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We have studied the X-ray emission from four historical Type-II supernovae(the newly-discovered 1941C in NGC 4631 and 1959D in NGC 7331; and 1968D, 1980Kin NGC 6946), using Chandra ACIS-S imaging. In particular, the first three arethe oldest ever found in the X-ray band, and provide constraints on theproperties of the stellar wind and circumstellar matter encountered by theexpanding shock at more advanced stages in the transition towards the remnantphase. We estimate emitted luminosities ~ 5 x 10^{37} erg/s for SN 1941C, ~ afew x 10^{37} erg/s for SN 1959D, ~ 2 x 10^{38} erg/s for SN 1968D, and ~ 4 x10^{37} erg/s for SN 1980K, in the 0.3-8 keV band. X-ray spectral fits to SN1968D suggest the presence of a harder component, possibly a power law withphoton index ~ 2, contributing ~ 10^{37} erg/s in the 2-10 keV band. Wespeculate that it may be evidence of non-thermal emission from a Crab-likeyoung pulsar.

The oldest X-ray supernovae: X-ray emission from 1941C, 1959D, 1968D