Search results for "MAGNETIC FIELD"
showing 10 items of 1488 documents
3D MHD modeling of the expanding remnant of SN 1987A : role of magnetic field and non-thermal radio emission
2018
Aims. We investigate the role played by a pre-supernova (SN) ambient magnetic field on the dynamics of the expanding remnant of SN 1987A and the origin and evolution of the radio emission from the remnant, in particular, during the interaction of the blast wave with the nebula surrounding the SN. Methods. We model the evolution of SN 1987A from the breakout of the shock wave at the stellar surface to the expansion of its remnant through the surrounding nebula by 3D MHD simulations. The model considers the radiative cooling, the deviations from equilibrium of ionization, the deviation from temperature-equilibration between electrons and ions, and a plausible configuration of the pre-SN ambie…
Axisymmetric simulations of magnetorotational core collapse: approximate inclusion of general relativistic effects
2006
We continue our investigations of the magnetorotational collapse of stellar cores discussing simulations performed with a modified Newtonian gravitational potential that mimics general relativistic effects. The approximate TOV potential used in our simulations catches several features of fully relativistic simulations quite well. It is able to correctly reproduce the behavior of models which show a qualitative change both of the dynamics and the gravitational wave signal when switching from Newtonian to fully relativistic simulations. If this is not the case, the Newtonian and the approximate TOV models differ quantitatively. The collapse proceeds to higher densities with the approximate TO…
On the Origin of Asymmetries in Bilateral Supernova Remnants
2007
AIMS: We investigate whether the morphology of bilateral supernova remnants (BSNRs) observed in the radio band is determined mainly either by a non-uniform interstellar medium (ISM) or by a non-uniform ambient magnetic field. METHODS: We perform 3-D MHD simulations of a spherical SNR shock propagating through a magnetized ISM. Two cases of shock propagation are considered: 1) through a gradient of ambient density with a uniform ambient magnetic field; 2) through a homogeneous medium with a gradient of ambient magnetic field strength. From the simulations, we synthesize the synchrotron radio emission, making different assumptions about the details of acceleration and injection of relativisti…
Laboratory evidence for proton energization by collisionless shock surfing
2021
Charged particles can be accelerated to high energies by collisionless shock waves in astrophysical environments, such as supernova remnants. By interacting with the magnetized ambient medium, these shocks can transfer energy to particles. Despite increasing efforts in the characterization of these shocks from satellite measurements at Earth’s bow shock as well as powerful numerical simulations, the underlying acceleration mechanism or a combination thereof is still widely debated. Here we show that astrophysically relevant super-critical quasi-perpendicular magnetized collisionless shocks can be produced and characterized in the laboratory. We observe the characteristics of super-criticali…
Radio polarization maps of shell-type SNRs II. Sedov models with evolution of turbulent magnetic field
2017
Polarized radio emission has been mapped with great detail in several Galactic supernova remnants (SNRs), but has not yet been exploited to the extent it deserves. We have developed a method to model maps of the Stokes parameters for shell-like SNRs during their Sedov evolution phase. At first, 3-dimensional structure of a SNR has been computed, by modeling the distribution of the magnetohydrodynamic parameters and of the accelerated particles. The generation and dissipation of the turbulent component of magnetic field everywhere in SNR are also considered taking into account its interaction with accelerated particles. Then, in order to model the emission, we have used a generalization of t…
Recollimation shocks in relativistic jets
2018
Recollimation shocks (RS) appear associated with relativistic flows propagating through pressure mismatched atmospheres. Astrophysical scenarios invoking the presence of such shocks include jets from AGNs and X-ray binaries and GRBs. We shall start reviewing the theoretical background behind the structure of RS in overpressured jets. Next, basing on numerical simulations, we will focus on the properties of RS in relativistic steady jets threaded by helical magnetic fields depending on the dominant type of energy. Synthetic radio maps from the simulation of the synchrotron emission for a selection of models in the context of parsec-scale extragalactic jets will also be discussed.© 2018 World…
Post-adiabatic supernova remnants in an interstellar magnetic field: oblique shocks and non-uniform environment
2018
Monthly notices of the Royal Astronomical Society 479(3), 4253 - 4270 (2018). doi:10.1093/mnras/sty1750
Probing the radio emission from air showers with polarization measurements
2014
The emission of radio waves from air showers has been attributed to the so-called geomagnetic emission process. At frequencies around 50 MHz this process leads to coherent radiation which can be observed with rather simple setups. The direction of the electric field induced by this emission process depends only on the local magnetic field vector and on the incoming direction of the air shower. We report on measurements of the electric field vector where, in addition to this geomagnetic component, another component has been observed which cannot be described by the geomagnetic emission process. The data provide strong evidence that the other electric field component is polarized radially wit…
Numerical investigation of the influence of EM-fields on fluid motion and resistivity distribution during floating-zone growth of large silicon singl…
2001
The floating-zone-process with needle-eye inductor is a complex process with many coupled parameters that have nonlinear influence on the process stability and resistivity distribution in the silicon single crystal. To fulfill the requirements of semiconductor industry for tighter specification of resistivity distribution, additional means like magnetic fields can be used to reach a more homogeneous resistivity distribution without disturbing process stability. The current paper analyses the influence of static and alternating fields on the fluid motion and macroscopic and microscopic resistivity profile by means of numerical calculations. It is found that with a lower frequency of the HF-i…
Applicability of LES turbulence modeling for CZ silicon crystal growth systems with traveling magnetic field
2010
Abstract To examine the applicability of LES turbulence modeling for CZ silicon crystal growth systems with traveling magnetic fields, LES calculations with Smagorinsky–Lilly turbulence model and van Driest damping at the solid walls are carried out. The program package for the calculations was developed on the basis of the open-source code library OpenFOAM ® . A previously published laboratory model with low temperature melt InGaSn, a 20” crucible, and process parameters corresponding to industrial Czochralski silicon systems is considered. Flow regimes with two crystal and crucible rotation rates and with different strengths of the traveling magnetic field “down” are analyzed. The calcula…