Quantitative Age Estimation of Supernova Remnants and Associated Pulsars

The age of a supernova remnant (SNR) is, though undoubtedly one of the most important properties for study of its evolution, difficult to estimate reliably in most cases. In this study, we compare the dynamical and plasma ages of the SNRs and characteristic ages of their associated pulsars with the corresponding SNRs' ages that are generally thought to be reliable ($t_{\rm r}$): historical and light-echo ages of the SNRs, kinematic ages of the ejecta knots and kinematic ages of the associated neutron stars (NS). The kinematic age of ejecta knots or a NS is the time that they have taken to reach the current positions from the explosion center. We use all of the available 24 systems for which $t_{\rm r}$ is already available (historical, light-echo, and ejecta kinematic ages) or measurable (NS kinematic age). We estimate the NS kinematic ages for eight SNR-NS systems by determining quantitatively the geometric centers of the SNR shells. The obtained $t_{\rm r}$ ranges from 33 yr to $\approx 400$ kyr. We find that the two SNR ages, dynamical and plasma ages, are consistent with $t_{\rm r}$ within a factor of four, whereas the characteristic ages of the pulsars differ from $t_{\rm r}$ by more than a factor of four in some systems. Using the $t_{\rm r}$ summarized in this work, we present the initial spin periods of the associated pulsars, which are more strictly constrained than the previous works, as well.