Interaction of Supernova Remnants with a Circumstellar Shell - V. V. Dwarkadas,1995, AAS 187th Meeting

ABSTRACT: We are studying the interaction of supernova remnants (SNRs) with circumstellar shells, with an emphasis on Type II supernovae (SNe). These supernovae arise from massive progenitor stars (> 8 Msun), which lose mass during their lifetime, primarily in the form of a stellar wind. Often the stellar wind creates a circumstellar bubble surrounded by a dense shell. When the star explodes as a supernova, the resulting shock wave eventually collides with this dense shell. In a recent paper on SN 1987A (Chevalier & Dwarkadas, ApJL, 452, L45) we have shown that from the radio and X-ray emission, one can infer the presence of a high density region interior to the dense circumstellar shell. This can be explained as an HII region photoionized by the flux from the pre-supernova star. Using the Zeus code and assuming spherical symmetry, we have studied the dynamics of the shock wave interacting first with the HII region and then the circumstellar shell in SN 1987A. Collision with the HII region results in a significant deceleration of the shock wave, forming a high-density shocked region that grows with time, and is primarily responsible for the X-ray emission. X-ray emission from the reflected shock may begin to dominate when the forward shock hits the dense circumstellar shell and is considerably slowed down. Simulations are in progress with parameters suited to other remnants such as Cas A and W44. Radio and X-ray images of Cas A show a shell structure, which may result from interaction with a stellar bubble. W44 also shows a double-shell structure that may have been produced by a SN explosion inside a pre-existing wind bubble. The interaction is subject to instabilities that may give rise to filamentary structure.


PASA, Vol 17, #1

                 Vikram Dwarkadas , Lewis Ball , James Caswell , Anne Green , Simon Johnston , Brian Schmidt , Mark Wardle

ABSTRACT: We summarise the proceedings of the SRCfTA workshop on ``Supernova Remnants, Pulsars and the Interstellar Medium'' that was held at the University of Sydney on Mar 18 and 19, 1999.

Interaction of Supernova Remnants with the Ambient Medium

Vikram V. Dwarkadas, 2001, JKAS, 34, 243

ABSTRACT: We summarize various aspects of the interaction of supernova remnants (SNRs) with the ambient medium. We discuss the evolution of SNRs in environments sculpted by the progenitor star, and summarize the factors on which this evolution depends. As a specific example, we consider the evolution of the medium around a 35Msun star, and the interaction of the shock wave with this medium when the star explodes as a SN. We also discuss the interaction of Type Ia SNe with the ambient medium, especially the formation and growth of hydrodynamic instabilities.

The Interaction of Supernova Shock Waves with Circumstellar Wind-Blown Bubbles

Vikram V. Dwarkadas, 2002, in Interacting Winds from Massive Stars. ASP Conference Proceedings, Vol. 260. Edited by Anthony F. J. Moffat and Nicole St-Louis, p.141

Abstract: During their lifetime, massive stars lose considerable mass in the form of stellar winds. These winds may evacuate a cavity in the surrounding medium, bordered by a dense shell. If the star ends its life in a supernova explosion, the resulting shock wave will interact with this shell. The subsequent evolution of the supernova remnant depends in particular on the ratio of the mass of the shell to the ejecta mass. Using numerical techniques this evolution is studied for a range of parameter values.

The Evolution of Supernovae in the Winds of Massive Stars

Vikram V. Dwarkadas, 2003, in procedings of 3-D Signatures in Stellar Explosions, A Workshop Honoring J. Craig Wheeler's 60th Birthday, Edited by Pawan Kumar, Craig Wheeler and Peter Hoeflich, Cambridge University Press

Abstract: We study the evolution of supernova remnants in the circumstellar medium formed by mass loss from the progenitor star. The properties of this interaction are investigated, and the specific case of a 35 $\msun$ star is studied in detail. The evolution of the SN shock wave in this case may have a bearing on other SNRs evolving in wind-blown bubbles, especially SN 1987A.

The Evolution of Supernovae in Circumstellar Wind-Blown Bubbles. I. Introduction and One-Dimensional Calculations

Vikram V Dwarkadas, 2005, ApJ

Abstract: Mass loss from massive stars (>~8 Msolar) can result in the formation of circumstellar wind-blown cavities surrounding the star, bordered by a thin, dense, cold shell. When the star explodes as a core-collapse supernova (SN), the resulting shock wave will interact with this modified medium around the star, rather than the interstellar medium. In this work we first explore the nature of the circumstellar medium around massive stars in various evolutionary stages. This is followed by a study of the evolution of SNe within these wind-blown bubbles. The evolution depends primarily on a single parameter ?, the ratio of the mass of the dense shell to that of the ejected material. We investigate the evolution for different values of this parameter. We also plot approximate X-ray surface brightness plots from the simulations. For very small values ?<<1 the effect of the shell is negligible, as one would expect. Values of ?<~1 affect the SN evolution, but the SN ``forgets'' about the existence of the shell in about 10 doubling times or so. The remnant density profile changes, and consequently the X-ray emission from the remnant will also change. The initial X-ray luminosity of the remnant is quite low, but interaction of the shock wave with the dense circumstellar shell can increase the luminosity by 2-3 orders of magnitude. As the reflected shock begins to move inward, X-ray images will show the presence of a double-shelled structure. Larger values result in more SN energy being expended to the shell. The resulting reflected shock moves quickly back to the origin, and the ejecta are thermalized rapidly. The evolution of the remnant is speeded up, and the entire remnant may appear bright in X-rays. If ?>>1, then a substantial amount of energy may be expended in the shell. In the extreme case the SN may go directly from the free expansion to the adiabatic stage, bypassing the Sedov stage. Our results show that in many cases the SNR spends a significant amount of time within the bubble. The low density within the bubble can delay the onset of the Sedov stage and may end up reducing the amount of time spent in the Sedov stage. The complicated density profile within the bubble makes it difficult to infer the mass-loss properties of the pre-SN star by studying the evolution of the resulting SNR.

