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

Recent discovery of the year-scale variability in the synchrotron X-ray emission of the supernova remnant (SNR) RX J713.7-3946 has initiated our study of multiepoch 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 y...

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Bibliographic Details
Published in:The Astrophysical journal 2008-04, Vol.677 (2), p.L105-L108
Main Authors: Uchiyama, Yasunobu, Aharonian, Felix A
Format: Article
Language:English
Subjects:
Astronomy
Earth, ocean, space
Exact sciences and technology
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Summary:Recent discovery of the year-scale variability in the synchrotron X-ray emission of the supernova remnant (SNR) RX J713.7-3946 has initiated our study of multiepoch 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.
ISSN:1538-4357
0004-637X
1538-4357
DOI:10.1086/588190