Fast Variability of Nonthermal X-Ray Emission in Cassiopeia A: Probing Electron Acceleration in Reverse-Shocked Ejecta

TL;DR

This study analyzes multi-epoch Chandra X-ray data of Cassiopeia A, revealing year-scale variability in nonthermal X-ray emission linked to reverse-shocked regions, shedding light on electron acceleration processes.

Contribution

It presents the first evidence of year-scale X-ray variability in Cassiopeia A's reverse-shocked ejecta, linking it to electron acceleration and synchrotron cooling.

Findings

Year-scale variability observed in X-ray filaments.

Spectral analysis supports synchrotron origin of emission.

Variability timescale consistent with magnetic field of 1 mG.

Abstract

Recent discovery of the year-scale variability in the synchrotron X-ray emission of the supernova remnant (SNR) RX J1713.7-3946 has initiated our study of multi-epoch X-ray images and spectra of the young SNR Cassiopeia A based on the Chandra archive data taken in 2000, 2002, and 2004. We have found year-scale time variations in the X-ray intensity for a number of X-ray filaments or knots associated with the reverse-shocked regions. The X-ray spectra of the variable filaments are characterized by a featureless continuum, and described by a power law with a photon index within 1.9-2.3. The upper limits on the iron K-line equivalent width are 110 eV, which favors a synchrotron origin of the X-ray emission. The characteristic variability timescale of 4 yr can be explained by the effects of fast synchrotron cooling and diffusive shock acceleration with a plausible magnetic field of 1 mG. The X-ray variability provides a new effective way of studying particle acceleration at supernova shocks.