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arXiv 0903.0580astro-ph.HE
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吸积脉冲星XMMU J054134的脉冲热辐射

Pulsed thermal emission from the accreting pulsar XMMU J054134.7-682550

A. Manousakis, R. Walter, M. Audard, T. Lanz

摘要:

目标。在几个Be/X射线双星中已经检测到软X射线过量,并将其解释为内部吸积盘中硬X射线再处理的特征。位于大麦哲伦星系的XMMU J054134.7-682550系统,在2007年8月有一次巨大的II型爆发。这个系统的几何形状可以通过研究软过量发射对硬X射线脉冲的响应来理解。方法.我们分析了一系列的同时观测获得XMM-牛顿/EPIC-MOS和RXTE/PCA,以获得光谱和时间特性的系统,之前,期间和之后的巨大爆发。进行了光谱拟合,并进行了时序分析。分析了光谱变化、自旋周期演化和能量依赖的脉冲形状。结果爆发(L_X = 3* 10^38 erg/s \approx L_EDD)光谱可以成功地用截止幂律、冷盘发射、热黑体和回旋吸收线来模拟。磁场和磁层半径可以被约束。内吸积盘的厚度加宽到75公里宽。热黑体组件的正弦调制表明,大部分的硬X射线发射优先沿磁赤道发射。脉冲星的自旋周期在爆发期间非常显著地减小。这与各种各样的中子星状态方程是一致的,并表明一个非常高的吸积率。

英文摘要:

Aims. Soft X-ray excesses have been detected in several Be/X-ray binaries and interpreted as the signature of hard X-ray reprocessing in the inner accretion disk. The system XMMU J054134.7-682550, located in the LMC, featured a giant Type II outburst in August 2007. The geometry of this system can be understood by studying the response of the soft excess emission to the hard X-ray pulses. Methods. We have analyzed series of simultaneous observations obtained with XMM-Newton/EPIC-MOS and RXTE/PCA in order to derive spectral and temporal characteristics of the system, before, during and after the giant outburst. Spectral fits were performed and a timing analysis has been carried out. Spectral variability, spin period evolution and energy dependent pulse shapes are analysed. Results. The outburst (L_X = 3* 10^38 erg/s \approx L_EDD) spectrum could be modeled successfully using a cutoff powerlaw, a cold disk emission, a hot blackbody, and a cyclotron absorption line. The magnetic field and magnetospheric radius could be constrained. The thickness of the inner accretion disk is broadened to a width of 75 km. The hot blackbody component features sinusoidal modulations indicating that the bulk of the hard X-ray emission is emitted preferentially along the magnetic equator. The spin period of the pulsar decreased very significantly during the outburst. This is consistent with a variety of neutron star equations of state and indicates a very high accretion rate.

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