The Three-Dimensional Structure of Interior Ejecta in Cassiopeia A at High Spectral Resolution
TL;DR: In this paper, the authors used the Spitzer Space Telescope's Infrared Spectrograph to create a high resolution spectral map of the central region of the Cassiopeia A supernova remnant, allowing them to make a Doppler reconstruction of its 3D structure.
Abstract: We used the Spitzer Space Telescope's Infrared Spectrograph to create a high resolution spectral map of the central region of the Cassiopeia A supernova remnant, allowing us to make a Doppler reconstruction of its 3D structure. The ejecta responsible for this emission have not yet encountered the remnant's reverse shock or the circumstellar medium, making it an ideal laboratory for exploring the dynamics of the supernova explosion itself. We observe that the O, Si, and S ejecta can form both sheet-like structures as well as filaments. Si and O, which come from different nucleosynthetic layers of the star, are observed to be coincident in velocity space in some regions, and separated by 500 km/s or more in others. Ejecta traveling toward us are, on average, ~900 km/s slower than the material traveling away from us. We compare our observations to recent supernova explosion models and find that no single model can simultaneously reproduce all the observed features. However, models of different supernova explosions can collectively produce the observed geometries and structures of the interior emission. We use the results from the models to address the conditions during the supernova explosion, concentrating on asymmetries in the shock structure. We also predict that the back surface of Cassiopeia A will begin brightening in ~30 years, and the front surface in ~100 years.
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TL;DR: In this paper, the authors present 3D simulations of supernova explosions of nonrotating stars, triggered by the delayed neutrino-heating mechanism with a suitable choice of the core-neutrino luminosity.
Abstract: We present three-dimensional (3D) simulations of supernova explosions of nonrotating stars, triggered by the delayed neutrino-heating mechanism with a suitable choice of the core-neutrino luminosity. Our results show that asymmetric mass ejection caused by hydrodynamic instabilities can accelerate the neutron star (NS) up to recoil velocities of more than 700 km s-1 by the “gravitational tug-boat mechanism”, which is sufficient to explain most observed pulsar space velocities. The associated NS spin periods for our nonrotating progenitors are about 100 ms to 8000 ms without any obvious correlation between spin and kick magnitudes or directions. This suggests that faster spins and a possible spin-kick alignment might require angular momentum in the progenitor core prior to collapse. Our simulations for the first time demonstrate a clear correlation between the size of the NS kick and anisotropic production and distribution of heavy elements created by explosive burning behind the shock. In the case of large pulsar kicks, the explosion is significantly stronger opposite to the kick vector. Therefore the bulk of the explosively fused iron-group elements, in particular nickel, are ejected mostly in large clumps against the kick direction. This contrasts with the case of low recoil velocity, where the nickel-rich lumps are more isotropically distributed. Explosively produced intermediate-mass nuclei heavier than 28 Si (like 40 Ca and 44 Ti) also exhibit significant enhancement in the hemisphere opposite to the direction of fast NS motion, while the distribution of 12 C, 16 O, and 20 Ne is not affected, and that of 24 Mg only marginally. Mapping the spatial distribution of the heavy elements in supernova remnants with identified pulsar motion may offer an important diagnostic test of the kick mechanism. Unlike kick scenarios based on anisotropic neutrino emission, our hydrodynamical acceleration model predicts enhanced ejection of iron-group elements and of their nuclear precursors in the opposite direction to the NS recoil.
266 citations
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...2-0.3 (Moon et al. 2009), and Cassiopeia A (Isensee et al. 2010; DeLaney et al. 2010; Rest et al. 2011; Hwang & Laming 2012) in different wavebands may offer a promising perspective....
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...The SN remnants Cassiopeia A (Isensee et al. 2010; DeLaney et al. 2010; Rest et al. 2011; Hwang & Laming 2012) and Puppis A (Petre et al. 1996; Winkler & Petre 2007; Katsuda et al. 2008, 2010; Becker et al. 2012) may be such lucky cases, because in the former all the SN ejecta in the remnant, whose…...
