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The structure and evolution of wind-blown bubbles (WBBs) around massive stars has primarily been investigated using an energy-conserving model of wind-blown bubbles. While this model is useful in explaining the general properties of the evolution, several problems remain, including inconsistencies between observed wind luminosities and those derived using this formulation. Major difficulties include the low X-ray temperature and X-ray luminosity, compared to the model. In this paper, we re-examine the evolution, dynamics, and kinematics of WBBs around massive stars, using published ionization gasdynamic simulations of wind-blown bubbles. We show that WBBs can cool efficiently due to the presence of various instabilities and turbulence within the bubble. The expansion of WBBs is more consistent with a momentum-conserving solution, rather than an energy-conserving solution. This compares well with the dynamics and kinematics of observed wind bubbles. Despite the cooling of the bubble, the shocked wind temperature is not reduced to the observed values. We argue that the X-ray emission arise mainly from clumps and filaments within the hot shocked wind region, with temperatures just above 10$^6$ K. The remainder of the plasma can contribute to a lesser extent., Comment: 22 pages, 7 figures. Published in Galaxies. Only low-resolution figures are included due to size requirements; original high-resolution figures, especially Figure 1, can be obtained from the published paper in the journal

I report on Chandra X-ray observations of SN 2018cqj, a low luminosity Type Ia supernova that showed an H$\alpha$ line in its optical spectrum. No X-ray emission was detected at the location of the SN, with an upper limit to the X-ray luminosity of 2 $\times 10^{39}$ erg s$^{-1}$., Comment: 3 pages, 1 table. Published in RNAAS

We analyze the X-Ray emission from the supernova remnant DEM L71 using the Smoothed Particle Inference (SPI) technique. The high Fe abundance found appears to confirm the Type Ia origin. Our method allows us to separate the material ejected in the supernova explosion from the material swept-up by the supernova shock wave. We are able to calculate the total mass of this swept-up material to be about 228 $\pm$ 23 M$_{\odot}$. We plot the posterior distribution for the number density parameter, and create a map of the density structure within the remnant. While the observed density shows substantial variations, we find our results are generally consistent with a two-dimensional hydrodynamical model of the remnant that we have run. Assuming the ejected material arises from a Type Ia explosion, with no hydrogen present, we use the predicted yields from Type Ia models available in the literature to characterize the emitting gas. We find that the abundance of various elements match those predicted by deflagration to detonation transition (DDT) models. Our results, compatible with the Type Ia scenario, highlight the complexity of the remnant and the nature of the surrounding medium., Comment: 6 pages, 7 Figures. Accepted for publication in Astronomische Nachrichten. To appear as part of the Proceedings of the XMM-Newton 2019 Workshop on "Astrophysics of Hot Plasma in Extended X-Ray Sources"

There is now solid experimental evidence of at least one supernova explosion within 100 pc of Earth within the last few million years, from measurements of the short-lived isotope 60Fe in widespread deep-ocean samples, as well as in the lunar regolith and cosmic rays. This is the first established example of a specific dated astrophysical event outside the Solar System having a measurable impact on the Earth, offering new probes of stellar evolution, nuclear astrophysics, the astrophysics of the solar neighborhood, cosmic-ray sources and acceleration, multi-messenger astronomy, and astrobiology. Interdisciplinary connections reach broadly to include heliophysics, geology, and evolutionary biology. Objectives for the future include pinning down the nature and location of the established near-Earth supernova explosions, seeking evidence for others, and searching for other short-lived isotopes such as 26Al and 244Pu. The unique information provided by geological and lunar detections of radioactive 60Fe to assess nearby supernova explosions make now a compelling time for the astronomy community to advocate for supporting multi-disciplinary, cross-cutting research programs., Comment: 11 pages, 2 figures. Astro2020 Science White Paper submitted to the 2020 Decadal Survey on Astronomy and Astrophysics

