Probing the Dispersion and Rotation Measure Contributions from Supernova Remnants in Fast Radio Burst Source Environments with 1D SNR Simulation

Le résumé fourni par la source

Abstract 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.

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