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arXiv 1712.09643astro-ph.HE
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高磁化中子星的共振逆康普顿散射谱

Resonant Inverse Compton Scattering Spectra from Highly-magnetized Neutron Stars

Zorawar Wadiasingh, Matthew G. Baring, Peter L. Gonthier, Alice K. Harding

摘要:

在近十颗磁星中观测到了能量在10 keV和$\sim 150$ keV之间的硬的、非热的、持续的脉冲X射线辐射。对于这种发射的内磁层模型,超相对论电荷对软热光子的共振逆康普顿散射是最有效的产生机制。我们提出了角度依赖的上散射光谱和脉冲强度地图的非冷却,相对论电子注入磁星磁层的内部区域,计算使用碰撞积分场循环。我们的计算采用了一种新的配方的QED康普顿散射截面在强磁场,是物理正确的治疗重要的自旋相关效应的回旋共振,从而产生正确的光子谱。光谱截止能量对观察者观察几何形状、电子洛伦兹因子和散射运动学的选择很敏感。我们发现,能量为$\lesssim 15$兆电子伏的电子将发出大部分低于250千电子伏的辐射,与磁星硬X射线尾的推断周转一致。更多的高能电子仍然发射主要低于1兆电子伏,除了观察视角采样场线切线。脉冲轮廓可以是单峰或双峰,这取决于观察几何形状、发射位置和观察到的能带。磁对的产生和光子分裂将使光谱衰减到硬X射线能量,抑制费米LAT带中的信号。共振康普顿光谱是强烈极化的,这表明硬X射线偏振测量仪器,如X-Calibur,或未来的康普顿望远镜,可以证明是约束模型几何和物理的核心。

英文摘要:

Hard, non-thermal, persistent pulsed X-ray emission extending between 10 keV and $\sim 150$ keV has been observed in nearly ten magnetars. For inner-magnetospheric models of such emission, resonant inverse Compton scattering of soft thermal photons by ultra-relativistic charges is the most efficient production mechanism. We present angle-dependent upscattering spectra and pulsed intensity maps for uncooled, relativistic electrons injected in inner regions of magnetar magnetospheres, calculated using collisional integrals over field loops. Our computations employ a new formulation of the QED Compton scattering cross section in strong magnetic fields that is physically correct for treating important spin-dependent effects in the cyclotron resonance, thereby producing correct photon spectra. The spectral cut-off energies are sensitive to the choices of observer viewing geometry, electron Lorentz factor, and scattering kinematics. We find that electrons with energies $\lesssim 15$ MeV will emit most of their radiation below 250 keV, consistent with inferred turnovers for magnetar hard X-ray tails. More energetic electrons still emit mostly below 1 MeV, except for viewing perspectives sampling field line tangents. Pulse profiles may be singly- or doubly-peaked dependent upon viewing geometry, emission locale, and observed energy band. Magnetic pair production and photon splitting will attenuate spectra to hard X-ray energies, suppressing signals in the Fermi-LAT band. The resonant Compton spectra are strongly polarized, suggesting that hard X-ray polarimetry instruments such as X-Calibur, or a future Compton telescope, can prove central to constraining model geometry and physics.

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