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California Institute of Technology1, University of California, Berkeley2, North Carolina State University3, Los Alamos National Laboratory4, Goddard Space Flight Center5, University of Texas at Arlington6, Durham University7, McGill University8, University of Toulouse9, Hoffmann-La Roche10, Technical University of Denmark11, Lawrence Livermore National Laboratory12, Agenzia Spaziale Italiana13, Columbia University14, SLAC National Accelerator Laboratory15, INAF16
TL;DR: The observed spatial distribution rules out symmetric explosions even with a high level of convective mixing, as well as highly asymmetric bipolar explosions resulting from a fast-rotating progenitor, providing strong evidence for the development of low-mode convective instabilities in core-collapse supernovae.
Abstract: Asymmetry is required by most numerical simulations of stellar core-collapse explosions, but the form it takes differs significantly among models. The spatial distribution of radioactive ^(44)Ti, synthesized in an exploding star near the boundary between material falling back onto the collapsing core and that ejected into the surrounding medium, directly probes the explosion asymmetries. Cassiopeia A is a young, nearby, core-collapse remnant from which ^(44)Ti emission has previously been detected but not imaged. Asymmetries in the explosion have been indirectly inferred from a high ratio of observed ^(44)Ti emission to estimated ^(56)Ni emission, from optical light echoes, and from jet-like features seen in the X-ray and optical ejecta. Here we report spatial maps and spectral properties of the ^(44)Ti in Cassiopeia A. This may explain the unexpected lack of correlation between the ^(44)Ti and iron X-ray emission, the latter being visible only in shock-heated material. The observed spatial distribution rules out symmetric explosions even with a high level of convective mixing, as well as highly asymmetric bipolar explosions resulting from a fast-rotating progenitor. Instead, these observations provide strong evidence for the development of low-mode convective instabilities in core-collapse supernovae.
262 citations
TL;DR: In this article, the authors provide a set of stellar evolution and nucleosynthesis calculations that apply established physics assumptions simultaneously to low and intermediate-mass and massive star models, and provide an internally consistent and comprehensive nuclear production and yield database for applications in areas such as presolar grain studies.
Abstract: We provide a set of stellar evolution and nucleosynthesis calculations that applies established physics assumptions simultaneously to low- and intermediate-mass and massive star models. Our goal is to provide an internally consistent and comprehensive nuclear production and yield database for applications in areas such as presolar grain studies. Our non-rotating models assume convective boundary mixing (CBM) where it has been adopted before. We include 8 (12) initial masses for Z = 0.01 (0.02). Models are followed either until the end of the asymptotic giant branch phase or the end of Si burning, complemented by simple analytic core-collapse supernova (SN) models with two options for fallback and shock velocities. The explosions show which pre-SN yields will most strongly be effected by the explosive nucleosynthesis. We discuss how these two explosion parameters impact the light elements and the s and p process. For low- and intermediate-mass models, our stellar yields from H to Bi include the effect of CBM at the He-intershell boundaries and the stellar evolution feedback of the mixing process that produces the ${}^{13}{\rm{C}}$ pocket. All post-processing nucleosynthesis calculations use the same nuclear reaction rate network and nuclear physics input. We provide a discussion of the nuclear production across the entire mass range organized by element group. The entirety of our stellar nucleosynthesis profile and time evolution output are available electronically, and tools to explore the data on the NuGrid VOspace hosted by the Canadian Astronomical Data Centre are introduced.
215 citations
Cites background from "The Three-Dimensional Structure of ..."
...…Busso et al. 2001; Garćıa-Hernández et al. 2006; Hernandez et al. 2012; Abia et al. 2010, 2012) and of the ejecta of core-collapse supernova (CCSN) (e.g., Kjær et al. 2010; Isensee et al. 2010, 2012; Hwang & Laming 2012) may provide information about intrinsic nucleosynthesis in these objects....
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TL;DR: In this article, the authors present a survey of the X-ray emitting ejecta in the Cassiopeia A supernova remnant based on an extensive analysis of over 6000 spectral regions extracted on 2.5-10" angular scales using the Chandra 1Ms observation.
