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Cassiopeia A (Cas A) is one of the best studied young Galactic supernova remnants. While it provides a rare opportunity to study in detail the remnant of a supernova (SN) type IIb, questions remain regarding the nature of its progenitor, its mass-loss history, and its pre-SN evolution. Here we present an optical investigation of the circumstellar environment around Cas A and find clumpy and filamentary Hα emission nebulosities concentrated 10–15 pc (10′–15′) to the north and east. First reported by Minkowski as a faint H ii region, these nebulosities exhibit distinct morphological and spectroscopic properties relative to the surrounding diffuse emissions. Compared to neighboring H ii regions, these nebulae show stronger [N ii] 6548, 6583 Å and [S ii] 6716, 6731 Å emissions relative to Hα. We show that Cas A’s highest-velocity ejecta knots are interacting with some of the closest projected emission nebulae, thus providing strong evidence that these nebulae lie at the same distance as the remnant. We interpret these surrounding nebulosities to be the remains of the progenitor’s red supergiant wind, which accumulated against the southern edge of a large extended H ii region located north of Cas A. Our findings are consistent with the view that Cas A’s progenitor underwent considerable mass loss, first from a fast main-sequence wind, then from a slower, clumpy red supergiant wind, and finally from a brief high-velocity wind, like that from a yellow supergiant. [ABSTRACT FROM AUTHOR]

We measure the expansion of the forward shock of the Small Magellanic Cloud supernova remnant 1E 0102.2–7219 in X-rays using Chandra X-Ray Observatory on-axis Advanced CCD Imaging Spectrometer observations from 1999 to 2016. We estimate an expansion rate of 0.025% ± 0.006% yr−1 and a blast wave velocity of . Assuming partial electron–ion equilibration via Coulomb collisions and cooling due to adiabatic expansion, this velocity implies a post-shock electron temperature of 0.84 ± 0.20 keV, which is consistent with the estimate of 0.68 ± 0.05 keV based on the X-ray spectral analysis. We combine the expansion rate with the blast wave and reverse shock radii to generate a grid of one-dimensional models for a range of ejecta masses () to constrain the explosion energy, age, circumstellar density, swept-up mass, and unshocked-ejecta mass. We find acceptable solutions for a constant-density ambient medium and for an r−2 power-law profile (appropriate for a constant progenitor stellar wind). For the constant-density case, we find an age of ∼1700 yr, explosion energies (0.87–2.61) × 1051 erg, ambient densities 0.85–2.54 amu cm−3, swept-up masses , and unshocked-ejecta masses . For the power-law density profile, we find an age of ∼2600 yr, explosion energies (0.34–1.02) × 1051 erg, densities at the blast wave, swept-up masses , and unshocked-ejecta masses . Assuming that the true explosion energy was (0.5–1.5) × 1051 erg, ejecta masses are favored for the constant-density case and for the power-law case. The unshocked-ejecta mass estimates are comparable to Fe masses expected in core-collapse supernovae with progenitor mass , offering a possible explanation for the lack of Fe emission observed in X-rays. [ABSTRACT FROM AUTHOR]

Type Ia supernovae originate from the explosion of carbon–oxygen white dwarfs in binary systems, but the exact nature of their progenitors remains elusive. The bulk properties of Type Ia supernova remnants, such as the radius and the centroid energy of the Fe Kα blend in the X-ray spectrum, are determined by the properties of the supernova ejecta and the ambient medium. We model the interaction between Chandrasekhar and sub-Chandrasekhar models for Type Ia supernova ejecta and a range of uniform ambient medium densities in one dimension up to an age of 5000 years. We generate synthetic X-ray spectra from these supernova remnant models and compare their bulk properties at different expansion ages with X-ray observations from Chandra and Suzaku. We find that our models can successfully reproduce the bulk properties of most observed remnants, suggesting that Type Ia SN progenitors do not modify their surroundings significantly on scales of a few pc, although more detailed models are required to establish quantitative limits on the density of any such surrounding circumstellar material. Ambient medium density and expansion age are the main contributors to the diversity of the bulk properties in our models. Chandrasekhar and sub-Chandrasekhar progenitors make similar predictions for the bulk remnant properties, but detailed fits to X-ray spectra have the power to discriminate explosion energetics and progenitor scenarios. [ABSTRACT FROM AUTHOR]

There is now substantial evidence that the progenitors of some core-collapse supernovae undergo enhanced or extreme mass loss prior to explosion. The imprint of this mass loss is observed in the spectra and dynamics of the expanding blast wave on timescales of days to years after core collapse, and the effects on the spectral and dynamical evolution may linger long after the supernova has evolved into the remnant stage. In this paper, we present, for the first time, largely self-consistent end-to-end simulations for the evolution of a massive star from the pre-main sequence, up to and through core collapse, and into the remnant phase. We present three models and compare and contrast how the progenitor mass-loss history impacts the dynamics and spectral evolution of the supernovae and supernova remnants. We study a model that only includes steady mass loss, a model with enhanced mass loss over a period of ∼5000 yr prior to core collapse, and a model with extreme mass loss over a period of ∼500 yr prior to core collapse. The models are not meant to address any particular supernova or supernova remnant, but rather to highlight the important role that the progenitor evolution plays in the observable qualities of supernovae and supernova remnants. Through comparisons of these three different progenitor evolution scenarios, we find that the mass loss in late stages (during and after core carbon burning) can have a profound impact on the dynamics and spectral evolution of the supernova remnant centuries after core collapse. [ABSTRACT FROM AUTHOR]

