Type Ia supernovae (SNe) are presumed to arise from white dwarf progenitors, which may not appreciably modify their ambient medium. We study the interaction of the resulting supernova remnants with a constant density interstellar medium. Density proÐles obtained from detailed explosion models of Type Ia SN explosions can be complex, but an exponential proÐle gives the best approximate representation of a set of proÐles, and we emphasize this case. We describe the time evolution of dynamical quantities (such as radius, velocity, and expansion parameter) as a result of the interaction in terms of dimensionless variables and present the proÐles of physical quantities. We compare our results to the power-law and constant ejecta density cases ; a characteristic feature of the exponential case is that the shocked ejecta have a relatively constant temperature. The e †ect of a possible circumstellar wind region close to the supernova is to create a dense, cool shell near the contact discontinuity between the shocked ejecta and the surrounding medium. The complex density structure found in some supernova models persists in the shocked layer, giving rise to density and temperature variations. We apply our results to the two likely historical Type Ia SNe, SN 1006 and Tycho. The observed angular sizes and expansion rates are consistent with a distance of 1.95^0.4 kpc and an ambient H density of 0.05È0.1 cm~3 for SN 1006. For TychoÏs SNR, the results are not conclusive but indicate a distance around 2.3 kpc for an ambient density of 0.6È1.1 cm~3. In both cases, the low expansion rate limits the extent of a possible circumstellar wind region. The evidence for temperature variations in the ejecta of TychoÏs remnant suggests that the supernova proÐle was more complex than an exponential proÐle and contained density inhomogeneities, or that there was early interaction with a circumstellar wind.
Mass loss from massive stars ( 8M ⊙ ) 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 Λ, 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 Λ << 1 the effect of the shell is negligible, as one would expect. Values of Λ 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 inwards, 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 Λ >> 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 SN remnant spends a significant amount of observed around many LBV stars (Weis
Mass-loss from massive stars leads to the formation of circumstellar windblown 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 (Dwarkadas 2005) 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 M ⊙ 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 massloss 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
Massive stars lose mass in the form of stellar winds and outbursts. This material accumulates around the star. When the star explodes as a supernova the resulting shock wave expands within this circumstellar medium. The X‐ray emission resulting from the interaction depends, among other parameters, on the density of this medium, and therefore the variation in the X‐ray luminosity can be used to study the variation in the density structure of the medium. In this paper we explore the X‐ray emission and light curves of all known supernovae (SNe), in order to study the nature of the medium into which they are expanding. In particular, we wish to investigate whether young SNe are expanding into a steady wind medium, as is most often assumed in the literature. We find that in the context of the theoretical arguments that have been generally used in the literature, many young SNe, and especially those of Type IIn SNe, which are the brightest X‐ray luminosity class, do not appear to be expanding into steady winds. Some Type IIn SNe appear to have very steep X‐ray luminosity declines, indicating density declines much steeper than r−2. However, other Type IIn SNe show a constant or even increasing X‐ray luminosity over periods of months to years. Many other SNe do not appear to have declines consistent with expansion in a steady wind. SNe with lower X‐ray luminosities appear to be more consistent with steady wind expansion, although the numbers are not large enough to make firm statistical comments. The numbers do indicate that the expansion and density structure of the circumstellar medium must be investigated before assumptions can be made of steady wind expansion. Unless a steady wind can be shown, mass‐loss rates deduced using this assumption may need to be revised.
The Type IIb supernova (SN) 1993J is one of only a few stripped-envelope supernovae with a progenitor star identified in pre-explosion images. SN IIb models typically invoke H envelope stripping by mass transfer in a binary system. For the case of SN 1993J, the models suggest that the companion grew to 22 M ⊙ and became a source of ultraviolet (UV) excess. Located in M81, at a distance of only 3.6 Mpc, SN 1993J offers one of the best opportunities to detect the putative companion and test the progenitor model. Previously published near-UV spectra in 2004 showed evidence for absorption lines consistent with a hot (B2 Ia) star, but the field was crowded and dominated by flux from the SN. Here we present Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) and Wide-Field Camera 3 (WFC3) observations of SN 1993J from 2012, at which point the flux from the SN had faded sufficiently to potentially measure the UV continuum properties from the putative companion. The resulting UV spectrum is consistent with contributions from both a hot B star and the SN, although we cannot rule out line-of-sight coincidences.
We present optical photometric and spectroscopic observations of supernova 2013ej. It is one of the brightest type II supernovae exploded in a nearby (∼ 10 Mpc) galaxy NGC 628. The light curve characteristics are similar to type II SNe, but with a relatively shorter (∼ 85 day) and steeper (∼ 1.7 mag (100 d) −1 in V ) plateau phase. The SN shows a large drop of 2.4 mag in V band brightness during plateau to nebular transition. The absolute ultraviolet (UV) light curves are identical to SN 2012aw, showing a similar UV plateau trend extending up to 85 days. The radioactive 56 Ni mass estimated from the tail luminosity is 0.02M ⊙ which is significantly lower than typical type IIP SNe. The characteristics of spectral features and evolution of line velocities indicate that SN 2013ej is a type II event. However, light curve characteristics and some spectroscopic features provide strong support in classifying it as a type IIL event. A detailed synow modelling of spectra indicates the presence of some high velocity components in Hα and Hβ profiles, implying possible ejecta-CSM interaction. The nebular phase spectrum shows an unusual notch in the Hα emission which may indicate bipolar distribution of 56 Ni. Modelling of the bolometric light curve yields a progenitor mass of ∼ 14M ⊙ and a radius of ∼ 450R ⊙ , with a total explosion energy of ∼ 2.3 × 10 51 erg.
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