Abstract: We present a survey of the X-ray emitting ejecta in the Cassiopeia A supernova remnant based on an extensive analysis of over 6000 spectral regions extracted on 2.5-10" angular scales using the Chandra 1 Ms observation. We interpret these results in the context of hydrodynamical models for the evolution of the remnant. The distributions of fitted temperature and ionization age are highly peaked and suggest that the ejecta were subjected to multiple secondary shocks. Based on the fitted emission measure and element abundances, and an estimate of the emitting volume, we derive masses for the X-ray emitting ejecta as well as showing the distribution of the mass of various elements over the remnant. The total shocked Fe mass appears to be roughly 0.14 Solar Mass, which accounts for nearly all of the mass expected in Fe ejecta. We find two populations of Fe ejecta, that associated with normal Si-burning and that associated with alpha-rich freeze-out, with a mass ratio of approximately 2:1. Surprisingly, essentially all of this Fe (both components) is well outside the central regions of the SNR, presumably having been ejected by hydrodynamic instabilities during the explosion. We discuss this, and its implications for the neutron star kick.
190 citations
Cites background from "The Three-Dimensional Structure of ..."
...Isensee et al. (2010) demonstrate that [O IV] is more plausibly the dominant component of this blend, though they do claim a 2σ detection of [Fe II] 17.94 µm from the center when all spatial bins are summed....
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TL;DR: The authors used the Spitzer Space Telescope's Infrared Spectrograph to map nearly the entire extent of Casiopeia A between 5 and 40 μm, using infrared and Chandra X-ray Doppler velocity measurements.
Abstract: We used the Spitzer Space Telescope's Infrared Spectrograph to map nearly the entire extent of Cassiopeia A between 5 and 40 μm. Using infrared and Chandra X-ray Doppler velocity measurements, along with the locations of optical ejecta beyond the forward shock, we constructed a three-dimensional model of the remnant. The structure of Cas A can be characterized into a spherical component, a tilted thick disk, and multiple ejecta jets/pistons and optical fast-moving knots all populating the thick disk plane. The Bright Ring in Cas A identifies the intersection between the thick plane/pistons and a roughly spherical reverse shock. The ejecta pistons indicate a radial velocity gradient in the explosion. Some ejecta pistons are bipolar with oppositely directed flows about the expansion center while some ejecta pistons show no such symmetry. Some ejecta pistons appear to maintain the integrity of the nuclear burning layers while others appear to have punched through the outer layers. The ejecta pistons indicate a radial velocity gradient in the explosion. In three dimensions, the Fe jet in the southeast occupies a "hole" in the Si-group emission and does not represent "overturning," as previously thought. Although interaction with the circumstellar medium affects the detailed appearance of the remnant and may affect the visibility of the southeast Fe jet, the bulk of the symmetries and asymmetries in Cas A are intrinsic to the explosion.
164 citations
Cites background or methods from "The Three-Dimensional Structure of ..."
...The area between the faces contains relatively weaker emission from Si, S, and O ejecta as demonstrated in Figure 5 and by Isensee et al. (2010)....
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...A more detailed comparison between the low- and high-resolution spectra near the center of Cas A is presented in Isensee et al. (2010)....
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...Other scenarios for why we have not detected Fe in the unshocked ejecta are explored by Isensee et al. (2010)....
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...Support for this interpretation is provided by the high-resolution Spitzer spectra in Isensee et al. (2010)1....
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...In Isensee et al. (2010) we explore the detailed structure of the thick disk, and the relationship between the Si and O layers before they have been influenced by the reverse shock....
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References
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01 Jan 1989
TL;DR: In this paper, a comparison of theory with observations internal dynamics of gaseous nebulae interstellar dust H II regions in the galactic context is presented. But the results are limited to the case of active galactic nuclei.
Abstract: Photoionization equilibrium thermal equilibrium calculation of emitted spectrum comparison of theory with observations internal dynamics of gaseous nebulae interstellar dust H II regions in the galactic context planetary nebulae nova and supernova remnants active galactic nuclei - diagnostic and physics active galactic nuclei - results.
