Type II Supernovae & SN 1987A Research

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The presupernova HII region around SN1987A -Roger A. Chevalier & Vikram V. Dwarkadas. ApJL. 452, L45, 1995

Abstract: The slow expansion of the bright ring around SN 1987A and the large size estimated for the radio source at an age of ~1500 days suggest a low mass-loss rate, M dot , from the blue supergiant progenitor star; we adopt M dot = 7.5 x 10-8 M&sun; yr-1 and a wind velocity vw = 450 km s-1 as standard values. This wind density would not give substantial radio free-free absorption during the first few days when low-frequency absorption was observed, but the turnover can be attributed to synchrotron self-absorption. The X-ray and radio emission observed since 1990 require that the supernova shock be interacting with denser gas than that in the free wind. We propose that it is interacting with an H II region created by the B3 Ia progenitor star in the swept-up red supergiant wind. The H II region extends from a radius rII ~ 3 x 1017 cm to the ring radius R = 6 x 1017 cm in the equatorial plane and has a hydrogen density ~102 cm-3. The shock front will not reach the dense ring until the year 2005 +/- 3. The X-ray luminosity should slowly increase until that time. The equatorial ionization front is trapped in the swept-up gas; the dense ring and its associated bipolar nebula are the initially neutral part of the shell. In the polar direction, the ionization front broke out of the swept-up gas, and there is no dense neutral shell, consistent with the observed lack of a thin shell in that direction.

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.

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 M_{sun}), 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.

Supernova Explosions in Winds and Bubbles, with Applications to SN 1987A V. V. Dwarkadas, 2007, to be published in the proceedings of the conference "Circumstellar Media and Late Stages of Massive Stellar Evolution" held in Ensenada, Mexico

Abstract: Massive stars can significantly modify the surrounding medium during their lifetime. When the stars explode as supernovae, the resulting shock wave expands within this modified medium and not within the interstellar medium. We explore the evolution of the medium around massive stars, and the expansion of the shock wave within this medium. We then apply these results to understanding the expansion of the shock wave in the ambient medium surrounding SN 1987A, and the evolution of the radio and X-ray emission in this case.

SN Shock Evolution in the Circumstellar Medium surrounding SN 1987A V. V. Dwarkadas, 2007, To be published in the proceedings of the conference on "Supernova 1987A: 20 Years After: Supernovae and Gamma-Ray Bursters" AIP, New York, eds. S. Immler, K.W. Weiler, and R. McCray

Abstract: We study the structure of the circumstellar medium surrounding SN 1987A in the equatorial plane. Furthermore, we study the evolution of the SN shock within this medium during the first 25 years, and the resulting hard X-ray and radio emission from the remnant.

Type II Supernovae & SN 1987A Research

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