The progenitor systems of the class of “Ca-rich transients” is a key open issue in time domain astrophysics. These intriguing objects exhibit unusually strong calcium line emissions months after explosion, fall within an intermediate luminosity range, are often found at large projected distances from their host galaxies, and may play a vital role in enriching galaxies and the intergalactic medium. Here we present multiwavelength observations of iPTF15eqv in NGC 3430, which exhibits a unique combination of properties that bridge those observed in Ca-rich transients and SNe Ib/c. iPTF15eqv has among the highest [Ca ii]/[O i] emission line ratios observed to date, yet is more luminous and decays more slowly than other Ca-rich transients. Optical and near-infrared photometry and spectroscopy reveal signatures consistent with the supernova explosion of a star that was stripped of its H-rich envelope via binary interaction. Distinct chemical abundances and ejecta kinematics suggest that the core collapse occurred through electron-capture processes. Deep limits on possible radio emission made with the Jansky Very Large Array imply a clean environment (n ≲ 0.1 cm−3) within a radius of cm. Chandra X-ray Observatory observations rule out alternative scenarios involving the tidal disruption of a white dwarf (WD) by a black hole, for masses >100 M⊙. Our results challenge the notion that spectroscopically classified Ca-rich transients only originate from WD progenitor systems, complicate the view that they are all associated with large ejection velocities, and indicate that their chemical abundances may vary widely between events. [ABSTRACT FROM AUTHOR]

We report on the proper motions of Balmer-dominated filaments in Kepler’s supernova remnant using high resolution images obtained with the Hubble Space Telescope at two epochs separated by about 10 years. We use the improved proper motion measurements and revised values of shock velocities to derive a distance to Kepler of kpc. The main shock around the northern rim of the remnant has a typical speed of 1690 km s−1 and is encountering material with densities of about 8 cm−3. We find evidence for the variation of shock properties over small spatial scales, including differences in the driving pressures as the shock wraps around a curved cloud surface. We find that the Balmer filaments ahead of the ejecta knot on the northwest boundary of the remnant are becoming fainter and more diffuse. We also find that the Balmer filaments associated with circumstellar material in the interior regions of the remnant are due to shocks with significantly lower velocities and that the brightness variations among these filaments trace the density distribution of the material, which may have a disk-like geometry. [ABSTRACT FROM AUTHOR]

Recent observations by the Large Area Telescope on board the Fermi satellite have revealed bright γ-ray emission from middle-aged supernova remnants (SNRs) inside our Galaxy. These remnants, which also possess bright non-thermal radio shells, are often found to be interacting directly with surrounding gas clouds. We explore the non-thermal emission mechanism at these dynamically evolved SNRs by constructing a hydrodynamical model. Two scenarios of particle acceleration, either a re-acceleration of Galactic cosmic rays or an efficient nonlinear diffusive shock acceleration (NLDSA) of particles injected from downstream, are considered. Using parameters inferred from observations, our models are contrasted with the observed spectra of SNR W44. For the re-acceleration case, we predict a significant enhancement of radio and GeV emission as the SNR undergoes a transition into the radiative phase. If sufficiently strong magnetic turbulence is present in the molecular cloud, the re-acceleration scenario can explain the observed broadband spectral properties. The NLDSA scenario also succeeds in explaining the γ-ray spectrum but fails to reproduce the radio spectral index. Efficient NLDSA also results in a significant post-shock non-thermal pressure that limits the compression during cooling and prevents the formation of a prominent dense shell. Some other interesting differences between the two models in hydrodynamical behavior and resulting spectral features are illustrated. [ABSTRACT FROM AUTHOR]

The recent discovery that the Fe–K line luminosities and energy centroids observed in nearby supernova remnants are a strong discriminant of both progenitor type and circumstellar environment has implications for our understanding of supernova progenitor evolution. Using models for the chemical composition of core-collapse supernova (CCSN) ejecta, we model the dynamics and thermal X-ray emission from shocked ejecta and circumstellar material, modeled as an wind, to ages of 3000 yr. We compare the X-ray spectra expected from these models to observations made with the Suzaku satellite. We also model the dynamics and X-ray emission from Type Ia progenitor models. We find a clear distinction in Fe–K line energy centroid between core-collapse and Type Ia models. The CCSN models predict higher Fe–K line centroid energies than the Type Ia models, in agreement with observations. We argue that the higher line centroids are a consequence of the increased densities found in the circumstellar environment created by the expansion of the slow-moving wind from the massive progenitors. [ABSTRACT FROM AUTHOR]