Abstract
Aims. The Vishniac instability is thought to explain the complex structure of radiative supernova remnants (SNRs) when a blast wave has propagated from a central explosion. Methods. In this paper, we present numerical studies with the two-dimensional (2D) code HADES. We compare simulations of non-cooling perturbed SNRs, with simulations of perturbed SNRs experiencing radiative losses. In the first case, a low adiabatic index involves a high compression rate that can mimic the effect of radiative losses, whereas a cooling function is used in the second case. Results. The development of the perturbation is analyzed with and without cooling. First, we show that with no cooling but with a low adiabatic index, the perturbation grows in agreement with the theory. Second, although in a first stage the initial Vishniac instability (VI) vanishes for SNR undergoing radiative losses and a large adiabatic index equal to 5/3, simulations show that at a later time a new and growing perturbation appears and the mode l′ of this new perturbation is twice the mode l of the initial one (l′ = 2 × l). Conclusions. Simulating SNR evolutions in similar conditions to theoretical conditions, that is, an adiabatic expansion and adiabatic index lower than 1.2, VI is found to occur in accordance with theoretical predictions. When cooling, instead of a low adiabatic index, which is included in the model, simulations demonstrate that in the late stage of SNR evolution, a doubled mode VI develops even for an adiabatic index equal to 5/3. These two phenomena, VI for high adiabatic index and the mode doubling process, are new and demonstrated in this paper.
Highlights
The study of the structure of supernova remnants (SNRs) is a difficult task because SNRs experience various physical processes during their evolution
From the beginning of its spherical propagation, the blast wave (BW) created by the supernova (SN) pushes away the surrounding material, that is, the circumstellar medium and/or interstellar medium (ISM), and a dense shell forms just behind the BW front while a nearly empty but very hot bubble is created in the inner, central region, of the SNR
We have shown that the evolution of a spatial perturbation in a SNR is very different according to whether the SNR experiences cooling or not
Summary
The study of the structure of supernova remnants (SNRs) is a difficult task because SNRs experience various physical processes during their evolution. This paper is the continuation of several steps achieved in our hierarchical study of the development of the VI and presents new numerical investigations They take into account a different approach concerning the BW expansion in the radiative regime; radiative cooling is included in our model by energy losses, the adiabatic index γ does not need to approach one in order to mimic radiative losses, contrary to the Vishniac (1983) theory. The authors do not include any cooling in their studies (Vishniac 1983; Ryu & Vishniac 1987) They used an adiabatic index γ going to one in order to get a strong compression in the shocked material. These results are completely new and reveal an unknown behavior of the VI the various situations (VI only, cooling only, and VI with cooling) are compared in Sect. 7 and our conclusion is given
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