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J/ApJ/456/234       Cas A radio knots spectral indices (Anderson+ 1996)

Sites of relativistic particle acceleration in supernova remnant Cassiopeia A Anderson M.C., Rudnick L. <Astrophys. J. 456, 234 (1996)> =1996ApJ...456..234A (SIMBAD/NED BibCode)
ADC_Keywords: Supernova remnants Keywords: acceleration of particles - cosmic rays - ISM: individual (Cassiopeia A) - radiation mechanisms: nonthermal - radio continuum: ISM - supernova remnants Abstract: We have determined the synchrotron spectral indices of 304 compact radio knots in the supernova remnant Cassiopeia A. A comparison of these data with the dynamical and brightness properties of these knots tabulated by Anderson & Rudnick (Cat. J/ApJ/441/307) indicates that spectral index shows a significant correlation with projected radius from the center of the remnant. Spectrally flat knots reside in a shell coincident with the bright radio ring, while steeper knots occupy a shell coincident with the diffuse radio plateau surrounding the ring. To a lesser extent, we find spectral index to be correlated also with the radio brightness of the knot, in the sense that brighter knots tend to have steeper spectra. No significant correlation is found between spectral index and knot deceleration or rate of brightness change. As the synchrotron spectral index traces the distribution of energy among relativistic particle populations, we use these results to study the nature of particle acceleration mechanisms active in Cas A. Given the dual shell nature of the spectral index distribution in Cas A and the lack of strong correlation between spectral index and dynamical properties of the knots, we conclude that radio-bright compact features are not sites of currently active particle acceleration in Cas A. This conclusion is in agreement with models of supersonic gaseous bullets constructed by Jones, Kang, & Tregillis (1994ApJ...432..194J). In these models, the marked synchrotron brightening which accompanies bullet deceleration is due primarily to preexisting relativistic particles radiating in rapidly amplifying shear-layer magnetic fields, rather than a large infusion of new relativistic particles accelerated in situ. Spectral variations between compact features in Cas A are more likely to reflect modulations in the background particle energy spectra within the remnant, perhaps instilled by temperature variations in the underlying thermal material. This interpretation requires that the diffuse synchrotron emission show the same spectral variations as seen in compact features; preliminary indications suggest that this is the case. Objects: ----------------------------------------- RA (2000) DE Designation(s) ----------------------------------------- 23 23 12.6 +58 48 48 Cas A = SN 1680 ----------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1 77 304 Radio knot spectral indices (epoch 1987)
See also: J/ApJ/441/307 : Proper motions and brightness of Cas A (Anderson+ 1995) Byte-by-byte Description of file: table1
Bytes Format Units Label Explanations
1- 3 I3 --- Knot Knot number 7- 9 I3 --- KnotT ? Designation number of Tuffs (1986MNRAS.219...13T) 12- 17 F6.1 arcsec Xpos Epoch 1987 knot position (1) 21- 26 F6.1 arcsec Ypos Epoch 1987 knot position (1) 30- 35 F6.1 arcsec BoxX1 Box defining the regression region used for each knot (1) 39- 44 F6.1 arcsec BoxY1 Box defining the regression region used for each knot (1) 48- 53 F6.1 arcsec BoxX2 Box defining the regression region used for each knot (1) 57- 62 F6.1 arcsec BoxY2 Box defining the regression region used for each knot (1) 66- 69 F4.2 --- alpha Spectral index 73- 76 F4.2 --- e_alpha rms uncertainty on alpha
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)
History: Prepared via OCR at CDS.
(End) James Marcout, Patricia Bauer [CDS] 25-Oct-1996
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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