J/ApJ/441/307ivo://CDS.VizieR/J/ApJ/441/307doi:10.26093/cds/vizier.14410307CDSAnderson M.C.Rudnick L.1999-12-23T09:43:00Z1999-12-23T10:42:56ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frsupernova-remnantsproper-motionsradio-sourcesThe 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.1995ApJ...441..307Ahttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/441/307CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/441/307https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/441/307http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/441/307https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/441/307https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/441/307http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/441/307GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapRadiodefaultJ/ApJ/441/307/table3Results of multi-epoch fitsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintKnot[1/304]+ Knot designation numbermeta.id;meta.mainintprimaryindexedKnotT? Designation number of Tuffs (1986MNRAS.219...13T), for knots which are clearly in both samplesmeta.idintnullableXposEpoch 1987 knot position (1)arcsecpos.projfloatYposEpoch 1987 knot position (1)arcsecpos.projfloatBoxX1Box defining the regression region used for each knot (1)arcsecinstr.paramfloatBoxY1Box defining the regression region used for each knot (1)arcsecinstr.paramfloatBoxX2Box defining the regression region used for each knot (1)arcsecinstr.paramfloatBoxY2Box defining the regression region used for each knot (1)arcsecinstr.paramfloatpmRAProper motion in right ascensionarcsec/yrpos.pm;pos.eq.rafloate_pmRArms uncertainty in pmRA (68% confidence)arcsec/yrstat.errorfloatpmDEProper motion in declinationarcsec/yrpos.pm;pos.eq.decfloate_pmDErms uncertainty in pmDE (68% confidence)arcsec/yrstat.errorfloatBEstimate of knot brightness at lambda=6cm (mJy/beam, epoch 1987)mJyphot.flux.density;em.radio.3-6GHzfloatDB/BAnnual fractional brightness change relative to the large-scale ringyr**-1src.varfloate_DB/Brms uncertainty in DB/B (68% confidence)yr**-1stat.errorfloatNobsNumber of epochs of data used in multi-epoch determinationsmeta.numberint