Evidence for past interaction with an asymmetric circumstellar shell in the young SNR Cassiopeia A

Abstract

Context. Observations of the supernova remnant (SNR) Cassiopeia A (Cas A) show significant asymmetries in the reverse shock that cannot be explained by models describing a remnant expanding through a spherically symmetric wind of the progenitor star. Aims. We investigate whether a past interaction of Cas A with a massive asymmetric shell of the circumstellar medium can account for the observed asymmetries of the reverse shock. Methods. We performed three-dimensional (3D) (magneto)-hydrodynamic simulations that describe the remnant evolution from the SN explosion to its interaction with a massive circumstellar shell. The initial conditions (soon after the shock breakout at the stellar surface) are provided by a 3D neutrino-driven SN model whose morphology closely resembles Cas A (Wongwathanarat et al. 2017). The SNR simulations cover ≈ 2000 years of evolution and include all physical processes necessary to describe the remnant-shell interaction. We explored the parameter space of the shell, searching for a set of parameters able to produce reverse shock asymmetries at the age of ≈ 350 years analogous to those observed in Cas A.Results. The interaction of the remnant with the shell can match the observed asymmetries in the reverse shock if the shell was asymmetric with the densest portion in the (blueshifted) nearside to the northwest (NW). According to our favorite model, the shell was thin (thickness σ ≈ 0.02 pc) with a radius r sh ≈ 1.5 pc from the center of the explosion. The reverse shock shows the following asymmetries at the age of Cas A: i) it moves inward in the observer frame in the NW region, while it moves outward in other regions; ii) the geometric center of the reverse shock is offset to the NW by ≈ 0.1 pc from the geometric center of the forward shock; iii) the reverse shock in the NW region has enhanced nonthermal emission because, there, the ejecta enter the reverse shock with a higher relative velocity (between 4000 and 7000 km s −1 ) than in other regions (below 2000 km s −1 ). Conclusions. The main asymmetries observed in the reverse shock of Cas A can be interpreted as signatures of the interaction of the remnant with an asymmetric dense circumstellar shell that occurred between ≈ 180 and ≈ 240 years after the SN event. We suggest that the shell was, most likely, the result of a massive eruption from the progenitor star that occurred about 10 5 years prior to core-collapse. We estimate a total mass of the shell of M sh ≈ 2.6 M ⊙ .

The Role of Jets in Exploding Supernovae and in Shaping their Remnants

“…The dispute exists also in the analysis of SNR Cassiopeia A, for which Wongwathanarat et al (2015); Orlando et al (2021) and Orlando et al (2022) argued that the neutrino-driven explosion mechanism can account for the distribution of some metals, while in Soker (2017b) I argued that jets seem to have played a crucial role is the shaping of Cassiopeia A during its explosion. Orlando et al (2016) already argued that instabilities alone cannot account for all morphological features of Cassiopeia A.…”

Rectangular core-collapse supernova remnants: application to Puppis A

“…Furthermore, the dense environment hosts star formation processes and typically is highly magnetized (Hennebelle & Falgarone 2012), influencing the development of circumstellar structures (Pardi et al 2017) and supernova remnants (Korpi et al 1999a,b), which in turn generate and maintain the level of turbulence of the ISM (Seifried et al 2018). A more realistic depiction of the supernova-wind interaction in a magnetized ISM would require full 3D magneto-hydrodynamical simulations, better modelling of the circumstellar medium around the massive progenitor star (Meyer et al 2021b), as well as the propagation of the supernova blastwave in it (Orlando et al 2021(Orlando et al , 2022.…”

“…Recently, Das et al (2022a) noted a softening of the non-thermal particle spectra when the shock wave goes through shocked circumstellar material. Similarly, the role of material expelled throughout pulsating mass-loss events occurring during the last century of the progenitor's life has been highlighted in the context of the asymmetries in the expanding shock wave of Cassiopea A (Orlando et al 2021(Orlando et al , 2022. More generally, the lengthening effects of an organised magnetic field on the morphology of stellar wind bubble was analysed by van Marle et al (2015).…”

The sculpting of rectangular and jet-like morphologies in supernova remnants by anisotropic equatorially confined progenitor stellar winds

“…This evolution takes place in an ISM with a uniform magnetic field, producing an asymmetric circumstellar medium in which the SN ejecta expands, and results in a projected rectangular morphology. Other studies on (a)symmetric core-collapse SNRs include Meyer et al (2015Meyer et al ( , 2020Meyer et al ( , 2021a, Orlando et al (2021Orlando et al ( , 2022, Soker (2021), andKaplan (2021).…”