New scenario of plasma evolution in IC 443

Most young and middle-aged supernova remnants (SNRs) exhibit an ionizing plasma (IP), an ionizing process following a shock-heated SNR gas. On the other hand, significant fractions of SNRs exhibit a recombining plasma (RP). The origin and the mechanisms of the RP, however, are not yet well understood. This paper proposes a new model that the RP follows after the IP process taken at the first epoch of the SNR evolution. Using the high-quality and wide-band (0.6–10 keV) spectrum of IC 443, we fitted it with a model of two RPs (two-RP model) plus a power law (PL) with an Fe i Kα line component. The ionization temperature in one RP monotonically increases from Ne–Ca, while that in the other RP shows a drastic increase from Cr–Ni. The origin and mechanism of the two-RP and PL with an Fe i Kα line components are possibly due to different evolution of two plasmas and ionization by low-energy cosmic rays.