The progenitors of Type IIP supernovae (SNe) are known to be red supergiants, but their properties are not well determined. We employ hydrodynamical modelling to investigate the explosion characteristics of eight Type IIP supernovae, and the properties of their progenitor stars. We create evolutionary models using the {\sc MESA} stellar evolution code, explode these models, and simulate the optical lightcurves using the {\sc STELLA} code. We fit the optical lightcurves, Fe II 5169\AA\ velocity, and photospheric velocity, to the observational data. Recent research has suggested that the progenitors of Type IIP SNe have a zero age main sequence (ZAMS) mass not exceeding $\sim18$ M$_{\odot}$. Our fits give a progenitor ZAMS mass $\leq18$ M$_{\odot}$ for seven of the supernovae. Where previous progenitor mass estimates exist, from various sources such as hydrodynamical modelling, multi-wavelength observations, or semi-analytic calculations, our modelling generally tends towards the lower mass values. This result is in contrast to results from previous hydrodynamical modelling, but is consistent with those obtained using general-relativistic radiation-hydrodynamical codes. We do find that one event, SN 2015ba, has a progenitor whose mass is closer to 24 M$_{\odot}$ , although we are unable to fit it well. We also derive the amount of $^{56}$Ni required to reproduce the tail of the lightcurve, and find values generally larger than previous estimates. Overall, we find that it is difficult to characterize the explosion by a single parameter, and that a range of parameters is needed., Comment: 21 pages, 16 figures. Accepted to the Astrophysical Journal

A range of astronomical data indicates that ancient supernovae created the galactic environment of the Sun and sculpted the physical properties of the interstellar medium near the heliosphere. In this paper we review the characteristics of the local interstellar medium that have been affected by supernovae. The kinematics, magnetic field, elemental abundances, and configuration of the nearest interstellar material support the view that the Sun is at the edge of the Loop I superbubble, which has merged into the low density Local Bubble. The energy source for the higher temperature X-ray emitting plasma pervading the Local Bubble is uncertain. Winds from massive stars and nearby supernovae, perhaps from the Sco-Cen Association, may have contributed radioisotopes found in the geologic record and galactic cosmic ray population. Nested supernova shells in the Orion and Sco-Cen regions suggest spatially distinct sites of episodic star formation. The heliosphere properties vary with the pressure of the surrounding interstellar cloud. A nearby supernova would modify this pressure equilibrium and thereby severely disrupt the heliosphere as well as the local interstellar medium., Comment: 30 pages, 7 figures. Author version, updated and modified (several updated and new paragraphs, one new subsection), of an article that was published in the Handbook of Supernovae, A.W. Alsabti, P. Murdin (eds.), Springer, 2016

Using a code that employs a self-consistent method for computing the effects of photoionization on circumstellar gas dynamics, we model the formation of wind-driven nebulae around massive Wolf-Rayet (W-R) stars. Our algorithm incorporates a simplified model of the photo-ionization source, computes the fractional ionization of hydrogen due to the photoionizing flux and recombination, and determines self-consistently the energy balance due to ionization, photo-heating and radiative cooling. We take into account changes in stellar properties and mass-loss over the star's evolution. Our multi-dimensional simulations clearly reveal the presence of strong ionization front instabilities. Using various X-ray emission models, and abundances consistent with those derived for W-R nebulae, we compute the X-ray flux and spectra from our wind bubble models. We show the evolution of the X-ray spectral features with time over the evolution of the star, taking the absorption of the X-rays by the ionized bubble into account. Our simulated X-ray spectra compare reasonably well with observed spectra of Wolf-Rayet bubbles. They suggest that X-ray nebulae around massive stars may not be easily detectable, consistent with observations., 3 pages, 4 figures. To be published in the Proceedings of the International Workshop on Wolf-Rayet Stars, Potsdam, 1-5 June 2015. Editors W.-R. Hamann, A. Sander, and H. Todt

