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arXiv 2308.03395astro-ph.HE
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吸积脉冲星能量分辨脉冲轮廓:光谱特征的诊断工具

Energy-resolved pulse profiles of accreting pulsars: Diagnostic tools for spectral features

Carlo Ferrigno, Antonino D'Aì, Elena Ambrosi

AI总结:

提出从吸积X射线双星的能量分辨脉冲轮廓中提取光谱信息的方法,利用FFT确定脉冲分数并通过高斯轮廓搜索铁发射线和回旋共振散射特征,实现对特征位置和宽度的精确约束。

摘要:

我们提出了一种从以中子星自转周期折叠的能量分辨光变曲线(即脉冲轮廓)中提取光谱信息的方法,应用于吸积X射线双星。这些源的光谱有时以叠加在平滑连续谱上的特征为特征,例如铁发射线和回旋共振散射特征。我们在此探讨如何从脉冲轮廓的能量依赖变化中推导出对这些特征的定量约束。我们开发了一种稳健的方法,利用快速傅里叶变换(FFT)在每个能量选定区间内确定脉冲分数值,并在适当处截断至足以满意描述实际轮廓所需的谐波数。我们通过蒙特卡洛模拟采样总计1000个伪造轮廓来确定该值的不确定性。我们对能量分辨脉冲轮廓进行重新分箱,以确保在整个能量范围内保持恒定的最小信噪比。最后,我们使用现象学多项式模型表征能量分辨脉冲分数的依赖关系,并利用高斯线轮廓搜索与铁发射或回旋线光谱特征相对应的特征。我们将该方法应用于NuSTAR对知名吸积X射线脉冲星的代表性观测样本。我们表明,使用该方法可以表征脉冲分数光谱,并以与光谱结果相当的精度约束这些特征的位置和宽度。我们还探讨了如何将谐波分解、相关和滞后光谱用作探测和表征此类特征的额外探针。

英文摘要:

We introduce a method for extracting spectral information from energy-resolved light curves folded at the neutron star spin period (known as pulse profiles) in accreting X-ray binaries. Spectra of these sources are sometimes characterized by features superimposed on a smooth continuum, such as iron emission lines and cyclotron resonant scattering features. We address here the question on how to derive quantitative constraints on such features from energy-dependent changes in the pulse profiles. We developed a robust method for determining in each energy-selected bin the value of the pulsed fraction using the fast Fourier transform opportunely truncated at the number of harmonics needed to satisfactorily describe the actual profile. We determined the uncertainty on this value by sampling through Monte Carlo simulations a total of 1000 faked profiles. We rebinned the energy-resolved pulse profiles to have a constant minimum signal-to-noise ratio throughout the whole energy band. Finally we characterize the dependence of the energy-resolved pulsed fraction using a phenomenological polynomial model and search for features corresponding to spectral signatures of iron emission or cyclotron lines using Gaussian line profiles. We apply our method to a representative sample of NuSTAR observations of well-known accreting X-ray pulsars. We show that, with this method, it is possible to characterize the pulsed fraction spectra, and to constrain the position and widths of such features with a precision comparable with the spectral results. We also explore how harmonic decomposition, correlation, and lag spectra might be used as additional probes for detection and characterization of such features.

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