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

TL;DR

This study analyzes X-ray emissions from four of the oldest known supernovae, providing insights into their circumstellar environments and potential non-thermal emission sources like young pulsars.

Contribution

It presents the first X-ray observations of supernovae from 1941C, 1959D, and 1968D, offering new constraints on their late-stage evolution and circumstellar interactions.

Findings

X-ray luminosities range from 5 x 10^{37} to 2 x 10^{38} erg/s.

Spectral analysis of SN 1968D indicates a possible non-thermal component.

First X-ray detections of these ancient supernovae provide new insights into supernova evolution.

Abstract

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, 1980K in NGC 6946), using Chandra ACIS-S imaging. In particular, the first three are the oldest ever found in the X-ray band, and provide constraints on the properties of the stellar wind and circumstellar matter encountered by the expanding shock at more advanced stages in the transition towards the remnant phase. We estimate emitted luminosities ~ 5 x 10^{37} erg/s for SN 1941C, ~ a few x 10^{37} erg/s for SN 1959D, ~ 2 x 10^{38} erg/s for SN 1968D, and ~ 4 x 10^{37} erg/s for SN 1980K, in the 0.3-8 keV band. X-ray spectral fits to SN 1968D suggest the presence of a harder component, possibly a power law with photon index ~ 2, contributing ~ 10^{37} erg/s in the 2-10 keV band. We speculate that it may be evidence of non-thermal emission from a Crab-like young pulsar.