1,498 research outputs found
Asymmetric supernova remnants generated by Galactic, massive runaway stars
After the death of a runaway massive star, its supernova shock wave interacts
with the bow shocks produced by its defunct progenitor, and may lose energy,
momentum, and its spherical symmetry before expanding into the local
interstellar medium (ISM). We investigate whether the initial mass and space
velocity of these progenitors can be associated with asymmetric supernova
remnants. We run hydrodynamical models of supernovae exploding in the
pre-shaped medium of moving Galactic core-collapse progenitors. We find that
bow shocks that accumulate more than about 1.5 Mo generate asymmetric remnants.
The shock wave first collides with these bow shocks 160-750 yr after the
supernova, and the collision lasts until 830-4900 yr. The shock wave is then
located 1.35-5 pc from the center of the explosion, and it expands freely into
the ISM, whereas in the opposite direction it is channelled into the region of
undisturbed wind material. This applies to an initially 20 Mo progenitor moving
with velocity 20 km/s and to our initially 40 Mo progenitor. These remnants
generate mixing of ISM gas, stellar wind and supernova ejecta that is
particularly important upstream from the center of the explosion. Their
lightcurves are dominated by emission from optically-thin cooling and by X-ray
emission of the shocked ISM gas. We find that these remnants are likely to be
observed in the [OIII] lambda 5007 spectral line emission or in the soft
energy-band of X-rays. Finally, we discuss our results in the context of
observed Galactic supernova remnants such as 3C391 and the Cygnus Loop.Comment: 21 pages, 16 figure
Photo-ionization of planetary winds: case study HD209458b
Close-in hot Jupiters are exposed to a tremendous photon flux that ionizes
the neutral escaping material from the planet leaving an observable imprint
that makes them an interesting laboratory for testing theoretical models. In
this work we present 3D hydrodynamic simulations with radiation transfer
calculations of a close-in exoplanet in a blow-off state. We calculate the
Ly- absorption and compare it with observations of HD 209458b an
previous simplified model results.Our results show that the hydrodynamic
interaction together with a proper calculation of the photoionization proccess
are able to reproduce the main features of the observed Ly- absorption,
in particular at the blue-shifted wings of the line. We found that the ionizing
stellar flux produce an almost linear effect on the amount of absorption in the
wake. Varying the planetary mass loss rate and the radiation flux, we were able
to reproduce the absorption observed at .Comment: 9 pages, 6 figure
Origin of the bilateral structure of the supernova remnant G296.5+10
In this work, we have modelled the supernova remnant (SNR) G296.5+10, by means of 3D magnetohydrodynamics (MHD) simulations. This remnant belongs to the bilateral SNR group and has an additional striking feature: the rotation measure (RM) in its eastern and western parts are very different. In order to explain both the morphology observed in radio-continuum and the RM, we consider that the remnant expands into a medium shaped by the superposition of the magnetic field of the progenitor star with a constant Galactic magnetic field. We have also carried out a polarization study from our MHD results, obtaining synthetic maps of the linearly polarized intensity and the Stokes parameters. This study reveals that both the radio morphology and the reported RM for G296.5+10 can be explained if the quasi-parallel acceleration mechanism is taking place in the shock front of this remnant.Fil: Moranchel-Basurto, A.. Universidad Nacional Autónoma de México; MéxicoFil: Velazquez, P.. Universidad Nacional Autónoma de México; MéxicoFil: Giacani, Elsa Beatriz. Universidad de Buenos Aires. Facultad de Arquitectura y Urbanismo; Argentina. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Toledo Roy, J. C.. Universidad Nacional Autónoma de México; MéxicoFil: Schneiter, E.. Universidad Nacional Autónoma de México; MéxicoFil: De Colle, F.. Universidad Nacional Autónoma de México; MéxicoFil: Esquivel, A.. Universidad Nacional Autónoma de México; Méxic
Instabilities and Clumping in Type Ia Supernova Remnants
We present two-dimensional high-resolution hydrodynamical simulations in
spherical polar coordinates of a Type Ia supernova interacting with a constant
density interstellar medium. The ejecta are assumed to be freely expanding with
an exponential density profile. The interaction gives rise to a double-shocked
structure susceptible to hydrodynamic instabilities. The Rayleigh-Taylor
instability initially grows, but the Kelvin-Helmholtz instability takes over,
producing vortex rings. The nonlinear instability initially evolves toward
longer wavelengths and eventually fades away when the reverse shock front is in
the flatter part of the supernova density distribution. Based on observations
of X-ray knots and the protrusion in the southeast outlin of Tycho's supernova
remnant, we include clumping in the ejecta. The clump interaction with the
reverse shock induces Rayleigh-Taylor and Kelvin-Helmholtz instabilities on the
clump surface that facilitate fragmentation. In order to survive crushing and
to have a bulging effect on the forward shock, the clump's initial density
ratio to the surrounding ejecta must be at least 100 for the conditions in
Tycho's remnant. The 56Ni bubble effect may be important for the development of
clumpiness in the ejecta. The observed presence of an Fe clump would then
require a non-radioactive origin for this Fe, possibly 54Fe. The large radial
distance of the X-ray emitting Si and S ejecta from the remnant center
indicates that they were initially in clumps.Comment: 27 pages, 4 postscript figures, 5 GIF figures submitted to
Astrophysical Journa
A Supernova Remnant Collision with a Stellar Wind