6,090 citations
TL;DR: In this paper, it was shown that the prompt bounce-shock mechanism is not the driver of supernova explosions, and that the delayed neutrino-heating mechanism can produce explosions without the aid of multi-dimensional processes only if the progenitor star has an ONeMg core inside a very dilute He-core, i.e., has a mass in the 8-10 M⊙ range.
762 citations
TL;DR: In this article, the stability of standing, spherical accretion shocks is examined in core-collapse supernovae, star formation, and accreting white dwarfs and neutron stars.
Abstract: We examine the stability of standing, spherical accretion shocks. Accretion shocks arise in core-collapse supernovae (the focus of this paper), star formation, and accreting white dwarfs and neutron stars. We present a simple analytic model and use time-dependent hydrodynamics simulations to show that this solution is stable to radial perturbations. In two dimensions we show that small perturbations to a spherical shock front can lead to rapid growth of turbulence behind the shock, driven by the injection of vorticity from the now nonspherical shock. We discuss the ramifications this instability may have for the supernova mechanism.
691 citations
TL;DR: In this paper, it was shown that the prompt bounce-shock mechanism is not the driver of supernova explosions, and that the delayed neutrino-heating mechanism can produce explosions without the aid of multi-dimensional processes only if the progenitor star has an ONeMg core inside a very dilute He-core.
Abstract: Advances in our understanding and the modeling of stellar core-collapse and supernova explosions over the past 15 years are reviewed, concentrating on the evolution of hydrodynamical simulations, the description of weak interactions and nuclear equation of state effects, and new insights into the nucleosynthesis occurring in the early phases of the explosion, in particular the neutrino-p process. The latter is enabled by the proton-richness of the early ejecta, which was discovered because of significant progress has been made in the treatment of neutrino transport and weak interactions. This progress has led to a new generation of sophisticated Newtonian and relativistic hydrodynamics simulations in spherical symmetry. Based on these, it is now clear that the prompt bounce-shock mechanism is not the driver of supernova explosions, and that the delayed neutrino-heating mechanism can produce explosions without the aid of multi-dimensional processes only if the progenitor star has an ONeMg core inside a very dilute He-core, i.e., has a mass in the 8--10 solar mass range. Hydrodynamic instabilities of various kinds have indeed been recognized to occur in the supernova core and to be of potential importance for the explosion. Neutrino-driven explosions, however, have been seen in two-dimensional simulations with sophisticated neutrino transport so far only when the star has a small iron core and low density in the surrounding shells as being found in stars near 10--11 solar masses. The explosion mechanism of more massive progenitors is still a puzzle. It might involve effects of three-dimensional hydrodynamics or might point to the relevance of rapid rotation and magnetohydrodynamics, or to still incompletely explored properties of neutrinos and the high-density equation of state.
582 citations
"The Three-Dimensional Structure of ..." refers background in this paper
...Although the initial conditions are well understood, the nature of the piston responsible for the explosion itself is not, with most groups proposing neutrino-driven shocks, while others utilize diffusive, magnetic buoyancy or neutrino-bubble instabilities (Janka et al. 2007)....
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406 citations
"The Three-Dimensional Structure of ..." refers background in this paper
...Previous authors observing ejecta in the optical found that the center of expansion of the ejecta was offset along the LOS from the geometrical center of the partial spherical shell (caused by ejecta interacting with the Remnant Reverse Shock) by ∼770 km s−1 (Reed et al. 1995)....
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...Emission at most wavelengths, including the infrared, is dominated by a ∼120′′ radius “Bright Ring,” which corresponds to ∼2 pc at Cas A’s estimated distance of 3.4 kpc (Reed et al. 1995)....
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...However, Reed et al. (1995) speculated that this was due to a difference in density of the circumstellar material between the back and front of the remnant....
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...In the optical, three-dimensional Doppler reconstructions of the ejecta geometry primarily used S and O emission lines (Lawrence et al. 1995; Reed et al. 1995) and showed that ejecta on the Bright Ring lie on a spherical shell but do not uniformly fill that shell; most of the ejecta lie nearly in…...
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