Asymmetric Expansion of the Fe ejecta in Kepler's Supernova Remnant

TL;DR

This study reveals asymmetric expansion of Fe ejecta in Kepler's SNR, showing red-shifted central material and high-velocity blue-shifted clumps, providing insights into supernova explosion mechanisms.

Contribution

First spectral and imaging analysis demonstrating asymmetric Fe ejecta expansion in Kepler's SNR using Chandra data, suggesting multiple origins for the asymmetry.

Findings

Fe ejecta shows red-shifted central region and blue-shifted outer clumps.

Estimated velocities: ~2000 km/s for red-shifted and ~3000 km/s for blue-shifted structures.

Possible interaction of Fe ejecta with dense circumstellar medium.

Abstract

The ejecta kinematics of supernova remnants (SNRs) is one of crucial clues to understand the explosion mechanism of type Ia supernovae (SNe). In particular, the kinematic asymmetry of iron-peak elements provides the key to understanding physical processes taking place in the core of the exploding white dwarfs (WDs) although it has been poorly understood by observations. In this paper, we show for the first time the asymmetric expansion structure in the line-of-sight direction of Fe ejecta in Kepler's SNR revealed by spectral and imaging analysis using the Chandra archival data. We found that the K$\alpha$ line centroid energy and line width is relatively lower ($<$ 6.4 keV) and narrower ($\sim$80 eV) around the center of the remnant, which implies that the majority of the Fe ejecta in the central region is red-shifted. At the outer regions, we identify bright blue-shifted structures as it might have been ejected as high velocity dense clumps. Taking into account the broad population of the Fe charge states, we estimate the red-shifted velocity of ~2,000 km/s and the blue-shifted velocity of ~3,000 km/s for each velocity structure. We also present a possibility that a portion of the Fe ejecta near the center are interacting with the dense circumstellar medium (CSM) on the near side of the remnant. As the origin of the asymmetric motion of the Fe ejecta, we suggest three scenarios, (1) the asymmetric distribution of the CSM, (2) the "shadow" in Fe cast by the companion star, and (3) the asymmetric explosion.