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arXiv 1302.6464astro-ph.HE
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低质量X射线双星4U 1608- 52和4U 1636- 53的千赫准周期振荡的时滞

Time lags of the kilohertz quasi-periodic oscillations in the low-mass X-ray binaries 4U 1608--52 and 4U 1636--53

M. G. B. de Avellar, M. Méndez, A. Sanna, J. E. Horvath

摘要:

我们利用RXTE数据研究了NS LMXB 4U 1608-52和4U 1636-53中kHz QPO的傅里叶时间滞后和固有相干性的能量和频率依赖性。在这两个源中,我们证实了较低kHz QPO的10-100 μs的能量依赖性软滞后。我们还发现,上kHz QPO的时间滞后与能量无关,并且与下kHz QPO的软滞后不一致。较低kHz QPO的固有相干性从5到12 keV保持恒定在0.6,然后下降到零,而对于较高kHz QPO,固有相干性在整个能量范围内与零一致。上kHz QPO的固有相干性在QPO的整个频率范围内与零一致,除了在4U 1636-53中在~780 Hz处增加到0.13。在4U 1636-53中,对于较低kHz的QPO,在500-850 Hz的QPO频率范围内,4-12 keV的光子滞后于12-20 keV的光子25 μs,在较高频率下,滞后减小到15 μs。在4U 1608-52中,较低kHz QPO的软滞后保持恒定在40 μs。在4U 1636-53中,对于较高kHz的QPO,12-20 keV的光子滞后于4-12 keV的光子11 +/- 3 μs,与QPO频率无关;我们在4U 1608-52中发现了较高kHz QPO的时间滞后的一致结果。在4U 1636-53和4U 1608-52中,较低kHz QPO的固有相干性分别从600 Hz处的~0-0.4增加到800 Hz处的1和0.6。在4U 1636-53中,它在920 Hz时降低到0.5,而在4U 1608-52中,我们没有高于800 Hz的数据。我们讨论了我们的结果的情况下,软滞后是由于反射的吸积盘或向上/向下散射的热介质靠近中子星。最后,我们探讨了这两个源中kHz QPO的时间滞后和内在相干性以及QPO的幅度和品质因数之间的联系。

英文摘要:

(abridged) We studied the energy and frequency dependence of the Fourier time lags and intrinsic coherence of the kHz QPOs in the NS LMXBs 4U 1608-52 and 4U 1636-53 using RXTE data. In both sources we confirmed energy-dependent soft lags of 10-100 μs for the lower kHz QPO. We also found that the time lags of the upper kHz QPO are independent of energy and inconsistent with the soft lags of the lower kHz QPO. The intrinsic coherence of the lower kHz QPO remains constant at 0.6 from 5 to 12 keV, and then drops to zero, while for the upper kHz QPO the intrinsic coherence is consistent with zero across the full energy range. The intrinsic coherence of the upper kHz QPO is consistent with zero over the full frequency range of the QPO, except in 4U 1636-53 at ~780 Hz where it increases to 0.13. In 4U 1636-53, for the lower kHz QPO the 4-12 keV photons lag the 12-20 keV ones by 25 μs in the QPO frequency range 500-850 Hz, with the lags decreasing to 15 μs at higher frequencies. In 4U 1608-52 the soft lags of the lower kHz QPO remain constant at 40 μs. In 4U 1636-53, for the upper kHz QPO the 12-20 keV photons lag the 4-12 keV ones by 11 +/- 3 μs, independent of QPO frequency; we found consistent results for the time lags of the upper kHz QPO in 4U 1608-52. The intrinsic coherence of the lower kHz QPO increases from ~0-0.4 at 600 Hz to 1 and 0.6 at 800 Hz in 4U 1636-53 and 4U 1608-52, respectively. In 4U 1636-53 it decreases to 0.5 at 920 Hz, while in 4U 1608-52 we do not have data above 800 Hz. We discuss our results in the context of scenarios in which the soft lags are either due to reflection off the accretion disc or up-/down-scattering in a hot medium close to the neutron star. We finally explore the connection between, on one hand the time lags and the intrinsic coherence of the kHz QPOs, and on the other the QPOs' amplitude and quality factor in these two sources.

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