PSR J0108 $-$ 1431中多极表面磁场证据的评估
Evaluating the Evidence of Multipolar Surface Magnetic Field in PSR J0108$-$1431
摘要：
PSR J0108 $-$ 1431是一颗古老的脉冲星，其X射线辐射预计有来自极冠的热分量和来自磁层的非热分量。虽然相位积分光谱与用光子指数$Γ=2.9$的幂律（PL）建模的单个非热分量拟合得最好，但是X射线脉冲轮廓确实显示存在相位分离的热分量和非热分量。从远离X射线峰的旋转相位的一半提取的光谱与单个黑体（BB）或中子星大气（NA）模型很好地拟合，而从相位范围的其余部分提取的光谱由PL主导。根据贝叶斯分析，估计的BB面积小于偶极磁场的预期极帽面积，概率为86%，而NA模型的面积估计值较大，概率为80%。由于热辐射模型的模糊性，极冠面积不能可靠地估计，因此不能用于理解表面磁场的性质。相反，我们可以从脉冲星的热X射线峰值和射电发射峰值之间的不对准来推断多极磁场的存在。对于J0108 $-$ 1431，我们估计了热极冠发射峰和无线电发射峰之间的相位偏移$Δϕ> 0.1$，并认为这是最好的解释多极表面磁场的存在。
英文摘要：
PSR J0108$-$1431 is an old pulsar where the X-ray emission is expected to have a thermal component from the polar cap and a non-thermal component from the magnetosphere. Although the phase-integrated spectra are fit best with a single non-thermal component modeled with a power-law (PL) of photon index $Γ=2.9$, the X-ray pulse profiles do show the presence of phase-separated thermal and non-thermal components. The spectrum extracted from half the rotational phase away from the X-ray peak fits well with either a single blackbody (BB) or a neutron star atmosphere (NA) model, whereas, the spectrum from the rest of the phase range is dominated by a PL. From Bayesian analysis, the estimated BB area is smaller than the expected polar cap area for a dipolar magnetic field with a probability of 86% whereas the area estimate from the NA model is larger with a probability of 80%. Due to the ambiguity in the thermal emission model, the polar cap area cannot be reliably estimated and hence cannot be used to understand the nature of the surface magnetic field. Instead, we can infer the presence of multipolar magnetic field from the misalignment between the pulsar's thermal X-ray peak and the radio emission peak. For J0108$-$1431, we estimated a phase-offset $Δϕ> 0.1$ between the thermal polar cap emission peak and the radio emission peak and argue that this is best explained by the presence of a multipolar surface magnetic field.
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