAL CALCULATIONS
TURBULENCE
COSMIC RADIATION
FLUID MECHANICS
HYDRODYNAMICS
INSTABILITY
IONIZING RADIATIONS
MECHANICS
PHYSICAL PROPERTIES
PRIMARY COSMIC RADIATION
RADIATIONS
VARIATIONS