712 research outputs found
Relativistic Outflows in Gamma-Ray Bursts
The possibility that gamma-ray bursts (GRBs) were not isotropic emissions was
devised theoretically as a way to ameliorate the huge energetic budget implied
by the standard fireball model for these powerful phenomena. However, the
mechanism by which after the quasy-isotropic release of a few erg
yields a collimated ejection of plasma could not be satisfactory explained
analytically. The reason being that the collimation of an outflow by its
progenitor system depends on a very complex and non-linear dynamics. That has
made necessary the use of numerical simulations in order to shed some light on
the viability of some likely progenitors of GRBs. In this contribution I will
review the most relevant features shown by these numerical simulations and how
they have been used to validate the collapsar model (for long GRBs) and the
model involving the merger of compact binaries (for short GRBs).Comment: 8 pages, 1 figure. Proceedings of the conference: "Circumstellar
Media and Late Stages of Massive Stellar Evolution". Ensenada (Mexico). To be
published by Revista Mexicana de Astronomia y Astrofisic
Numerical study of broadband spectra caused by internal shocks in magnetized relativistic jets of blazars
The internal-shocks scenario in relativistic jets has been used to explain
the variability of blazars' outflow emission. Recent simulations have shown
that the magnetic field alters the dynamics of these shocks producing a whole
zoo of spectral energy density patterns. However, the role played by
magnetization in such high-energy emission is still not entirely understood.
With the aid of \emph{Fermi}'s second LAT AGN catalog, a comparison with
observations in the -ray band was performed, in order to identify the
effects of the magnetic field.Comment: Proceedings of the meeting The Innermost Regions of Relativistic Jets
and Their Magnetic Fields, June 10-14, 2013, Granada (Spain), 4 pages, 3
figure
Efficiency of internal shocks in magnetized relativistic jets
We study the dynamic and radiative efficiency of conversion of
kinetic-to-thermal/magnetic energy by internal shocks in relativistic
magnetized outflows. A parameter study of a large number of collisions of
cylindrical shells is performed. We explore how, while keeping the total flow
luminosity constant, the variable fluid magnetization influences the efficiency
and find that the interaction of shells in a mildly magnetized jet yields
higher dynamic, but lower radiative efficiency than in a non-magnetized flow. A
multi-wavelength radiative signature of different shell magnetization is
computed assuming that relativistic particles are accelerated at internal
shocks.Comment: 4 pages, 2 figures, proceedings of the meeting "HEPRO III: High
Energy Phenomena in Relativistic Outflows" (Barcelona, June 2011), fixed the
bibliography error
Simulations of the Magneto-rotational Instability in Core-Collapse Supernovae
We assess the importance of the magneto-rotational instability in
core-collapse supernovae by an analysis of the growth rates of unstable modes
in typical post-collapse systems and by numerical simulations of simplified
models. The interplay of differential rotation and thermal stratification
defines different instability regimes which we confirm in our simulations. We
investigate the termination of the growth of the MRI by parasitic
instabilities, establish scaling laws characterising the termination amplitude,
and study the long-term evolution of the saturated turbulent state.Comment: 6 pages, 1 figure. To appear in Proceedings of 4th International
Conference on Numerical Modeling of Space Plasma Flows (Chamonix 2009
Numerical simulations of the internal shock model in magnetized relativistic jets of blazars
The internal shocks scenario in relativistic jets is used to explain the
variability of the blazar emission. Recent studies have shown that the magnetic
field significantly alters the shell collision dynamics, producing a variety of
spectral energy distributions and light-curves patterns. However, the role
played by magnetization in such emission processes is still not entirely
understood. In this work we numerically solve the magnetohydodynamic evolution
of the magnetized shells collision, and determine the influence of the
magnetization on the observed radiation. Our procedure consists in
systematically varying the shell Lorentz factor, relative velocity, and viewing
angle. The calculations needed to produce the whole broadband spectral energy
distributions and light-curves are computationally expensive, and are achieved
using a high-performance parallel code.Comment: 7 pages, 5 figures, proceeding of the "Swift: 10 Years of Discovery"
conference (December 2014, Rome, Italy
A method for computing synchrotron and inverse-Compton emission from hydrodynamic simulations of supernova remnants
The observational signature of supernova remnants (SNRs) is very complex, in
terms of both their geometrical shape and their spectral properties, dominated
by non-thermal synchrotron and inverse-Compton scattering. We propose a
post-processing method to analyse the broad-band emission of SNRs based on
three-dimensional hydrodynamical simulations. From the hydrodynamical data, we
estimate the distribution of non-thermal electrons accelerated at the shock
wave and follow the subsequent evolution as they lose or gain energy by
adiabatic expansion or compression and emit energy by radiation. As a first
test case, we use a simulation of a bipolar supernova expanding into a cloudy
medium. We find that our method qualitatively reproduces the main observational
features of typical SNRs and produces fluxes that agree with observations to
within a factor of a few. allowing for further use in more extended sets of
models.Comment: 15 pages, 3 figures; accepted, HEDLA 2014 special issue of High
Energy Density Physic
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