We present calculations of the radio images and light curves from supernovae, based on high-resolution numerical simulations of the hydrodynamics and radiation transfer in a spherically symmetric medium. As a specific example we model the emission from SN1993J. This supernova does not appear to be expanding in a self-similar fashion, and cannot be adequately fitted with the often-used analytic mini-shell model. We present a good fit to the radio evolution at a single frequency. Both free-free absorption and synchrotron self-absorption are needed to fit the light curve at early times, and a circumstellar density profile of $\rho \sim r ^{-1.7}$ provides the best fit to the later data. Comparisons of VLBI images of SN1993J with synthetic model images suggest that internal free-free absorption completely obscures emission at 8.4 GHz passing through the center of the supernova for the first few tens of years after explosion., Comment: 5 pages, 4 figures, to appear in proceedings of IAU Colloq. 192, Supernovae: 10 Years of 1993J, eds. J.M. Marcaide and K.W. Weiler, Springer Verlag

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 (SN) 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 lightcurves of all known 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, which are the brightest X-ray luminosity class, do not appear to be expanding into steady winds. Some IIns appear to have very steep X-ray luminosity declines, indicating density declines much steeper than r$^{-2}$. However, other IIns 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., 12 pages, 3 color Figures. Accepted to MNRAS

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., 6 pages, 3 figures. Final version, minor changes. Invited review presented at the conference on Cosmic Rays and the Interstellar Medium (CRISM-2011), Montpellier, France, June 26-July 1. Published in a special issue of MEMORIE della Societa Astronomica Italiana

Luminous blue variable (LBV) stars are very massive, luminous, unstable stars that suffer frequent eruptions. In the last few years, these stars have been proposed as the direct progenitors of some core-collapse supernovae (SNe), particularly Type IIn SNe, in conflict with stellar evolution theory. In this paper we investigate various scenarios wherein LBV stars have been suggested as the immediate progenitors of SNe. Many of these suggestions stem from the fact that the SNe appear to be expanding in a high density medium, which has been interpreted as resulting from a wind with a high mass-loss rate. Others arise due to perceived similarities between the SN characteristics and those of LBVs. Only in the case of SN 2005gl do we find a valid possibility for an LBV-like progenitor. Other scenarios encounter various levels of difficulty. The evidence that points to LBVs as direct core-collapse SNe progenitors is far from convincing. High mass-loss rates are often deduced by making assumptions regarding the wind parameters, which are contradicted by the results themselves. A high density need not necessarily imply a high wind mass-loss rate: wind shocks sweeping up the surrounding medium may give a high density shell with a low associated wind mass-loss rate. High densities may also arise due to wind clumps, or due to a previous LBV phase before the SN explodes as a Wolf-Rayet star. Some Type IIn SNe appear to signify more a phase in the life of a SN than a class of SNe, and may arise from more than one type of progenitor. A Wolf-Rayet phase that lasts for a few thousand years or less could be one of the more probable progenitors of Type IIns, and channels for creating short-lived W-R phases are briefly discussed., Comment: Accepted to MNRAS. 13 pages, 1 figure

SN1996cr is one of the five closest SNe to explode in the past 30 years. Due to its fortuitous location in the Circinus Galaxy at ~ 3.7 Mpc, there is a wealth of recently acquired and serendipitous archival data available to piece together its evolution over the past decade, including a recent 485 ks Chandra HETG spectrum. In order to interpret this data, we have explored hydrodynamic simulations, followed by computations of simulated spectra and light curves under non-equilibrium ionization conditions, and directly compared them to the observations. Our simulated spectra manage to fit both the X-ray continuum and lines at 4 epochs satisfactorily, while our computed light curves are in good agreement with additional flux-monitoring data sets. These calculations allow us to infer the nature and structure of the circumstellar medium, the evolution of the SN shock wave, and the abundances of the ejecta and surrounding medium. The data imply that SN 1996cr exploded in a low-density medium before interacting with a dense shell of material about 0.03pc away from the progenitor star. We speculate that the shell could be due to the interaction of a blue supergiant or Wolf-Rayet wind with a previously existing red supergiant (RSG) wind. The shock wave has now exited the shell and is expanding in the medium exterior to it, possibly the undisturbed continuation of the dense RSG wind. The narrow lines that earned SN 1996cr its IIn designation possibly arise from dense, shocked clumps in the CSM. Although the possibility for an LBV progenitor for this Type IIn SN cannot be completely excluded, it is inconsistent with much of the data. These calculations allow us to probe the stellar mass loss in the very last phases ($ < 10^4$ years) of a massive star's life ($> 10^6$ years), and provide another means to deducing the progenitor of the SN., Accepted to MNRAS. 21 pages, 8 Figures, 6 in color. For a version with higher resolution colour figures see http://astro.uchicago.edu/~vikram/1996cr/