Numerical simulations of the interaction between supernova ejecta and a
stellar wind are presented. We follow the temporal evolution of the shock
fronts that are formed through such an interaction and determine the
velocities, temperatures and densities. We model the X-ray emission from the
SNR-stellar wind collision region and we compare it with recent results from
X-ray observations carried out with the Chandra satellite of the SMC supernova
remnant SNR 0057-7226 which could be interacting with the wind of the
Wolf-Rayet system HD 5980. The simulations predict the presence of shell-like
regions of enhanced X-ray emission which are consistent with the presence of
X-ray emitting arcs in the Chandra image. Also the observed X-ray luminosity is
comparable to the X-ray luminosities we obtain from the simulations for a
supernova with an initial energy in the (1-5)E50 erg range.Comment: 9 files into a tar.gz file (the Latex file of manuscript, 7 jpg
figures, 1 style file: aastex.cls). Accepted by ApJ, Vol. 584, 2003 February
1
A blowout numerical model for the supernova remnant G352.7-0.1
We present 3D hydrodynamical simulations of the Galactic supernova remnant G352.7−0.1. This remnant is peculiar for having a shell-like inner ring structure and an outer arc in radio observations. In our model, the supernova explosion producing the remnant occurs inside and near the border of a spherical cloud with a density higher than that of the surrounding interstellar medium. A blowout is produced when the remnant reaches the border of the cloud. We have then used the results of our hydrodynamical simulations to calculate synthetic synchrotron radio emission maps, as well as synthetic X-ray maps. For some combinations
of the particle acceleration mechanism and the direction of the line of sight, our radio maps display the peculiar morphology of G352.7−0.1 and reproduce the correct relative sizes of the main observed features. At the same time, the calculated X-ray maps reproduce the centrally peaked morphology of the observations.Fil: Toledo Roy, J. C.. Universidad Nacional Autónoma de México; MéxicoFil: Velazquez, P. F.. Universidad Nacional Autónoma de México; MéxicoFil: Esquivel, A.. Universidad Nacional Autónoma de México; MéxicoFil: Giacani, Elsa Beatriz. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentin
A 3D numerical model for Kepler's supernova remnant
We present new 3D numerical simulations for Kepler´s supernova remnant. In this work we revisit the possibility that the asymmetric shape of the remnant in X-rays is the product of a type Ia supernova explosion which occurs inside the wind bubble previously created by an AGB companion star. Due to the large peculiar velocity of the system, the interaction of the strong AGB wind with the interstellar medium results in a bow shock structure. In this new model we propose that the AGB wind is anisotropic, with properties such as mass-loss rate and density having a latitude dependence, and that the orientation of the polar axis of the AGB star is not aligned with the direction of motion. The ejecta from the type Ia supernova explosion is modeled using a power-law density prole, and we let the remnant evolve for 400 yr. We computed synthetic X-ray maps from the numerical results. We find that the estimated size and peculiar X-ray morphology of Kepler´s SNR are well reproduced by considering an AGB mass-loss rate of 10-5 M_sol yr-1, a wind terminal velocity of 10 km s-1, an ambient medium density of 10-3 cm^3 and an explosion energy of 7x10^50 erg. The obtained total X-ray luminosity of the remnant in this model reaches 6x10^50 erg, which is within a factor of two of the observed value, and the time evolution of the luminosity shows a rate of decrease in recent decades of ~2.4% yr-1 that is consistent with the observations.Fil: Toledo Roy, J. C.. Universidad Nacional Autónoma de México. Instituto de Ciencias Nucleares; MéxicoFil: Esquivel, A.. Universidad Nacional Autónoma de México. Instituto de Ciencias Nucleares; MéxicoFil: Velazquez, P. F.. Universidad Nacional Autónoma de México. Instituto de Ciencias Nucleares; MéxicoFil: Reynoso, Estela Marta. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentin
Cosmic Ray Acceleration at the Forward Shock in Tycho's Supernova Remnant: Evidence from Chandra X-ray Observations
We present evidence for cosmic ray acceleration at the forward shock in
Tycho's supernova remnant (SNR) from three X-ray observables: (1) the proximity
of the contact discontinuity to the forward shock, or blast wave, (2) the
morphology of the emission from the rim of Tycho, and (3) the spectral nature
of the rim emission. We determine the locations of the blast wave (BW), contact
discontinuity (CD), and reverse shock (RS) around the rim of Tycho's supernova
remnant using a principal component analysis and other methods applied to new
Chandra data. The azimuthal-angle-averaged radius of the BW is 251". For the CD
and RS we find average radii of 241" and 183", respectively. Taking account of
projection effects, we find ratios of 1:0.93:0.70 (BW:CD:RS). We show these
values to be inconsistent with adiabatic hydrodynamical models of SNR
evolution. The CD:BW ratio can be explained if cosmic ray acceleration of ions
is occurring at the forward shock. The RS:BW ratio, as well as the strong Fe Ka
emission from the Tycho ejecta, imply that the RS is not accelerating cosmic
rays. We also extract radial profiles from ~34% of the rim of Tycho and compare
them to models of surface brightness profiles behind the BW for a purely
thermal plasma with an adiabatic shock. The observed morphology of the rim is
much more strongly peaked than predicted by the model, indicating that such
thermal emission is implausible here. Spectral analysis also implies that the
rim emission is non-thermal in nature, lending further support to the idea that
Tycho's forward shock is accelerating cosmic rays.Comment: 39 pages, 10 figures, accepted by Ap
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