Instabilities and Clumping in Type Ia Supernova Remnants
TL;DR: In this paper, high-resolution hydrodynamical simulations in spherical polar coordinates of a Type Ia supernova interacting with a constant density interstellar medium are presented, based on observations of X-ray knots and the protrusion in the southeast outlin of Tycho's supernova remnant, including clumping in the ejecta.
Abstract: We present two-dimensional high-resolution hydrodynamical simulations in spherical polar coordinates of a Type Ia supernova interacting with a constant density interstellar medium. The ejecta are assumed to be freely expanding with an exponential density profile. The interaction gives rise to a double-shocked structure susceptible to hydrodynamic instabilities. The Rayleigh-Taylor instability initially grows, but the Kelvin-Helmholtz instability takes over, producing vortex rings. The nonlinear instability initially evolves toward longer wavelengths and eventually fades away when the reverse shock front is in the flatter part of the supernova density distribution. Based on observations of X-ray knots and the protrusion in the southeast outlin of Tycho's supernova remnant, we include clumping in the ejecta. The clump interaction with the reverse shock induces Rayleigh-Taylor and Kelvin-Helmholtz instabilities on the clump surface that facilitate fragmentation. In order to survive crushing and to have a bulging effect on the forward shock, the clump's initial density ratio to the surrounding ejecta must be at least 100 for the conditions in Tycho's remnant. The 56Ni bubble effect may be important for the development of clumpiness in the ejecta. The observed presence of an Fe clump would then require a non-radioactive origin for this Fe, possibly 54Fe. The large radial distance of the X-ray emitting Si and S ejecta from the remnant center indicates that they were initially in clumps.
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TL;DR: In this paper , velocity measurements of 59 clumpy, metal-rich ejecta knots in the supernova remnant (SNR) of SN 1572 (Tycho) are presented.
Abstract: We present our velocity measurements of 59 clumpy, metal-rich ejecta knots in the supernova remnant (SNR) of SN 1572 (Tycho). We use our 450 ks Chandra High Energy Transmission Grating Spectrometer observation to measure the Doppler shift of the He-like Si Kα line-center wavelength emitted from these knots to find their line-of-sight (radial) velocities (v r ). We find v r up to ∼5500 km s−1, with roughly consistent speeds between blueshifted and redshifted ejecta knots. We also measure the proper motions (PMs) for our sample based on archival Chandra Advanced CCD Imaging Spectrometer data taken from 2003, 2009, and 2015. We estimate PMs up to 0.″35 yr−1, which corresponds to a transverse velocity of about 5800 km s−1 for the distance of 3.5 kpc to Tycho. Our v r and transverse velocity measurements imply space velocities of ∼1900–6000 km s−1 for the ejecta knots in Tycho. We estimate a new expansion center of R.A.(J2000) = 00h25m18s.725 ± 1.ˢ157 and decl.(J2000) = +64°08′02.″5 ± 11.″2 from our PM measurements, consistent to within ∼13″ of the geometric center. The distribution of space velocities throughout the remnant suggests that the southeast quadrant generally expands faster than the rest of the SNR. We find that blueshifted knots are projected more in the northern shell, while redshifted knots are more in the southern shell. The previously estimated reverse shock position is consistent with most of our estimated ejecta distribution; however, some ejecta show deviations from the 1D picture of the reverse shock.
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TL;DR: In this article , the stability of two-superimposed incompressible magnetized plasma fluids incorporating finite ion Larmor radius (FLR) correction and suspended dust particulates is studied.
Abstract: Abstract In this theoretical exploration, the stabilizing or destabilizing impacts of the rotation, electron inertia, and electrical resistivity on the Kelvin–Helmholtz stability in two-superimposed incompressible magnetized plasma fluids incorporating finite ion Larmor radius (FLR) correction and suspended dust particulates are studied. The linearized perturbation equations for the Kelvin–Helmholtz instability problems are determined based on the magnetohydrodynamic (MHD) model. The general dispersion equation is derived by using appropriate boundary conditions. By the numerical estimation, the finite ion Larmor radius does not have any significant role in the Kelvin–Helmholtz instability of the magnetoplasma medium. The graphical estimates reveal the destabilization impact of the resistivity and electron inertia on the Kelvin–Helmholtz hydrodynamic plasma fluid system. In this paper, graphical representations have also analyzed the effect of rotation on the Kelvin–Helmholtz stability growth rate with the variation of electron inertia and resistivity. This current analysis provides pertinent information about the significant involvement of this considered system in space and astrophysical structures.
TL;DR: In this article , the linear MHD Kelvin-Helmholtz instability (KHI) in an anisotropic plasma is studied and dispersion equations for the KHI of quasi-transverse modes are derived considering the finite width of the transition zone with different velocity profiles.
Abstract:
The linear MHD Kelvin-Helmholtz instability (KHI) in an anisotropic plasma is studied. The governing equations obtained as the 16 moments of Boltzmann-Vlasov kinetic equations, including the heat flow, are applied. In the case of tangential discontinuity between the supersonic flows along the magnetic field calculated growth rates as functions of the anisotropic plasma properties allow us to conclude that quasi-transverse modes grow faster. Then dispersion equations for the KHI of quasi-transverse modes are derived considering the finite width of the transition zone with different velocity profiles. For these modes, when the role of heat flow is not important, the plasma parameters are controlled so that the fundamental plasma instabilities (firehose and mirror) do not affect the KHI. The problem is solved analytically, which will be helpful in verifying for numerical simulation. In contrast to the tangential discontinuity, the finite width of the transition layer confines KHI excitation as the wavenumber increases. In the general case of oblique propagation (when a heat flux complicates the problem), the boundary value problem is solved to determine the spectral eigenvalues. In particular, it is observed that fundamental plasma instabilities that arise in the transition zone between flows with a finite width can modify and considerably enhance KHI.
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TL;DR: The role of radioactivities in astronomy with radioactivity is discussed in this article, with a focus on the role of Radioactive Isotopes in low-and intermediate-mass stars.
Abstract: Part I The Role of Radioactivities in Astrophysics.- Introduction to Astronomy With Radioactivity.- The Role of Radioactive Isotopes in Astrophysics.- Part II Specific Sources of Cosmic Isotopes.- Radioactivities in Low-and Intermediate-Mass Stars.- Massive Stars and their Supernovae.- Binary Systems and Their Nuclear Explosions.- Part III Special Places to Observe Cosmic Isotopes.- Distributed Radioactivities.- Part IV Tools for the Study of Radioactivities in Astrophysics.- Nuclear Reactions.- Instruments for Observations of Radioactivities.- Part V Epilogue.- Perspectives.- Annotations on Chemical Evolution.- Radionuclides and Their Stellar Origins.- Milestones in the Science of Cosmic Radioactivities.- Glossary: Key Terms in Astronomy With Radioactivities.- Index.
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