J/ApJ/441/307 Proper motions and brightness of Cas A (Anderson+ 1995)
The deceleration powering of synchrotron emission from ejecta components
in supernova remnant Cassiopeia A
Anderson M.C., Rudnick L.
<Astrophys. J. 441, 307 (1995)>
=1995ApJ...441..307A 1995ApJ...441..307A (SIMBAD/NED BibCode)
ADC_Keywords: Supernova remnants ; Proper motions ; Radio sources
Keywords: ISM: individual (Cassiopeia A) - ISM: kinematics and dynamics -
ISM: structure - supernova remnants - techniques: interferometric
Abstract:
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 quantify 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 lambda=6
and 20cm, spanning a total time baseline of 12yr. 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.
Objects:
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RA (2000) DE Designation(s)
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23 23 12.6 +58 48 48 Cas A = SNR 111.7-02.1
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3 106 304 Results of multi-epoch fits
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Byte-by-byte Description of file: table3
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Bytes Format Units Label Explanations
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1- 3 I3 --- Knot [1/304]+ Knot designation number
5- 7 I3 --- KnotT ? Designation number of Tuffs
(1986MNRAS.219...13T 1986MNRAS.219...13T), for knots which
are clearly in both samples
9- 14 F6.1 arcsec Xpos Epoch 1987 knot position (1)
17- 22 F6.1 arcsec Ypos Epoch 1987 knot position (1)
25- 30 F6.1 arcsec BoxX1 Box defining the regression region used for
each knot (1)
33- 38 F6.1 arcsec BoxY1 Box defining the regression region used for
each knot (1)
41- 46 F6.1 arcsec BoxX2 Box defining the regression region used for
each knot (1)
49- 54 F6.1 arcsec BoxY2 Box defining the regression region used for
each knot (1)
56- 61 F6.3 arcsec/yr pmRA Proper motion in right ascension
64- 68 F5.3 arcsec/yr e_pmRA rms uncertainty in pmRA (68% confidence)
71- 76 F6.3 arcsec/yr pmDE Proper motion in declination
79- 83 F5.3 arcsec/yr e_pmDE rms uncertainty in pmDE (68% confidence)
86- 89 F4.1 mJy B Estimate of knot brightness at lambda=6cm
(mJy/beam, epoch 1987)
91- 96 F6.3 yr-1 DB/B Annual fractional brightness change relative
to the large-scale ring
99-103 F5.3 yr-1 e_DB/B rms uncertainty in DB/B (68% confidence)
106 I1 --- Nobs Number of epochs of data used in multi-epoch
determinations
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Note (1): Positions measured with respect to the optical expansion center at
alpha(1950)= 23h21m11s90, delta(1950) = +58deg32'17.6"
(Van den Bergh & Kamper 1983ApJ...268..129V 1983ApJ...268..129V)
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History: Prepared via OCR at CDS.
(End) James Marcout, Patricia Bauer [CDS] 02-Oct-1996