标题： 掩食和吸积低质量X射线双星EXO 0748-676中0.58--2.44 Hz准周期振荡 显示英文标题

标题： A variable 0.58--2.44 Hz quasi-periodic oscillation in the eclipsing and dipping low-mass X-ray binary EXO 0748-676

摘要： 我们报告了用 Rossi X 射线时变探测器（RXTE）在吸积盘剪切和掩食低质量 X 射线双星 EXO 0748-676 的数据中发现的准周期振荡（QPO）。该 QPO 的频率在 0.58 至 2.44 Hz 之间，在几天的时间尺度上变化，均方根幅度在 8% 到 12% 之间，并且在持续辐射、吸收期间以及 I 型 X 射线爆发期间被检测到。在一次观测中，当计数率比平时高 2 到 3 倍时，未检测到 QPO。QPO 的强度在光子能量方面没有显著依赖性，并且与在持续辐射期间（包括吸收期间和 I 型 X 射线爆发期间）相同。在四次 X 射线爆发中的三次中观察到了频率偏移。我们认为，该 QPO 是由 Jonker 等人（1999 年）最近在 4U 1323-62 中发现的同一机制产生的。尽管确切机制尚不清楚，但很可能与这两个系统的高倾角有关。似乎围绕吸积盘的一个结构调制来自中心源的辐射是最有希望的机制。 显示英文摘要

摘要： We report the discovery of a quasi-periodic oscillation (QPO) in data obtained with the Rossi X-ray Timing Explorer of the dipping and eclipsing low-mass X-ray binary EXO 0748-676. The QPO had a frequency between 0.58 and 2.44 Hz changing on time scales of a few days, an rms amplitude between 8% and 12%, and was detected in the persistent emission, during dips and during type I X-ray bursts. During one observation, when the count rate was a factor 2 to 3 higher than otherwise, the QPO was not detected. The strength of the QPO did not significantly depend on photon energy, and is consistent with being the same in the persistent emission, both during and outside the dips, and during type I X-ray bursts. Frequency shifts were observed during three of the four X-ray bursts. We argue that the QPO is produced by the same mechanism as the QPO recently found by Jonker et al. (1999) in 4U 1323-62. Although the exact mechanism is not clear, it is most likely related to the high inclination of both systems. An orbiting structure in the accretion disc that modulates the radiation from the central source seems the most promising mechanism.