Characterizing the non-thermal emission of Cas A

TL;DR

This study analyzes a 1 Ms Chandra observation of Cas A to localize and characterize its non-thermal X-ray emission, revealing that most emission originates from the inner ring associated with the reverse shock, with implications for particle acceleration.

Contribution

It employs a Lucy-Richardson deconvolution technique and spectral analysis to determine the origin of X-ray synchrotron emission in Cas A, providing new insights into shock dynamics and emission regions.

Findings

Most continuum emission comes from the inner ring at the reverse shock.

Filaments in the inner ring are dominated by X-ray synchrotron emission.

Hard X-ray emission regions contribute about 54% of total emission, lower than previous estimates.

Abstract

We report on our analysis of the 1 Ms Chandra observation of the supernova remnant Cas A in order to localize, characterize and quantify its non-thermal X-ray emission. More specifically, we investigated whether the X-ray synchrotron emission from the inside of the remnant is from the outward shock, but projected toward the inner ring, or from the inner shell. We tackle this problem by employing a Lucy-Richardson deconvolution technique and measuring spectral indices in the 4.2-6 keV band. We show that most of the continuum emission is coming from an inner ring that coincides with the location of the reverse shock. This inner ring includes filaments, whose X-ray emission has been found to be dominated by X-ray synchrotron emission. The X-ray emission from these filaments, both at the forward shock and from the inner ring, have relatively hard spectra with spectral index > -3.1. The regions emitting hard X-ray continuum contribute about 54% of the total X-ray emission in the 4.2-6 keV. This is lower than suggested by extrapolating the hard X-ray spectrum as measured by BeppoSAX-PDS and INTEGRAL. This can be reconciled by assuming a gradual steepening of the spectrum toward higher energies. We argue that the X-ray synchrotron emission is mainly coming from the Western part of the reverse shock. The reverse shock in the West is almost at rest in our observation frame, corresponding to a relatively high reverse shock velocity of ~6000 km/s in the frame of the freely expanding ejecta.