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1.
By analyzing all archival Rossi X-ray timing explorer (RXTE) data of the neutron star low mass X-ray binary 4U1820-303, we investigate the detectability of simultaneous twin kHz quasi-periodic oscillations (QPOs) as a function of their frequency, width and root mean squared (RMS) amplitudes. In a blind search over the whole data set (spanning over about 10 years), we show that in continuous time intervals (2000–3000 s), twin QPOs are preferentially detected over narrow range of frequencies (100 Hz wide), leading to a clustering in the distribution of frequency ratios, and a gap around the point (600, 900) Hz in the correlation line that links the upper QPO frequency to the lower QPO frequency. A deficit of lower QPOs around 600 Hz had already been noticed by Belloni et al. [Belloni, T., Méndez, M., Homan, J., 2005. A&A 437, 209], it is now confirmed using a much larger data set. We show that the lack of twin QPOs within the gap is not due to a lack of sensitivity for QPO detection, if the parameters of the QPOs (RMS and width) can be interpolated within the gap, using values measured before and after. Since as previously noticed, the gap cannot be attributed to an incomplete sampling of the source states, it thus implies a sudden change of the QPO properties within the gap, either a loss of coherence or an amplitude decrease, or alternatively, that there may be forbidden frequencies in this system.  相似文献   

2.
The observations of the black hole binary Cygnus X-l were made in the energy band of 20–100keV with a balloon-borne Xenon-filled multiwire proportional counter telescope on 5th April 1992. Timing analysis of the data revealed the presence of Quasi-Periodic Oscillations (QPO) in the hard X-ray emission from the source. The QPO feature in the power density spectrum is broad with a peak at a frequency of 0.06 Hz. This result is compared with similar reports of QPOs in Cyg X-l in soft and hard X-rays. Short time scale random intensity variations in the X-ray light curve are described with a shot noise model.  相似文献   

3.
We present a detailed study of the X-ray energy and power spectral properties of the neutron star transient IGR J17191−2821. We discovered four instances of pairs of simultaneous kilohertz quasi-periodic oscillations (kHz QPOs). The frequency difference between these kHz QPOs is between 315 and 362 Hz. We also report on the detection of five thermonuclear type I X-ray bursts and the discovery of burst oscillations at ∼294 Hz during three of them. Finally, we report on a faint and short outburst precursor, which occurred about two months before the main outburst. Our results on the broad-band spectral and variability properties allow us to firmly establish the atoll source nature of IGR J17191−2821.  相似文献   

4.
We have investigated the Quasi Periodic Oscillation (QPO) properties of the transient accreting X-ray pulsar XTE J1858 + 034 during the second outburst of this source in April–May 2004. We have used observations made with the Proportional Counter Array (PCA) of the Rossi X-ray Timing Explorer (RXTE) during May 14–18, 2004, in the declining phase of the outburst. We detected the presence of low frequency QPOs in the frequency range of 140–185 mHz in all the RXTE-PCA observations. We report evolution of the QPO parameters with the time, X-ray flux, and X-ray photon energy. Though a correlation between the QPO centroid frequency and the instantaneous X-ray flux is not very clear from the data, we point out that the QPO frequency and the one day averaged X-ray flux decreased with time during these observations. We have obtained a clear energy dependence of the RMS variation in the QPOs, increasing from about 3% at 3 keV to 6% at 25 keV. The X-ray pulse profile is a single peaked sinusoidal, with pulse fraction increasing from 20% at 3 keV to 45% at 30keV. We found that, similar to the previous outburst, the energy spectrum is well fitted with a model consisting of a cut-off power law along with an iron emission line.  相似文献   

5.
We take the recently published data of twin kHz quasi-period oscillations (QPOs) in neutron star (NS) low-mass X-ray binaries (LMXBs) as the samples, and investigate the morphology of the samples, which focuses on the quality factor, peak frequency of kHz QPOs, and try to infer their physical mechanism. We notice that: (1) The quality factors of upper kHz QPOs are low (2～20 in general) and increase with the kHz QPO peak frequencies for both Z and Atoll sources. (2) The distribution of quality factor versus frequency for the lower kHz QPOs are quite different between Z and Atoll sources. For most Z source samples, the quality factors of lower kHz QPOs are low (usually lower than 15) and rise steadily with the peak frequencies except for Sco X-1, which drop abruptly at the frequency of about 750 Hz. While for most Atoll sources, the quality factors of lower kHz QPOs are very high (from 2 to 200) and usually have a rising part, a maximum and an abrupt drop. (3) There are three Atoll sources (4U 1728-34, 4U 1636-53 and 4U 1608-52) of displaying very high quality factors for lower kHz QPOs. These three sources have been detected with the spin frequencies and sidebands, in which the source with higher spin frequency presents higher quality factor of lower kHz QPOs and lower difference between sideband frequency and lower kHz QPO frequency.  相似文献   

