利用卡尔曼滤波器测量SXP 18.3的磁偶极矩与磁层涨落
Measuring the magnetic dipole moment and magnetospheric fluctuations of SXP 18.3 with a Kalman filter
AI总结：
针对吸积驱动脉冲星磁偶极矩无法从时间平均数据唯一推断的问题，提出用卡尔曼滤波器追踪涨落的方法，首次在SXP 18.3观测中验证成功，测得更准确的磁矩与辐射效率，还得到吸积率等隐变量估计，可用于后续脉冲星族群研究。
摘要：
处于磁离心平衡的吸积驱动脉冲星，其磁偶极矩$\mu$无法通过时间平均的脉冲周期和非周期X射线流量数据唯一推断，因为吸积的辐射效率$\eta_0$、恒星的质量、半径和距离均未知。若使用卡尔曼滤波器追踪脉冲周期和非周期X射线流量的涨落，便可规避与辐射效率相关的简并性，进而能唯一测量$\mu$，误差仅来源于质量、半径和距离的不确定性。本文首次在实际观测中成功验证了卡尔曼滤波器分析方法，所用数据来自Rossi X射线计时探测器对小麦哲伦星云中X射线暂现源SXP 18.3的常规监测观测。分析得到$\mu= 8.0^{+1.3}_{-1.2} \\, \times \\, 10^{30} \\, {\rm G \\, cm^3}$、$\eta_0 = 0.04^{+0.02}_{-0.01}$，而传统方法基于时间平均数据、假设$\eta_0=1$时推断的结果为$\mu= 5.0^{+1.0}_{-1.0} \times 10^{30} \\, {\rm G \\, cm^3}$。该分析还得到了两个隐状态变量的时间分辨估计值，即质量吸积率和盘-磁层边界处的麦克斯韦应力。本次验证的成功表明，未来可将卡尔曼滤波器分析应用于小麦哲伦星云及其他区域的吸积驱动脉冲星族群，以研究其磁矩和盘-磁层物理。
英文摘要：
The magnetic dipole moment $μ$ of an accretion-powered pulsar in magnetocentrifugal equilibrium cannot be inferred uniquely from time-averaged pulse period and aperiodic X-ray flux data, because the radiative efficiency $η_0$ of the accretion is unknown, as are the mass, radius, and distance of the star. The degeneracy associated with the radiative efficiency is circumvented, if fluctuations of the pulse period and aperiodic X-ray flux are tracked with a Kalman filter, whereupon $μ$ can be measured uniquely up to the uncertainties in the mass, radius, and distance. Here the Kalman filter analysis is demonstrated successfully in practice for the first time on Rossi X-ray Timing Explorer observations of the X-ray transient SXP 18.3 in the Small Magellanic Cloud, which is monitored regularly. The analysis yields $μ= 8.0^{+1.3}_{-1.2} \, \times \, 10^{30} \, {\rm G \, cm^3}$ and $η_0 = 0.04^{+0.02}_{-0.01}$, compared to $μ= 5.0^{+1.0}_{-1.0} \times 10^{30} \, {\rm G \, cm^3}$ as inferred traditionally from time-averaged data assuming $η_0=1$. The analysis also yields time-resolved estimates of two hidden state variables, the mass accretion rate and the Maxwell stress at the disk-magnetosphere boundary. The success of the demonstration confirms that the Kalman filter analysis can be applied in the future to study the magnetic moments and disk-magnetosphere physics of accretion-powered pulsar populations in the Small Magellanic Cloud and elsewhere.
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