IIb型超新星SN 2024iss的射电约束对其星周环境的研究
Radio Constraints on the Circumstellar Environment of the Type IIb Supernova SN 2024iss
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中文总结 AI 辅助
通过对IIb型超新星SN 2024iss的射电监测，结合SSA建模分析，发现其存在速度 excess，提出其前身星周围有致密CSM，揭示其爆炸前不久质量损失历史复杂非稳态。
中文摘要 AI 辅助
IIb型超新星的前身星性质存在多样性，射电观测为探测其爆炸前不久的质量损失历史提供了独特手段。我们利用日本甚长基线干涉测量网络（VLBI Network）的单基线，对近邻IIb型超新星SN 2024iss开展了6.9GHz和8.4GHz两个频率、覆盖其发现后约1年的监测。射电观测在其爆炸后10天和23天检测到了辐射，后续多个观测时段未检测到辐射。基于峰值射电光度和峰值时间，SN 2024iss的射电性质与致密包层事件高度相似。通过同步自吸收（SSA）建模，对于致密前身星的风速度为100km/s，我们估算出前身星的质量损失率约为2.5×10^-6 M☉/年。此外，SSA分析得出平均膨胀速度V_sh≈3.3×10^4 km/s，该速度超过自相似解推导的理论激波速度约2.4倍；即使采用保守的峰值时间上限，SSA推导的速度仍比理论预期大至少1.7倍。为解释这一速度 excess，我们提出前身星周围存在受限的致密星周物质（CSM），该受限CSM中的激波出射可能加速了前向激波，表明其爆炸前不久的质量损失历史极为复杂且非稳态。
英文摘要
Type~IIb supernovae exhibit diverse progenitor properties, and radio observations offer a unique probe of their mass-loss histories shortly before the explosion. We present Japanese VLBI Network single-baseline monitoring of the nearby Type IIb SN 2024iss at 6.9 and 8.4 GHz, spanning approximately one year after its discovery. Our radio observations have detected its emission at 10 and 23 days after the explosion, with subsequent epochs yielding non-detections. Based on the peak radio luminosity and peak time, SN 2024iss exhibits radio properties highly comparable to those of compact-envelope events. Using a synchrotron self-absorption (SSA) modeling, we estimate a progenitor mass-loss rate of $\dot{M} \approx 2.5 \times 10^{-6}\>M_{\odot}\>{\rm yr^{-1}}$ for a compact progenitor wind velocity of $100 \>{\rm km\>s^{-1}}$. Furthermore, our SSA analysis yields a mean expansion velocity of $V_{\rm sh} \approx 3.3 \times 10^4\>{\rm km\>s^{-1}}$, which exceeds the theoretical shock velocity derived from the self-similar solution by a factor of $\sim 2.4$. Even for the conservative upper-bound peak time, the SSA-derived velocity remains larger than the theoretical expectation by a factor of $\gtrsim 1.7$. To explain this velocity excess, we propose the presence of a confined, dense circumstellar matter (CSM) surrounding the progenitor. The shock emergence from this confined CSM may have accelerated the forward shock, pointing to a highly complex and non-steady mass-loss history shortly before the explosion.
