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Table 2

Number of SNRsa with the various classifications and of the various types.

SNR type Axisymmetricb Not axisymmetric Total
Very clearly defined Somewhat defined Not clearly defined

Shell 27 17 43 112 199
Plerionic-composite 1 0 9 31 41
Thermal-composite 4 3 2 27 36
Thermal & plerionic-composite 1 0 1 5 7
Unknown 0 1 3 6 10
Total 33 21 58 181 293



This table represents the up-to-date numbers at the time of this writing, but the companion website is dynamic and classifications and exact counts of SNRs of various types are subject to change.


The axisymmetric SNRs include both the so-called bilateral SNRs with two distinct limbs of emission and also the one-sided shells. The morphology of the other SNRs are not consistent with this definition, thus we refer to these as not-axisymmetric. This includes SNRs with a round appearance, of which there are 43 candidates (33 shell, 7 plerionic composite, and 3 thermal composite). We consider only 15 of these candidates to be very clearly defined or somewhat defined, with the remainder (28 candidates) being not clearly defined.

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