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arXiv 2004.09541astro-ph.HE
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磁星耀斑的共振回旋散射光谱修正

Spectral Modification of Magnetar Flares by Resonant Cyclotron Scattering

Shotaro Yamasaki, Yuri Lyubarsky, Jonathan Granot, Ersin Gogus

摘要:

研究了磁星耀斑的共振回旋散射光谱修正。在高能耀斑期间,从恒星表面附近的磁捕获火球发射的光子应该与磁层电子或正电子共振相互作用。我们通过一个简单的思想实验表明,这样的散射粒子预计将沿着封闭的磁场线以温和的相对论速度移动,这将使入射光子能量由于多普勒效应而略有偏移。我们开发了一个玩具模型的光谱修改由一个单一的RCS,它结合了一个现实的种子光子光谱从被困的火球和粒子的速度场,这是独特的耀斑磁层。我们表明,我们的光谱模型可以有效地由一个单一的参数,火球的有效温度,这使我们能够以较低的计算成本,以适应观察到的光谱。我们证明,我们的单散射模型是在显着的一致性与斯威夫特/BAT数据的中间耀斑从SGR 1900+14,相应的有效火球温度为$T_{\rm eff}=6$ - $7$ keV,而BeppoSAX/GRBM数据的巨耀斑从同一来源可能需要更精细的模型,包括多重散射的影响。然而,由于没有标准的物理动机模型的磁星耀斑光谱,我们的模型可能是一个有用的工具来研究磁星爆发,揭示隐藏的属性的耀斑磁层。

英文摘要:

Spectral modification of energetic magnetar flares by resonant cyclotron scattering (RCS) is considered. During energetic flares, photons emitted from the magnetically-trapped fireball near the stellar surface should resonantly interact with magnetospheric electrons or positrons. We show by a simple thought experiment that such scattering particles are expected to move at mildly relativistic speeds along closed magnetic field lines, which would slightly shift the incident photon energy due to the Doppler effect. We develop a toy model for the spectral modification by a single RCS that incorporates both a realistic seed photon spectrum from the trapped fireball and the velocity field of particles, which is unique to the flaring magnetosphere. We show that our spectral model can be effectively characterized by a single parameter; the effective temperature of the fireball, which enables us to fit observed spectra with low computational cost. We demonstrate that our single scattering model is in remarkable agreement with Swift/BAT data of intermediate flares from SGR 1900+14, corresponding to effective fireball temperatures of $T_{\rm eff}=6$-$7$ keV, whereas BeppoSAX/GRBM data of giant flares from the same source may need more elaborate models including the effect of multiple scatterings. Nevertheless, since there is no standard physically-motivated model for magnetar flare spectra, our model could be a useful tool to study magnetar bursts, shedding light on the hidden properties of the flaring magnetosphere.

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