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X-ray emission is one of the signposts of circumstellar interaction in supernovae (SNe), but until now, it has been observed only in core-collapse SNe. The level of thermal X-ray emission is a direct measure of the density of the circumstellar medium (CSM), and the absence of X-ray emission from Type Ia SNe has been interpreted as a sign of a very low density CSM. In this paper, we report late-time (500-800 d after discovery) X-ray detections of SN 2012ca in Chandra data. The presence of hydrogen in the initial spectrum led to a classification of Type Ia-CSM, ostensibly making it the first SN Ia detected with X-rays. Our analysis of the X-ray data favours an asymmetric medium, with a high-density component which supplies the X-ray emission. The data suggest a number density >108 cm-3 in the higher density medium, which is consistent with the large observed Balmer decrement if it arises from collisional excitation. This is high compared to most core-collapse SNe, but it may be consistent with densities suggested for some Type IIn or superluminous SNe. If SN 2012ca is a thermonuclear SN, the large CSM density could imply clumps in the wind, or a dense torus or disc, consistent with the single-degenerate channel. A remote possibility for a core-degenerate channel involves a white dwarf merging with the degenerate core of an asymptotic giant branch star shortly before the explosion, leading to a common envelope around the SN.

We probe the environmental properties of X-ray supernova remnants (SNRs) at various points along their evolutionary journey, especially the S-T phase, and their conformance with theoretically derived models of SNR evolution. The remnant size is used as a proxy for the age of the remnant. Our data set includes 34 Milky Way, 59 Large Magellanic Cloud (LMC), and 5 Small Magellanic Cloud (SMC) SNRs. We select remnants that have been definitively typed as either core-collapse (CC) or Type Ia supernovae, with well-defined size estimates, and a thermal X-ray flux measured over the entire remnant. A catalog of SNR size and X-ray luminosity is presented and plotted, with ambient density and age estimates from the literature. Model remnants with a given density, in the Sedov-Taylor (S-T) phase, are overplotted on the diameter-versus-luminosity plot, allowing the evolutionary state and physical properties of SNRs to be compared to each other, and to theoretical models. We find that small, young remnants are predominantly Type Ia remnants or high luminosity CCs, suggesting that many CC SNRs are not detected until after they have emerged from the progenitor's wind-blown bubble. An examination of the distribution of SNR diameters in the Milky Way and LMC reveals that LMC SNRs must be evolving in an ambient medium which is 30 per cent as dense as that in the Milky Way. This is consistent with ambient density estimates for the Galaxy and LMC. [ABSTRACT FROM AUTHOR]

Core-collapse supernovae (SNe) expand into a medium created by winds from the pre-SN progenitor. The SN explosion and resulting shock wave(s) heat up the surrounding plasma, giving rise to thermal X-ray emission, which depends on the density of the emitting material. Tracking the variation of the X-ray luminosity over long periods of time thus allows for investigation of the kinematics of the SN shock waves, the structure of the surrounding medium, and the nature of the progenitor star. In this paper, X-ray observations of five of the oldest known X-ray SNe—SN 1970G, SN 1968D, SN 1959D, SN 1957D, and SN 1941C—are analyzed, with the aim of reconstructing their light curves over several decades. For those SNe for which we can extract multiepoch data, the X-ray luminosity appears to decline with time, although with large error bars. No increase in the X-ray emission from SN 1970G is found at later epochs, contrary to previous reports. All five SNe show X-ray luminosities that are of comparable magnitude. We compare the late-time X-ray luminosities of these SNe to those of supernova remnants (SNRs) in the Galaxy, which are a few hundred years old, and find that when the tentative decline is taken into account, the luminosity of the old SNe studied herein could fall below the luminosity of some of the younger SNRs within a few hundred years. However, the X-ray luminosity should begin to increase as the SNe expand in the Sedov phase, thus reaching that of the observed SNRs. [ABSTRACT FROM AUTHOR]

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 the separation of 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 ± 23 M⊙. 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. [ABSTRACT FROM AUTHOR]

Core-collapse supernovae produce fast shocks which pervade the dense circumstellar medium (CSM) of the stellar progenitor. Cosmic rays (CRs) if accelerated at these shocks can induce the growth of electromagnetic fluctuations in the foreshock medium. In this study, using a self-similar description of the shock evolution, we calculate the growth time-scales of CR-driven instabilities. We select a sample of nearby core-collapse radio supernova of type II and Ib/Ic. From radio data, we infer the parameters which enter in the calculation of the instability growth times. We find that extended IIb SNe shocks can trigger fast intra-day instabilities, strong magnetic field amplification, and CR acceleration. In particular, the non-resonant streaming instability can contribute to about 50 per cent of the magnetic field intensity deduced from radio data. This results in the acceleration of CRs in the range 1–10 PeV within a few days after the shock breakout. In order to produce strong magnetic field amplification and CR acceleration, a fast shock pervading a dense CSM is necessary. In that aspect, IIn supernovæ are also good candidates. But a detailed modelling of the blast wave dynamics coupled with particle acceleration is mandatory for this class of object before providing any firm conclusions. Finally, we find that the trans-relativistic object SN 2009bb even if it produces more modest magnetic field amplification can accelerate CRs up to 2–3 PeV within 20 d after the outburst. [ABSTRACT FROM AUTHOR]

