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arXiv 0801.0909astro-ph
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吸积动力毫秒脉冲星XTE J1807-294的精确轨道参数和反常相位变化

Precise Orbital Parameters and Anomalous Phase Variations of the Accretion-powered Millisecond Pulsar XTE J1807-294

Y. Chou, Y. Chung, C. P. Hu, T. C. Yang

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26 pages, 8 figures, accepted by ApJ
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摘要：

本文报道了{ \it Rossi X射线定时探测器}对第四颗被发现的吸积动力毫秒脉冲星XTE J1807-294在2003年爆发期间的脉冲变化分析结果。仅在$\sim$ 150 d观测中的前$\sim$ 90 d中显著检测到脉动。脉冲相位变化太复杂，不能用轨道运动加简单的多项式模型来描述。对不含开普勒轨道的150 s脉冲相位进行趋势去除，得到了$P_{orb}=40.073601(8)$ min和${\it a_x}\sin {\it i}=4.823(5)$ lt-ms的精确轨道参数。二元重心校正后的脉冲相位显示出平滑的演化和明显的负相移，与光变曲线上看到的耀斑和分数脉冲幅度的增强相一致。第一个$\sim$ 60 d数据的非耀斑脉冲相位被很好地描述为四阶多项式，这意味着在爆发开始时，中子星在第一个$\sim$ 60 d期间以$\dot ν=(1.7\pm0.3) \times 10^{-13}$ Hz/s的速率旋转。对于非耀斑脉冲相位，在2至20 keV之间检测到高达$\sim$ 500 $μs$（$\sim$ 10%周期）的显著软相位滞后。我们的结论是，异常相移不太可能是由于吸积扭矩，但可能是由于"热点“在中子星的表面上移动。

英文摘要：

This study reports pulse variation analysis results for the forth discovered accretion-powered millisecond pulsar XTE J1807-294 during its 2003 outburst observed by {\it Rossi X-ray Timing Explorer}. The pulsation is significantly detected only in the first $\sim$90d out of $\sim$150d observations. The pulse phase variation is too complex to be described as an orbital motion plus a simple polynomial model. The precise orbital parameters with $P_{orb}=40.073601(8)$ min and ${\it a_x}\sin {\it i}=4.823(5)$ lt-ms were obtained after applying the trend removal to the daily observed 150s segments pulse phases folded with a constant spin frequency without Keplerian orbit included. The binary barycenter corrected pulse phases show smooth evolution and clear negative phase shifts coincident with the flares seen on the light curve and the enhancements of fractional pulse amplitude. The non-flare pulse phases for the first $\sim$60d data are well described as a fourth order polynomial implying that the neutron star was spun-up during the first $\sim$60d with a rate $\dot ν=(1.7\pm0.3) \times 10^{-13}$ Hz/s at the beginning of the outburst. Significant soft phase lags up to $\sim$500 $μs$ ($\sim$10% cycle) between 2 to 20 keV were detected for the nonflare pulse phases. We conclude that the anomalous phase shifts are unlikely due to the accretion torque but could result from the ``hot spot'' moving on the surface of neutron star.

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