arXiv subjects

Andrei Gruzinov

Publications and source records attributed to Andrei Gruzinov.

98 records · Page 6Linked to original sources

arXiv1999

Strongly Polarized Optical Afterglows of Gamma-Ray Bursts

The optical afterglows of the gamma ray bursts can be strongly polarized, in principle up to tens of percents, if: (i) the afterglow is synchrotron radiation from an ultra-relativistic blast, (ii) the blast is beamed during the afterglow phase, i.e. the shock propagates within a narrow jet, (iii) we observe at the right time from the right viewing angle, (iv) magnetic fields parallel and perpendicular to the jet have different proper strengths.

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arXiv1999

Stability in Force-Free Electrodynamics

We show that flows of pure electromagnetic energy are subject to instabilities familiar from hydrodynamics and plasma physics---Kelvin-Helmholtz and screw instabilities. In the framework of force-free electrodynamics, it is found that electric-like tangential discontinuities are Kelvin-Helmholtz-unstable. All non-trivial cylindrically symmetrical magnetic configurations are screw-unstable. The Poynting jet of the Goldreich-Julian pulsar is screw-unstable if the current density in the polar cap region exceeds the charge density times the speed of light. This may be the process that determines the pulsar luminosity.

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arXiv1998

The Rate of Turbulent Spherical Accretion

The rate of turbulent spherical accretion onto a compact object might be much smaller than the Bondi rate. It is suggested that the rate of accretion onto Sgr A-star is much smaller than the Bondi rate.

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arXiv1998

The Proton Distribution Function in Weakly Magnetized Turbulent Plasmas

We calculate the proton distribution function due to heating by subsonic (Alfvenic) turbulence in a weakly magnetized collisionless plasma. The distribution function is nonthermal. For non-relativistic energies, it is an exponential of the magnitude of the proton velocity. For ultra-relativistic energies, it can be characterized as a power law with a momentum-dependent slope.

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arXiv1998

Frequency Shifts of the Solar Fundamental Mode

The observed frequency shifts of the high-degree solar fundamental mode are explained using a simple geometrical optics approximation. The predicted fractional frequency shift is proportional to the mean squared velocity of the convection flow at the surface of the Sun and inversely proportional to the group velocity of the mode squared. The data converge to the predicted behavior at very high degrees. The inferred root mean squared convection velocity is 1.3 km/s.

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arXiv1998

Gamma-Ray Burst Afterglow: Polarization and Analytic Light Curves

GRB afterglow polarization is discussed. We find an observable, up to 10%, polarization, if the magnetic field coherence length grows at about the speed of light after the field is generated at the shock front. Detection of a polarized afterglow would show that collisionless ultrarelativistic shocks can generate strong large scale magnetic fields and confirm the synchrotron afterglow model. Non-detection, at a 1% level, would imply that either the synchrotron emission model is incorrect, or that strong magnetic fields, after they are generated in the shock, somehow manage to stay un-dissipated at ``microscopic'', skin depth, scales. Analytic lightcurves of synchrotron emission from an ultrarelativistic self-similar blast wave are obtained for an arbitrary electron distribution function, taking into account the effects of synchrotron cooling. The peak synchrotron flux and the flux at frequencies much smaller than the peak frequency are insensitive to the details of the electron distribution function; hence their observational determination would provide strong constraints on blast wave parameters.

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arXiv1998

Secondary CMB anisotropies in a universe reionized in patches

In a universe reionized in patches, the Doppler effect from Thomson scattering off free electrons generates secondary cosmic microwave background (CMB) anisotropies. For a simple model with small patches and late reionization, we analytically calculate the anisotropy power spectrum. Patchy reionization can, in principle, be the main source of anisotropies on arcminute scales. On larger angular scales, its contribution to the CMB power spectrum is a small fraction of the primary signal and is only barely detectable in the power spectrum with even an ideal, i.e. cosmic variance limited, experiment and an extreme model of reionization. Consequently patchy reionization is unlikely to affect cosmological parameter estimation from the acoustic peaks in the CMB. Its detection on small angles would help determine the ionization history of the universe, in particular the typical size of the ionized region and the duration of the reionization process.

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arXiv1998

Turbulence and Particle Heating in Advection-Dominated Accretion Flows

We extend and reconcile recent work on turbulence and particle heating in advection-dominated accretion flows. For approximately equipartition magnetic fields, the turbulence primarily heats the electrons. For weaker magnetic fields, the protons are primarily heated. The division between electron and proton heating occurs between $β\sim 5$ and $β\sim 100$ (where $β$ is the ratio of the gas to the magnetic pressure), depending on unknown details of how Alfvén waves are converted into whistlers on scales of the proton Larmor radius. We also discuss the possibility that magnetic reconnection could be a significant source of electron heating.

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