We present a comprehensive analysis of the X-ray light curves of SN 1993J in a nearby galaxy M81. This is the only supernova other than SN 1987A, which is so extensively followed in the X-ray bands. Here we report on SN 1993J observations with the {\it Chandra} in the year 2005 and 2008, and Swift observations in 2005, 2006 and 2008. We combined these observations with all available archival data of SN 1993J, which includes ROSAT, ASCA, {\it Chandra}, and XMM-{\it Newton} observations from 1993 April to 2006 August. In this paper we report the X-ray light curves of SN 1993J, extending up to fifteen years, in the soft (0.3--2.4 keV), hard (2--8 keV) and combined (0.3--8 keV) bands. The hard and soft-band fluxes decline at different rates initially, but after about 5 years they both undergo a $t^{-1}$ decline. The soft X-rays, which are initially low, start dominating after a few hundred days. We interpret that most of the emission below 8 keV is coming from the reverse shock which is radiative initially for around first 1000-2000 days and then turn into adiabatic shock. Our hydrodynamic simulation also confirms the reverse shock origin of the observed light curves. We also compare the H$\alpha$ line luminosity of SN 1993J with its X-ray light curve and note that the H$\alpha$ line luminosity has a fairly high fraction of the X-ray emission, indicating presence of clumps in the emitting plasma., Comment: 33 pages, 8 figures, Accepted for publication in Astrophysical Journal

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., Comment: 8 pages, 5 figues. To appear in RMxAA, as part of the proceedings of the conference "Circumstellar Media and Late Stages of Massive Stellar Evolution" held in Ensenada, Mexico, Sept 2006. A version with higher resolution figures is available at http://astro.uchicago.edu/~vikram/bubbles_87a.pdf

We illustrate how rotation of the central star can give rise to latitudinal variations in the wind properties from the star. Interaction of these winds with the surrounding medium can produce asymmetrical planetary nebulae., 4 pages; to appear in Asymmetric Planetary Nebulae III, eds. M. Meixner, J. Kastner, N.Soker and B. Balick (ASP Conf. Ser.)

The evolution of Type Ia supernovae in the surrounding medium is studied using 2-dimensional numerical hydrodynamic simulations. The ejecta are assumed to be described by an exponential density profile, following the work of Dwarkadas & Chevalier (1998). The case of a circumstellar (CS) region formed by mass loss from the progenitor or a companion star is also considered. The decelerating contact discontinuity is found to be Rayleigh-Taylor (R-T) unstable, as expected, and the nature of the instability is studied in detail for 2 cases: 1) a constant density ambient medium, and 2) a CS medium whose density goes as r^{-2}. The nature of the instability is found to be different in both cases. In the case of a CS medium the instability is much better resolved, and a fractal-like structure is seen. In the case of a constant density medium the extent of growth is less, and the R-T fingers are found to be limited by the presence of Kelvin-Helmholtz mushroom caps at the tips of the fingers. The unstable region is far enough away from the reverse shock that the latter is not affected by the mixing taking place in the interaction region. In contrast the reverse shock in the case of a CS medium is found to be rippled due to the formation of instabilities. In neither case is the outer shock front affected. These results are consistent with similar studies of power-law ejecta profiles conducted by Chevalier, Blondin & Emmering (1992). Our results are then applied to Tycho's supernova remnant., Latex manuscript, 7 postscript figures. To be published in the Astrophysical Journal, Sept 20 2000. Colour versions of the b/w figures may be obtained from the author (vikram@physics.usyd.edu.au)