Suzaku X-Ray Imaging and Spectroscopy of Cassiopeia A

TL;DR

This paper presents Suzaku X-ray observations of Cassiopeia A, revealing dominant non-thermal emission, detection of highly ionized elements, and spatial correlation with TeV gamma-ray peaks, shedding light on particle acceleration in the remnant.

Contribution

First detailed Suzaku X-ray spectral and imaging analysis of Cassiopeia A highlighting non-thermal dominance and element-specific emissions, linking X-ray and gamma-ray emission regions.

Findings

Non-thermal emission dominates the 4-10 keV continuum.

Detection of K-shell lines from highly ionized elements including Cr.

Spatial correlation between non-thermal X-ray peaks and TeV gamma-ray emission.

Abstract

Suzaku X-ray observations of a young supernova remnant, Cassiopeia A, were carried out. K-shell transition lines from highly ionized ions of various elements were detected, including Chromium (Cr-Kalpha at 5.61 keV). The X-ray continuum spectra were modeled in the 3.4--40 keV band, summed over the entire remnant, and were fitted with a simplest combination of the thermal bremsstrahlung and the non-thermal cut-off power-law models. The spectral fits with this assumption indicate that the continuum emission is likely to be dominated by the non-thermal emission with a cut-off energy at > 1 keV. The thermal-to-nonthermal fraction of the continuum flux in the 4-10 keV band is best estimated as ~0.1. Non-thermal-dominated continuum images in the 4--14 keV band were made. The peak of the non-thermal X-rays appears at the western part. The peak position of the TeV gamma-rays measured with HEGRA and MAGIC is also shifted at the western part with the 1-sigma confidence. Since the location of the X-ray continuum emission was known to be presumably identified with the reverse shock region, the possible keV-TeV correlations give a hint that the accelerated multi-TeV hadrons in Cassiopeia A are dominated by heavy elements in the reverse shock region.