吸积中子星中热康普顿化的指纹：回旋线与偏振中的等离子体-真空相互作用
Fingerprints of thermal Comptonization in accreting neutron stars. Plasma-vacuum interplay in cyclotron lines and polarisation
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中文总结 AI 辅助
本研究通过计算磁化康普顿化等离子体的偏振宽带谱，识别出吸积中子星中热康普顿化的能量相关各向异性特征，为探测中子星几何等提供互补诊断。
中文摘要 AI 辅助
来自吸积、强磁化中子星的X射线辐射及其脉冲相位变化可探测其磁场几何、自旋取向与辐射过程。辐射主要源自热点还是柱体，以及其特性是由整体康普顿化还是热康普顿化塑造，在不同光度范围内仍存在争议。本研究旨在区分本征辐射与可见度效应，识别热点和柱体中热康普顿化的特征可观测量。为此，我们未将模型限定于某一光度范围，推导了能量相关的束型与可观测量特征，重点关注回旋共振与偏振效应作为各向异性的示踪物。我们计算了宽参数范围内均匀自发射磁化康普顿化等离子体的角相关偏振宽带谱，包括基频回旋线。结合光弯曲与投影，我们获得了不同几何结构的相位相关流量，以及热点的观测线性偏振。束型随能量演化，驱动脉冲轮廓变化。在回旋共振附近，等离子体-真空相互作用产生窄中心束与侧瓣；其可见度在热点脉冲分数谱中产生与几何相关的下降、凸起及M形、W形结构，而柱体仅产生下降与凸起。热康普顿化回旋线无法可靠示踪等离子体温度；等离子体诱导的椭率与波段平均将观测到的软X射线线性偏振降低至0-30%。在典型X射线脉冲星吸积通道条件下，热康普顿化留下稳健的能量相关各向异性特征；能量分辨脉冲轮廓、脉冲分数谱与偏振因此为中子星几何、发射区形状与谱形成提供互补诊断。
英文摘要
X-ray emission from accreting, strongly magnetised neutron stars and its pulse-phase variability probe their magnetic-field geometry, spin orientation, and emission processes. Whether the radiation emerges mainly from a hot spot or column, and whether its properties are shaped by bulk or thermal Comptonization, remain debated across luminosity regimes. We aim to disentangle intrinsic emission from visibility effects and identify observables characteristic of thermal Comptonization in hot spots and columns. We therefore derived energy-dependent beam patterns and observable signatures without assigning the model to a luminosity regime, focusing on cyclotron-resonance and polarisation effects as tracers of anisotropy. To do so, we computed angle-dependent polarised broadband spectra, including the fundamental cyclotron line, for a homogeneous, self-emitting, magnetised Comptonizing plasma over a broad parameter range. Accounting for light bending and projection, we obtained phase-dependent fluxes for different geometries and, for hot spots, observed linear polarisation. The beam patterns evolve with energy, driving pulse-profile changes. Near the cyclotron resonance, plasma-vacuum interplay produces a narrow central beam and side petals. Their visibility creates geometry-dependent dips, bumps, and M- and W-shaped structures in hot-spot pulsed fraction spectra, but only dips and bumps for columns. Thermally Comptonized cyclotron lines do not reliably trace plasma temperature; plasma-induced ellipticity and band averaging reduce observed soft-X-ray linear polarisation to 0-30%. Under typical X-ray pulsar accretion-channel conditions, thermal Comptonization leaves robust energy-dependent anisotropic signatures. Energy-resolved pulse profiles, pulsed fraction spectra, and polarisation thus provide complementary diagnostics of neutron star geometry, emission-region shape, and spectral formation.