Massive stars lose a considerable amount of mass during their lifetime. When the star explodes as a supernova (SN), the resulting shock wave expands in the medium created by the stellar mass-loss. Thermal X-ray emission from the SN depends on the square of the density of the ambient medium, which in turn depends on the mass-loss rate (and velocity) of the progenitor wind. The emission can therefore be used to probe the stellar mass-loss in the decades or centuries before the star's death. We have aggregated together data available in the literature, or analysed by us, to compute the X-ray lightcurves of almost all young supernovae detectable in X-rays. We use this database to explore the mass-loss rates of massive stars that collapse to form supernovae. Mass-loss rates are lowest for the common Type IIP supernovae, but increase by several orders of magnitude for the highest luminosity X-ray SNe. [ABSTRACT FROM AUTHOR]

Using a code that employs a self-consistent method for computing the effects of photo-ionization on circumstellar gas dynamics, we model the formation of wind-driven nebulae around massive stars. We take into account changes in stellar properties and mass-loss over the star's evolution. Our simulations show how various properties, such as the density and ionization fraction, change throughout the evolution of the star. The multi-dimensional simulations reveal the presence of strong ionization front instabilities in the main-sequence phase, similar to those seen in galactic ionization fronts. Hydrodynamic instabilities at the interfaces lead to the formation of filaments and clumps that are continually being stripped off and mixed with the low density interior. Even though the winds start out as completely radial, the spherical symmetry is quickly destroyed, and the shocked wind region is manifestly asymmetrical. The simulations demonstrate that it is important to include the effects of the photoionizing photons from the star, and simulations that do not include this may fail to reproduce the observed density profile and ionization structure of wind-blown bubbles around massive stars. [ABSTRACT FROM AUTHOR]

Massive stars, possibly red supergiants, which retain extended hydrogen envelopes until core collapse, produce Type II plateau (IIP) supernovae. The ejecta from these explosions shocks the circumstellar matter originating from the mass loss of the progenitor during the final phases of its life. This interaction accelerates particles to relativistic energies which then lose energy via synchrotron radiation in the shock-amplified magnetic fields and inverse Compton scattering against optical photons from the supernova. These processes produce different signatures in the radio and X-ray parts of the electromagnetic spectrum. Observed together, they allow us to break the degeneracy between shock acceleration and magnetic field amplification. In this work, we use X-rays observations from the Chandra and radio observations from the Australia Telescope Compact Array to study the relative importance of processes which accelerate particles and those which amplifymagnetic fields in producing the non-thermal radiation from SN 2011ja. We use radio observations to constrain the explosion date. Multiple Chandra observations allow us to probe the history of variablemass loss from the progenitor. The ejecta expands into a low-density bubble followed by interaction with a higher density wind from a red supergiant consistent with MZAMS ≳ 12M☉.Our results suggest that a fraction of Type IIP supernovae may interact with circumstellar media set up by non-steady winds. [ABSTRACT FROM AUTHOR]

Red Supergiants (RSGs) have for decades been assumed to be the progenitors of Type IIP supernovae (SNe). They are expected to have dense winds with mass-loss rates up to 10−4 M⊙ yr−1. We have created a database of available X-ray lightcurves of SNe. Type IIP SNe are found to have the lowest X-ray luminosities among all classes, which is surprising given the high mass-loss rate winds expected from their red supergiant progenitors, and therefore the high density medium into which Type IIP SNe are expected to expand into. We show that the low X-ray luminosity sets a limit on the mass-loss rate of the progenitor star which can collapse to become a RSG, which is about 10−5 M⊙ yr−1. This in turn can be used to set a limit on the initial mass of a RSG star which can become a Type IIP progenitor, which is about 19 M⊙. This is consistent with the limit obtained via direct optical progenitor identification. Optically identified progenitors of Type IIP SNe are found to be RSGs with masses less than about 17 M⊙ (Smartt (2009)). We discuss the implications of this result for stellar evolution, theorize on the fate of RSG stars with initial mass > 19 M⊙, and discuss what type of SNe they will produce at the end of their lifetime. [ABSTRACT FROM PUBLISHER]

We have aggregated together data available in the literature, or analysed by us, to compute the lightcurves of most young supernovae (SNe) that have been detected in X-rays. Currently the database contains about 60 SNe spanning all the various types, but it is expanding rapidly. We use this library of lightcurves and spectra to explore the diversity of SNe, the characteristics of the environment into which they are expanding, and the implications for their progenitors. X-ray spectra can provide insight into the density structure, composition and metallicity of the surrounding medium, and the ionization level, through the spectra themselves as well as the X-ray absorption. Since core-collapse SNe expand mainly in environments created by the progenitor star mass-loss, this can provide crucial information about the nature of the progenitor star, and its mass-loss parameters in the decades or centuries before its death. In a few cases, via detailed modelling, we can distinguish the composition of the SN ejecta from that of the environment. X-ray observations therefore provide an invaluable probe into the stellar environments of core-collapse SNe, complementing data available at other wavelengths. We provide an overview of the X-ray lightcurves of various SN types, the implications for their environment, and clues to their progenitor stars. [ABSTRACT FROM PUBLISHER]