标题： X射线脉冲星4U 1626-67在最近高通量状态下的光谱和时间过渡 显示英文标题

标题： Spectral and temporal transition in the X-ray pulsar 4U 1626-67 during the recent high flux state

摘要： 4U 1626-67 是一个吸积驱动的 X 射线脉冲星，在数小时的时间尺度上显示出非常稳定的 X 射线光度，并在几年的时间尺度上表现出渐进的强度变化。与其他高磁场双星 X 射线脉冲星不同，中子星的自转加速或减速率在数年内也非常稳定。在这里，我们报告了在 4U 1626-67 长期 RXTE-ASM 光变曲线中 X 射线强度的突然增加。类似地，Swift-BAT 光变曲线中也报告了 X 射线流量的增强。我们利用来自 Rossi X 射线时变探测器上的比例计数阵列获得的数据，研究了 4U 1626-67 在其最近增强流量发射状态下的光谱和时间特征。X 射线流量的增加持续了大约 100 天，并似乎有两个流量增强阶段。我们在当前高流量状态下检测到了源的光谱和时间变化的相关性。在增强流量状态下观察到软 X 射线光子发射有显著过剩，这与脉冲星在 1990 年之前自转加速时期的能量谱相似。4U 1626-67 是一个独特的吸积驱动 X 射线脉冲星，在过去约 20 年中一直稳定地观测到准周期振荡。但在最近的观测中，我们没有检测到以前观测中出现的 QPO。相反，我们报告了在 130 mHz 峰值的翼部显著扩展以及低质量 X 射线双星系统 4U 1626-67 的功率谱连续谱形状的变化。这些结果表明，流量增强不仅仅是质量吸积率的简单增加，而且在中子星附近也发生了吸积几何结构的变化。 显示英文摘要

摘要： 4U 1626-67 is an accretion powered X-ray pulsar that shows remarkably stable X-ray luminosity above hours timescale and gradual intensity variation on a few years timescale. Unlike other high magnetic field binary X-ray pulsars, the spin-up or spindown rate of the neutron star is also very stable upto several years. Here we report a sudden increase in the X-ray intensity in the long term RXTE-ASM light curve of 4U 1626-67. Similar enhancement in the X-ray flux has also been reported from the Swift-BAT light curve. We have investigated the spectral and timing features of 4U 1626-67 during its recent state of enhanced ux emission with data obtained from the Proportional Counter Array onboard the Rossi X-ray Timing Explorer. The increase in the X-ray flux took place over a long period of about 100 days and there appears to be two episodes of flux enhancement. We have detected a correlated spectral and temporal change in the source during the present high ux state. A significant excess in soft X-ray photon emission is observed during the enhanced ux state, which is similar to the energy spectrum obtained during the spin-up era of the pulsar before 1990. 4U 1626-67 is a unique accretion powered X-ray pulsar in which quasi periodic oscillations have been consistently observed over the past ~20 years. But during the recent observations, we did not detect a QPO at frequencies as observed in earlier observations. Instead, we report of detection of significant broadening in the wings of the 130 mHz peak and a change in the shape of the continuum of the power spectrum of the low mass X-ray binary system 4U 1626-67. These results indicate that the flux enhancement is not a simple case of increased mass accretion rate, but there is also a change in the accretion geometry in the vicinity of the neutron star.