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arXiv 0910.5546astro-ph.HEastro-ph.SR
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低质量X射线双星EXO 0748-676中552 Hz爆发振荡的发现

Discovery of a 552 Hz burst oscillation in the low-mass X-ray binary EXO 0748-676

Duncan K. Galloway, Jinrong Lin, Deepto Chakrabarty, Jacob M. Hartman

摘要:

我们报告了Rossi X射线定时探测器在2007年1月和12月从吸积中子星EXO 0748-676观测到的两个I型(热核)X射线爆发的上升阶段中552 Hz的脉动。分数振幅为15%(rms)。每次爆发的动态功率密度谱显示,频率增加约。1-2 Hz,同时存在振荡。频率漂移、探测的高度显著性以及在相隔11个月的两次爆发中测得的几乎相同的信号频率,证实了这一信号是一种爆发振荡,与迄今为止在其他13个来源中发现的信号类似。因此,我们得出结论,EXO 0748-676中的自旋频率在552 Hz的几Hz之内,而不是Villarreal & Strohmayer(2004)早期信号检测所建议的45 Hz。因此,多普勒展宽一定会显著影响中子星表面产生的光谱特征,因此先前报道的XMM-牛顿光谱的窄吸收特征不可能出现在那里。先前报道的45 Hz振荡和X射线吸收线的起源现在还不确定。

英文摘要:

We report the detection of pulsations at 552 Hz in the rising phase of two type-I (thermonuclear) X-ray bursts observed from the accreting neutron star EXO 0748-676 in 2007 January and December, by the Rossi X-ray Timing Explorer. The fractional amplitude was 15% (rms). The dynamic power density spectrum for each burst revealed an increase in frequency of approx. 1-2 Hz while the oscillation was present. The frequency drift, the high significance of the detections and the almost identical signal frequencies measured in two bursts separated by 11 months, confirms this signal as a burst oscillation similar to those found in 13 other sources to date. We thus conclude that the spin frequency in EXO 0748-676 is within a few Hz of 552 Hz, rather than 45 Hz as was suggested from an earlier signal detection by Villarreal & Strohmayer (2004). Consequently, Doppler broadening must significantly affect spectral features arising from the neutron star surface, so that the narrow absorption features previously reported from an XMM-Newton spectrum could not have arisen there. The origin of both the previously reported 45 Hz oscillation and the X-ray absorption lines is now uncertain.

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