Reverse Shock Revisited in Cassiopeia A with Chandra

TL;DR

This study uses Chandra X-ray data to analyze the reverse shock in Cassiopeia A, revealing its location, velocity, and asymmetry, which enhances understanding of supernova remnant dynamics.

Contribution

It provides detailed measurements of the reverse shock's position and velocity in Cassiopeia A, confirming and cross-validating previous methods, and highlights asymmetry linked to explosion dynamics.

Findings

Reverse shock location determined at ~1.7 and 1.35 arcmin in NW and SE.

Reverse shock velocities are ~3950 km/s (NW) and ~2900 km/s (SE).

Asymmetry suggests asymmetric explosion influences remnant features.

Abstract

Using data from the Chandra X-Ray Observatory, we revisited the reverse shock in the supernova remnant (SNR) Cassiopeia A.Based on the spectroscopic of a series of annuli in the northwest (NW) and southeast (SE), we get the radial profiles of the S/Si K-alpha line flux ratio and Fe K-alpha line centroid energy. They both show monotonic increase, confirming that the Si- and Fe-rich ejecta are heated by the reverse shock.The abrupt change of the S and Si line flux ratio is clearly observed in Cassiopeia A, leading to the determination of the reverse shock location (~1.71+-0.16 arcmin and ~1.35+-0.18 arcmin in the NW and SE, with respect to the central source). By comparing the radial profiles of S and Si line flux, we find that the reverse shock is moving outward in the frame of the observer, and the velocities are ~3950+-210 km/s and ~2900+-260 km/s in the NW and SE, respectively. In contrast, the velocities become ~1150 km/s (NW) and ~1300 km/s (SE) in the ejecta frame. Our measured reverse shock velocities are quite consistent with those obtained from the X-ray and/or optical images. It therefore supplies a crosscheck of the accuracy for the two available methods to measure the reverse shock velocity in SNRs. Both the location and the velocity of the reverse shock show apparent asymmetry, suggesting that the asymmetric explosion of the progenitor plays a key role in the interaction between the reverse shock and the ejecta, ultimately shaping complex features observed in SNRs.