The giant outburst of EXO 2030+375,Astronomy & Astrophysics

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The giant outburst of EXO 2030+375
Astronomy & Astrophysics ( IF 5.4 ) Pub Date : 2024-08-22 , DOI: 10.1051/0004-6361/202348595
R. Ballhausen , P. Thalhammer , P. Pradhan , E. Sokolova-Lapa , J. Stierhof , K. Pottschmidt , J. Wilms , J. B. Coley , P. Kretschmar , F. Fürst , P. Becker , B. West , C. Malacaria , M. T. Wolff , R. Rothschild , R. Staubert

In 2021, the high-mass X-ray binary EXO 2030+375 underwent a giant X-ray outburst, the first since 2006, that reached a peak flux of ∼600 mCrab (3–50 keV). The goal of this work is to study the spectral evolution over the course of the outburst, search for possible cyclotron resonance scattering features (CRSFs), and to associate spectral components with the emission pattern of the accretion column. We used broadband spectra taken with the Nuclear Spectroscopic Telescope Array (NuSTAR), the Neutron Star Interior Composition Explorer (NICER), and Chandra near the peak and during the decline phase of the outburst. We describe the data with established empirical continuum models and perform pulse-phase-resolved spectroscopy. We compare the spectral evolution with pulse phase using a proposed geometrical emission model. We find a significant spectral hardening toward lower luminosity, a behavior that is expected for super-critical sources. The continuum shape and evolution cannot be described by a simple power-law model with exponential cutoff; it requires additional absorption or emission components. We can confirm the presence of a narrow absorption feature at ∼10 keV in both NuSTAR observations. The absence of harmonics puts into question the interpretation of this feature as a CRSF. The empirical spectral components cannot be directly associated with identified emission components from the accretion column.

中文翻译：

EXO 2030+375的巨型爆发

2021年，高质量X射线双星EXO 2030+375经历了一次巨大的X射线爆发，这是自2006年以来的第一次，峰值通量达到~600 mCrab（3-50 keV）。这项工作的目标是研究爆发过程中的光谱演化，寻找可能的回旋共振散射特征（CRSF），并将光谱成分与吸积柱的发射模式相关联。我们使用了核光谱望远镜阵列（NuSTAR）、中子星内部成分探测器（NICER）和钱德拉在爆发峰值附近和衰退阶段拍摄的宽带光谱。我们用已建立的经验连续模型描述数据并执行脉冲相位分辨光谱。我们使用提出的几何发射模型将光谱演变与脉冲相位进行比较。我们发现显着的光谱硬化朝向较低的光度，这是超临界光源所预期的行为。连续体的形状和演化不能用具有指数截止的简单幂律模型来描述；它需要额外的吸收或发射组件。我们可以确认在两次 NuSTAR 观测中都存在~10 keV 处的窄吸收特征。由于没有谐波，因此将此功能解释为 CRSF 受到质疑。经验光谱分量不能直接与来自吸积柱的已识别发射分量相关联。