Gaku Kawashima

Fast radio bursts (FRBs) provide a sensitive probe of ionized baryons through their dispersion measure (DM). In addition to slowly evolving cosmological terms, at least three repeaters now show clear secular DM-decrease episodes, FRB 20190520B, FRB 20220529A, and FRB 20121102 (the last with a two-stage trend: early mild rise and late decline), supporting a dense, dynamically evolving local environment. We adopt a forward-modeling approach and use time-dependent 1D supernova remnant (SNR) simulations for a young magnetar embedded in SN ejecta, combining single-star (SS) and binary-stripped (BS) progenitors with hydrodynamic and nonequilibrium ionization calculations to follow shock structure, ionization, and electron density. The shocked region contributes only limited DM (≲10 pc cm ⁻³ ), while the dominant time-varying component is the unshocked ejecta, whose early behavior follows DM ∝ t ^{− α} with α ≃ 1.8–1.9. Although shocked-region DM is small, shock-amplified magnetic fields can still generate substantial rotation measure (RM); in our shock-only RM framework, only the 11 M _⊙ SS model reproduces the FRB 20121102 RM evolution. BS progenitors generally yield smaller DM than SS models at fixed M _ZAMS , with composition-dependent mean molecular weights introducing nonmonotonic mass trends. Matching the observed d DM/ d t of FRB 20190520B, FRB 20220529A, and the late-stage slope of FRB 20121102, we infer local SNR DM contributions of ∼10 to a few × 10 ² pc cm ⁻³ . We also find that GHz escape is allowed in most models, with τ _ff = 1 typically reached by t _esc ≲ 70 yr; for weakly ionized ejecta, the source can be nearly transparent from very early times. These results support a young core-collapse supernova/SNR origin for a substantial fraction of DM _source and highlight that physically consistent local-environment modeling is essential for robust FRB cosmological DM inferences.

Core-collapse supernova remnants (CCSNRs) are crucial for understanding the final stages of massive star evolution, as they reflect the imprints of their progenitors’ preexplosion activities. However, the evolution of CCSNRs, particularly those originating from progenitors with high mass-loss rates—known as stripped-envelope supernova remnants (SESNRs)—remains poorly understood. This is largely due to the lack of comprehensive numerical models connecting progenitor stars to their remnants, especially in the context of binarity. In this study, we perform self-consistent simulations of CCSNRs from both single and binary progenitors, utilizing mass-loss histories and supernova ejecta profiles directly derived from stellar evolution and explosion calculations. Our models reveal significant differences in the circumstellar medium (CSM) structures between single and binary progenitors, which drive distinct SNR dynamics and spectral characteristics. We find that binary stripped-envelope progenitors tend to produce SNRs with more monotonic CSM profiles, resulting in smoother shock dynamics and less pronounced X-ray luminosity peaks compared to their single-star counterparts. Additionally, we introduce a new characteristic timescale, t _CSM , defined by the total mass lost by the progenitor. This timescale effectively scales the evolutionary phases of CCSNRs in complex CSM environments, thereby facilitating comparison of SESNRs. Given that observed elemental abundances in SNRs reflect the nucleosynthetic yields of the progenitor, our results highlight the importance of considering the dynamical state of SNRs when interpreting these abundances. This work provides a fiducial framework for future observational and theoretical studies of CCSNRs, particularly with regard to the impact of binary evolution.