2,114 research outputs found
A theory of the Io phase asymmetry of the Jovian decametric radiation
An explanation of an asymmetry in the occurrence probability of the Io-dependent Jovian decametric radiation is proposed. Io generates stronger Alfven waves toward the south when it is in the northern part of the torus. This wave then generates decametric radiation in the northern ionosphere after it reflects in the southern ionosphere. The asymmetry then results from computing the propagation time of the alfven wave along this trajectory. The ray paths of the decameter radiation are calculated using a three dimensional ray tracing program in the Jovian ionosphere. Variations in the expected probability plots are computer for two models of the Jovian ionosphere and global magnetic field, as well as for several choices of the ratio of the radiated frequency to the X-mode cutoff frequency
Plasma Jets and Eruptions in Solar Coronal Holes: a 3D flux emergence experiment
A three-dimensional numerical experiment of the launching of a hot and fast
coronal jet followed by several violent eruptions is analyzed in detail. These
events are initiated through the emergence of a magnetic flux rope from the
solar interior into a coronal hole. We explore the evolution of the emerging
magnetically-dominated plasma dome surmounted by a current sheet and the
ensuing pattern of reconnection. A hot and fast coronal jet with inverted-Y
shape is produced that shows properties comparable to those frequently observed
with EUV and X-Ray detectors. We analyze its 3D shape, its inhomogeneous
internal structure, and its rise and decay phases, lasting for some 15-20 min
each. Particular attention is devoted to the field-line connectivities and the
reconnection pattern. We also study the cool and high-density volume that
appears encircling the emerged dome. The decay of the jet is followed by a
violent phase with a total of five eruptions. The first of them seems to follow
the general pattern of tether-cutting reconnection in a sheared arcade,
although modified by the field topology created by the preceding reconnection
evolution. The two following eruptions take place near and above the strong
field-concentrations at the surface. They show a twisted, \Omega-loop like rope
expanding in height, with twist being turned into writhe, thus hinting at a
kink instability (perhaps combined with a torus-instability) as the cause of
the eruption. The succession of a main jet ejection and a number of violent
eruptions that resemble mini-CME's and their physical properties suggest that
this experiment may provide a model for the blowout jets recently proposed in
the literature.Comment: Accepted for publication in The Astrophysical Journal (vol 770, June
2013
A public code for general relativistic, polarised radiative transfer around spinning black holes
Ray tracing radiative transfer is a powerful method for comparing theoretical
models of black hole accretion flows and jets with observations. We present a
public code, grtrans, for carrying out such calculations in the Kerr metric,
including the full treatment of polarised radiative transfer and parallel
transport along geodesics. The code is written in Fortran 90 and efficiently
parallelises with OpenMP, and the full code and several components have Python
interfaces. We describe several tests which are used for verifiying the code,
and we compare the results for polarised thin accretion disc and semi-analytic
jet problems with those from the literature as examples of its use. Along the
way, we provide accurate fitting functions for polarised synchrotron emission
and transfer coefficients from thermal and power law distribution functions,
and compare results from numerical integration and quadrature solutions of the
polarised radiative transfer equations. We also show that all transfer
coefficients can play an important role in predicted images and polarisation
maps of the Galactic center black hole, Sgr A*, at submillimetre wavelengths.Comment: 22 pages, 12 figures, submitted to MNRAS. code available at:
github.com/jadexter/grtran
Self-consistent spectra from radiative GRMHD simulations of accretion onto Sgr A*
We present the first spectral energy distributions produced self-consistently
by 2.5D general relativistic magneto-hydrodynamical (GRMHD) numerical
simulations, where radiative cooling is included in the dynamical calculation.
As a case study, we focus on the accretion flow around the supermassive black
hole in the Galactic Centre, Sagittarius A* (Sgr A*), which has the best
constrained physical parameters. We compare the simulated spectra to the
observational data of Sgr A* and explore the parameter space of our model to
determine the effect of changing the initial magnetic field configuration, ion
to electron temperature ratio T_i/T_e and the target accretion rate. We find
the best description of the data for a mass accretion rate of ~ 1e-9 Msun/yr,
and rapid spin (0.7 < a_* < 0.9). The submillimeter peak flux seems largely
independent of initial conditions, while the higher energies can be very
sensitive to the initial magnetic field configuration. Finally, we also discuss
flaring features observed in some simulations, that may be due to artifacts of
the 2D configuration.Comment: Submitted to MNRAS. 13 pages, 15 figure
Gauge thresholds in the presence of oblique magnetic fluxes
We compute the one-loop partition function and analyze the conditions for
tadpole cancellation in type I theories compactified on tori in the presence of
internal oblique magnetic fields. We check open - closed string channel duality
and discuss the effect of T-duality. We address the issue of the quantum
consistency of the toroidal model with stabilized moduli recently proposed by
Antoniadis and Maillard (AM). We then pass to describe the computation of
one-loop threshold corrections to the gauge couplings in models of this kind.
Finally we briefly comment on coupling unification and dilaton stabilization in
phenomenologically more viable modelsComment: 34 pages, 2 figures; references added, major changes to the
discussion of the model proposed by Antoniadis and Maillar
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