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Description
We present a survey of optically emitting supernova remnants (SNRs) in M31 based on H{alpha} and [S II] images in the Local Group Survey. Using these images, we select objects that have [S II]:H{alpha}>0.4 and circular shapes. We identify 156 SNR candidates, of which 76 are newly found objects. We classify these SNR candidates according to two criteria: the SNR progenitor type (Type Ia and core-collapse (CC) SNRs) and the morphological type. Type Ia and CC SNR candidates make up 23% and 77%, respectively, of the total sample. Most of the CC SNR candidates are concentrated in the spiral arms, while the Type Ia SNR candidates are rather distributed over the entire galaxy, including the inner region. The CC SNR candidates are brighter in H{alpha} and [S II] than the Type Ia SNR candidates. We derive a cumulative size distribution of the SNR candidates, finding that the distribution of the candidates with 17<D<50 pc is fitted well by a power law with the power-law index {alpha}=2.53+/-0.04. This indicates that most of the SNR candidates identified in this study appear to be in the Sedov-Taylor phase. The [S II]:H{alpha} distribution of the SNR candidates is bimodal, with peaks at [S II]:H{alpha}~0.4 and~0.9. The properties of these SNR candidates vary little with the galactocentric distance. The H{alpha} and [S II] surface brightnesses show a good correlation with the X-ray luminosity of the SNR candidates that are center-bright.
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