Hydrodynamics of Supernova Evolution in the Winds of Massive Stars

Vikram V Dwarkadas, 2007, Astrophysics and Space Science

Abstract: Core-Collapse supernovae arise from stars greater than 8 $\msun$. These stars lose a considerable amount of mass during their lifetime, which accumulates around the star forming wind-blown bubbles. Upon the death of the star in a spectacular explosion, the resulting SN shock wave will interact with this modified medium. We study the evolution of the shock wave, and investigate the properties of this interaction. We concentrate on the evolution of the SN shock wave in the medium around a 35 solar mass star. We discuss the hydrodynamics of the resulting interaction, the formation and growth of instabilities, and deviations from sphericity.

The Evolution of Supernovae in Circumstellar Wind Bubbles II: Case of a Wolf-Rayet star

Vikram V Dwarkadas, 2007, ApJ, 667, 226

Abstract: Mass-loss from massive stars leads to the formation of circumstellar wind-blown bubbles surrounding the star, bordered by a dense shell. When the star ends its life in a supernova (SN) explosion, the resulting shock wave will interact with this modified medium. In a previous paper \citep{d05} we discussed the basic parameters of this interaction with idealized models. In this paper we go a step further and study the evolution of SNe in the wind blown bubble formed by a 35 $\msun$ star that starts off as an O star, goes through a red supergiant phase, and ends its life as a Wolf-Rayet star. We model the evolution of the circumstellar medium throughout its lifetime, and then the expansion of the SN shock wave within this medium. Our simulations clearly reveal fluctuations in density and pressure within the surrounding medium, due to the changing mass-loss parameters over the star's evolution. The SN shock interacting with these fluctuations, and then with the dense shell surrounding the wind-blown cavity, gives rise to a variety of transmitted and reflected shocks in the wind bubble. The interactions between these various shocks and discontinuities is examined, and its effects on the emission from the remnant, especially in the X-ray regime, is noted. In this particular case the shock wave is trapped in the dense shell for a large number of doubling times, and the remnant size is restricted by the size of the surrounding circumstellar bubble. Our multi-dimensional simulations reveal the presence of several hydrodynamic instabilities. They show that the turbulent interior, coupled with the large fluctuations in density and pressure, gives rise to an extremely corrugated SN shock wave. The shock shows considerable wrinkles as it impacts the dense shell, and the impact occurs in a piecemeal fashion, with some parts of the shock wave interacting with the shell before the others. As each interaction is accompanied by an increase in the X-ray and optical emission, different parts of the shell will `light-up' at different times. The reflected shock that is formed upon shell impact will comprise of several smaller shocks with different velocities, and which are not necessarily moving radially inwards. The non-spherical nature of the interaction means that it will occur over a prolonged period of time, and the spherical symmetry of the initial shock wave is completely destroyed by the end of the simulation.

Supernova propagation in the circumstellar and interstellar medium

Dwarkadas, V. V

Memorie della Societa Astronomica Italiana, v.82, p.781 (2011)

We describe the propagation of supernova shocks within the surrounding medium, which may be due to mass-loss from the progenitor star. The structure and density profile of the ejected material and surrounding medium are considered. Shock wave interaction with clouds and wind-bubbles, and issues relevant to cosmic rays are briefly discussed.

Supernova remnant evolution in wind bubbles: A closer look at Kes 27

Dwarkadas, V. V.; Dewey, D.

High Energy Density Physics, 2013, Volume 9, Issue 1, p. 22-25

Massive Stars (>8M) lose mass in the form of strong winds. These winds accumulate around the star, forming wind-blown bubbles. When the star explodes as a supernova (SN), the resulting shock wave expands within this wind-blown bubble, rather than the interstellar medium. The properties of the resulting remnant, its dynamics and kinematics, the morphology, and the resulting evolution, are shaped by the structure and properties of the wind-blown bubble. In this article we focus on Kes 27, a supernova remnant (SNR) that has been proposed by [1] to be evolving in a wind-blown bubble, explore its properties, and investigate whether the X-Ray properties could be ascribed to evolution of a SNR in a wind-blown bubble. Our initial model does not support the scenario proposed by [1], due to the fact that the reflected shock is expanding into much lower densities.