TY - JOUR
T1 - The deceleration powering of synchrotron emission from ejecta components in supernova remnant Cassiopeia A
AU - Anderson, M. C.
AU - Rudnick, L.
N1 - Copyright:
Copyright 2018 Elsevier B.V., All rights reserved.
PY - 1995/3/1
Y1 - 1995/3/1
N2 - The results of a multiple-epoch radio study of secular changes in the SNR Cassiopeia A are reported and used to construct a model for the dynamical evolution of diffuse and clumpy ejecta components in the remnant. To aquantify the current dynamical status of various ejecta components, the proper motions and brightness evolution of a sample of 304 compact radio features have been accurately determined from high-quality interferometric observations of the remnant at λ = 6 and 20 cm, spanning a total time baseline of 12 yr. A simple model of homologous expansion does not provide a good fit to the measured proper motions of the radio knots. We find that a single estimate of the ejecta expansion age is not appropriate, as the expansion derived from compact features varies azimuthally and radially in the remnant and differs for subsets of knots segregated by brightness. We verify that the bulk of the radio-emitting plasma in Cas A has indeed been significantly decelerated by the current epoch; bulk expansion ages of 2.5-4 times the actual age of the remnant are measured. Based on these dynamical data, and information on the kinematics of the fast moving optical knots, we synthesize a model that directly relates the dynamics of ejecta components in Cas A to various radiative processes. This model is based on the premise that the emission from Cas A, at a variety of wavelengths, is deceleration-powered. If ejecta components are distributed over a range of internal densities, a sequential "turning-on" of components, in order of increasing density, should be observed. A model for the current emission distribution in Cas A, at radio, X-ray, and optical wavelengths, is outlined in terms of deceleration considerations.
AB - The results of a multiple-epoch radio study of secular changes in the SNR Cassiopeia A are reported and used to construct a model for the dynamical evolution of diffuse and clumpy ejecta components in the remnant. To aquantify the current dynamical status of various ejecta components, the proper motions and brightness evolution of a sample of 304 compact radio features have been accurately determined from high-quality interferometric observations of the remnant at λ = 6 and 20 cm, spanning a total time baseline of 12 yr. A simple model of homologous expansion does not provide a good fit to the measured proper motions of the radio knots. We find that a single estimate of the ejecta expansion age is not appropriate, as the expansion derived from compact features varies azimuthally and radially in the remnant and differs for subsets of knots segregated by brightness. We verify that the bulk of the radio-emitting plasma in Cas A has indeed been significantly decelerated by the current epoch; bulk expansion ages of 2.5-4 times the actual age of the remnant are measured. Based on these dynamical data, and information on the kinematics of the fast moving optical knots, we synthesize a model that directly relates the dynamics of ejecta components in Cas A to various radiative processes. This model is based on the premise that the emission from Cas A, at a variety of wavelengths, is deceleration-powered. If ejecta components are distributed over a range of internal densities, a sequential "turning-on" of components, in order of increasing density, should be observed. A model for the current emission distribution in Cas A, at radio, X-ray, and optical wavelengths, is outlined in terms of deceleration considerations.
KW - ISM: individual (Cassiopeia A)
KW - ISM: kinematics and dynamics
KW - ISM: structure
KW - Supernova remnants
KW - Techniques: interferometric
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U2 - 10.1086/175357
DO - 10.1086/175357
M3 - Article
AN - SCOPUS:11944253710
SN - 0004-637X
VL - 441
SP - 307
EP - 333
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1
ER -