发表机构
State Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Chinese Academy of Sciences; ICRANet; ICRA, Dip. di Fisica, Sapienza Università di Roma; Università di Camerino; Al-Farabi Kazakh National University（中国科学院高能物理研究所粒子天体物理国家重点实验室; 中国科学院大学; 国际相对论天体物理中心网络; 罗马大学物理系ICRA小组; 卡梅里诺大学; 阿里-法拉比哈萨克国立大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过分析 GRB 240825A 的瞬时辐射三成分光谱、X 射线余辉衰减及 6.37 Hz 准周期振荡，对比磁星与黑洞两种中心引擎模型，发现六极磁星自转减慢模型能定量解释余辉，且磁星内部动力学可解释 QPO，综合观测支持长寿命磁星作为中心引擎。
AI 中文摘要
GRB 240825A 展示了前所未有的时间和光谱特征，这些特征约束了其内部引擎的性质：（1）瞬时辐射的三成分光谱，由 Band 函数连续谱、准热谱峰和硬 MeV 尾部组成；（2）X 射线余辉可用幂律衰减拟合，衰减指数为 $1.29 \pm 0.02$；（3）在 2.07-3.25 秒时间间隔内的 100-300 keV 能段中识别出 $6.37 \pm 0.05$ Hz 的准周期振荡（QPO），该振荡与光球辐射阶段相重合。我们比较了两种中心引擎候选体：（a）新生毫秒磁星，经历多极自转减慢、自由进动及其内部的整体磁弹振荡；（b）驱动 Blandford-Znajek 喷流的 Kerr 黑洞，受到 Lense-Thirring 盘进动的影响。原则上，两种通道都能重现观测到的 QPO 频率，但对能量学、时间演化以及振荡起源施加了不同的约束。我们首先证明，X 射线余辉可由六极磁星自转减慢模型定量重现，其初始自转周期为 $P_0 \simeq 1.38$ ms，表面磁场为 $B_{\rm hexa} \simeq 2.04 \times 10^{16}$ G。衰减指数衡量的是制动指数而非磁场多极性，不排除回落调控流，并使 $P_0$ 和 $B_{\rm hexa}$ 存在数倍的不确定性。在此情景下，恒星内部的磁或磁惯性动力学为 QPO 提供了合理解释，而无需引入极端恒星形变。尽管不能完全排除黑洞引擎，但 GRB 240825A 的瞬时辐射与余辉观测性质综合表明，其中心引擎更可能是长寿命磁星。
英文摘要
GRB 240825A shows unprecedented temporal and spectral features that constrain the properties of its inner engine: (1) a prompt emission three-component spectrum consisting of a Band function continuum, a quasi-thermal bump, and a hard MeV tail; and (2) an X-ray afterglow fitted by a power-law decay with index $1.29 \pm 0.02$; and (3) a $6.37 \pm 0.05$ Hz quasi-periodic oscillation (QPO) identified in the 100-300 keV band during the 2.07-3.25 s time interval, coinciding with the photospheric radiation phase. We compare two central-engine candidates: (a) a newborn millisecond magnetar undergoing multipolar spin-down, free precession, and global magnetoelastic oscillations of its interior; and (b) a Kerr black hole powering a Blandford-Znajek jet subject to Lense-Thirring disk precession. In principle, both channels can reproduce the observed QPO frequency but impose different constraints on the energetics, temporal evolution, and the origin of the oscillation. We first demonstrate that the X-ray afterglow is quantitatively reproduced by a hexapolar magnetar spin-down model with an initial spin period of $P_0 \simeq 1.38$ ms and a surface field of $B_{\rm hexa} \simeq 2.04 \times 10^{16}$ G. The decay index measures a braking index rather than the field multipolarity, does not exclude a fallback-regulated flow, and leaves $P_0$ and $B_{\rm hexa}$ uncertain by a factor of a few. In this scenario, magnetic or magnetoinertial dynamics of the star interior provide a plausible explanation of the QPO without invoking extreme stellar deformations. Although a black hole engine cannot be firmly excluded, the combined prompt and afterglow observational properties of GRB 240825A favor a long-lived magnetar central engine.
Comments12 pages, 2 figures; published in ApJ
Journal refAstrophys. J. 1009:163 (2026)
