Fast Variability of Nonthermal X-Ray Emission in Cassiopeia A: Probing Electron Acceleration in Reverse-Shocked Ejecta
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.
Cite
@article{arxiv.0803.3410,
title = {Fast Variability of Nonthermal X-Ray Emission in Cassiopeia A: Probing Electron Acceleration in Reverse-Shocked Ejecta},
author = {Yasunobu Uchiyama and Felix Aharonian},
journal= {arXiv preprint arXiv:0803.3410},
year = {2009}
}
Comments
4 pages, 4 figures, accepted for publication in ApJ Letter