X-ray polarisation signatures in bombarded magnetar atmospheres

IF 4.7 3区 物理与天体物理 Q1 ASTRONOMY & ASTROPHYSICS Monthly Notices of the Royal Astronomical Society Pub Date : 2024-09-18 DOI:10.1093/mnras/stae2163
Ruth M E Kelly, Denis González-Caniulef, Silvia Zane, Roberto Turolla, Roberto Taverna
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Abstract

Magnetars are neutron stars that host huge, complex magnetic fields which require supporting currents to flow along the closed field lines. This makes magnetar atmospheres different from those of passively cooling neutron stars because of the heat deposited by backflowing charges impinging on the star surface layers. This particle bombardment is expected to imprint the spectral and, even more, the polarisation properties of the emitted thermal radiation. We present solutions for the radiative transfer problem for bombarded plane-parallel atmospheres in the high magnetic field regime. The temperature profile is assumed a priori, and selected in such a way to reflect the varying rate of energy deposition in the slab (from the impinging currents and/or from the cooling crust). We find that thermal X–ray emission powered entirely by the energy released in the atmosphere by the magnetospheric back–bombardment is linearly polarised and X-mode dominated, but its polarisation degree is significantly reduced (down to 10%–50%) when compared with that expected from a standard atmosphere heated only from the cooling crust below. By increasing the fraction of heat flowing in from the crust the polarisation degree of the emergent radiation increases, first at higher energies (∼10 keV) and then in the entire soft X-ray band. We use our models inside a ray-tracing code to derive the expected emission properties as measured by a distant observer and compare our results with recent IXPE observations of magnetar sources.
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轰击磁星大气中的 X 射线极化特征
磁星是中子星,它拥有巨大而复杂的磁场,需要支持电流沿着封闭的磁场线流动。这使得磁星大气层与被动冷却的中子星大气层不同,因为逆流电荷撞击到恒星表层会沉积热量。这种粒子轰击预计会影响辐射热的光谱特性,甚至偏振特性。我们提出了高磁场条件下轰击平面平行大气的辐射传递问题的解决方案。温度曲线是先验假定的,其选择方式反映了板坯中能量沉积的变化率(来自撞击流和/或来自冷却地壳)。我们发现,完全由大气层中磁层反轰击释放的能量驱动的热 X 射线辐射是线性偏振的,以 X 模式为主,但与仅由下面冷却的地壳加热的标准大气层的辐射相比,其偏振程度显著降低(降至 10%-50%)。通过增加从地壳流入的热量,出现的辐射的极化程度会增加,首先是在较高能量(∼10 keV),然后是整个软 X 射线波段。我们在射线追踪代码中使用我们的模型,推导出远处观测者测量到的预期辐射特性,并将我们的结果与最近对磁星源的 IXPE 观测结果进行比较。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
CiteScore
9.10
自引率
37.50%
发文量
3198
审稿时长
3 months
期刊介绍: Monthly Notices of the Royal Astronomical Society is one of the world''s leading primary research journals in astronomy and astrophysics, as well as one of the longest established. It publishes the results of original research in positional and dynamical astronomy, astrophysics, radio astronomy, cosmology, space research and the design of astronomical instruments.
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