NANOGrav 15年数据集：引力波背景的分段幂律重建
The NANOGrav 15 yr Data Set: Piecewise Power-Law Reconstruction of the Gravitational-Wave Background
AI总结：
NANOGrav 15年数据集通过分段幂律模型重建引力波背景信号，以确定其来源。
摘要：
NANOGrav 15年（NG15）数据集提供了纳赫兹频率范围内的引力波背景（GWB）信号的证据，该信号预计可能源于宇宙中螺旋进动的超大质量黑洞双星或早期宇宙的新粒子物理现象。要确定NG15信号的来源，需要对其频率谱进行精确重建。本文基于一种分段幂律（PPL）假设，提供对NG15信号的频谱特征进行描述。我们的PPL重建比标准的常数幂律模型更灵活，后者仅用两个参数描述GWB谱：幅度A和频谱指数gamma。同时，它比自由频谱模型更接近物理上真实的GWB谱，特别是那些具有宇宙学起源的谱。因为后者允许在不同频率区间内任意变化GWB幅度。我们的NG15信号PPL重建依赖于具有固定内部节点数（即常数幂律、折线幂律、双折线幂律等）的个体PPL模型，这些模型最终通过贝叶斯模型平均结合。我们的分析所产生的数据产品为快速重拟谱GWB模型提供了基础。
英文摘要：
The NANOGrav 15-year (NG15) data set provides evidence for a gravitational-wave background (GWB) signal at nanohertz frequencies, which is expected to originate either from a cosmic population of inspiraling supermassive black-hole binaries or new particle physics in the early Universe. A firm identification of the source of the NG15 signal requires an accurate reconstruction of its frequency spectrum. In this paper, we provide such a spectral characterization of the NG15 signal based on a piecewise power-law (PPL) ansatz that strikes a balance between existing alternatives in the literature. Our PPL reconstruction is more flexible than the standard constant-power-law model, which describes the GWB spectrum in terms of only two parameters: an amplitude A and a spectral index gamma. Concurrently, it better approximates physically realistic GWB spectra -- especially those of cosmological origin -- than the free spectral model, since the latter allows for arbitrary variations in the GWB amplitude from one frequency bin to the next. Our PPL reconstruction of the NG15 signal relies on individual PPL models with a fixed number of internal nodes (i.e., constant power law, broken power law, doubly broken power law, etc.) that are ultimately combined in a Bayesian model average. The data products resulting from our analysis provide the basis for fast refits of spectral GWB models.
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