6.
Modern methods of spectral estimation based on parametric time-series models are useful tools in power spectral analysis. We apply the autoregressive (AR) model to study quasi-periodic oscillations (QPOs). An empirical formula to estimate the expectation and standard deviation of the noise AR power densities is derived, which can be used to estimate the statistical significance of an apparent QPO peak in an AR spectrum. An iterative adding-noise algorithm in AR spectral analysis is proposed and applied to studying QPOs in the X-ray binary Cir X-1.  相似文献   

7.
We report the results of a systematic timing analysis of RXTE observations of GRS 1915+105 when the source was in its variability class θ, characterized by alternating soft and hard states on a time-scale of a few hundred seconds. The aim was to examine the high-frequency part of the power spectrum in order to confirm the hectohertz quasi-periodic oscillations (QPO) previously reported from observations from mixed variability behaviours. During the hard intervals (corresponding to state C in the classification of Belloni et al.), we find a significant QPO at a frequency of ∼170 Hz, although much broader (Q∼2) than previously reported. No other significant peak is observed at frequencies >30 Hz. A time-resolved spectral analysis of selected observations shows that the hard intervals from class θ show a stronger and steeper  (Γ= 2.8–3.0)  power-law component than hard intervals from other classes. We discuss these results in the framework of hectohertz QPOs reported from GRS 1915+105 and other black hole binaries.  相似文献   

8.
利用“慧眼”(Hard X-ray Modulation Telescope, Insight-HXMT)卫星在2017年9月对黑洞候选体MAXI J1535-571的观测数据,研究了该源在爆发期内的时变现象.当源处于不同的爆发谱态时,功率密度谱的谱型存在明显差异.在硬中间态,有明显的限带噪声(band-limited noise)成分和QPO (Quasi-Periodic Oscillation)成分.分析结果表明:低频限带噪声的特征频率随能量的变化呈现正相关,即软能段光子的特征频率小于硬能段光子的特征频率. 0.1–0.5 Hz频率区间的限带噪声RMS (Root Mean Square)谱在硬中间态和软中间态均出现峰值,且在高能端存在差异,可能是主导噪声RMS的能谱成分占比不同.当谱态由硬中间态过渡到软中间态时, C型QPO的RMS谱保持相似趋势,但限带噪声RMS谱存在谱态依赖现象,暗示着噪声和QPO有不同的起源机制.  相似文献   

9.
We propose three mechanisms for the generation of quasi-periodic oscillations (QPOs) in X-ray binaries. Two of them are based on an analogy with nonlinear oscillations of gaseous cavities in a fluid. The first mechanism, called magnetocavitation, implies that X-ray QPOs are produced by radial oscillations of the neutron-star magnetosphere interacting with accreted plasma. The photon-cavitation mechanism is considered when studying X-ray QPOs in neutron stars with critical (Eddington) luminosities. In this case, X-ray QPOs are generated by radial oscillations of photon cavities in the fully ionized hydrogen plasma that settles in the accretion column of a compact object. The mechanism according to which X-ray QPOs result from nonlinear oscillations of current sheets originating in accretion disks is suggested to explain QPOs in X-ray binaries with black holes and in cataclysmic variables. The calculated values of basic physical parameters of QPOs, such as the characteristic frequency, the dependences of QPO frequency and amplitude on X-ray flux, photon energy, and QPO lag time between photons at different energies are in good agreement with observational data.  相似文献   

10.
Using the recently published data of twin kHz quasi‐period oscillations (QPOs) in neutron stars of low‐mass X‐ray binaries (LMXBs), we study the different profiles between bright Z sources and less luminous Atoll sources. The quality factors of upper kHz QPOs show a narrow distribution both for Z sources and Atoll sources, which concentrate at 7.98 and 9.75, respectively. The quality factors of lower kHz QPOs show a narrow distribution for Z sources and a broader distribution for Atoll sources, which concentrate at 5.25 and 86.22, respectively. In order to investigate the relation between the quality factor and the peak frequency of kHz QPOs, we fit the data with power‐law, linear, and exponential functions, respectively. There is an obvious trend that the quality factors increase with the peak frequencies both for upper and lower QPOs. The implications of our results are discussed (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

11.
We have produced the colour–colour diagram of all the observations of 4U 1728–34 available in the Rossi X-ray Timing Explorer public archive (from 1996 to 2002) and found observations filling in a previously reported 'gap' between the island and the banana X-ray states. We have made timing analysis of these gap observations and found, in one observation, two simultaneous kHz quasi-periodic oscillations (QPOs). The timing parameters of these kHz QPOs fit in the overall trend of the source. The 'lower' kHz QPO has a centroid frequency of ∼308 Hz. This is the lowest 'lower' kHz QPO frequency ever observed in 4U 1728–34. The peak frequency separation between the 'upper' and the 'lower' kHz QPO is  Δν= 274 ± 11 Hz  , significantly smaller than the constant value of  Δν∼ 350 Hz  found when the 'lower' kHz QPO frequency is between ∼500 and 800 Hz. This is the first indication in this source for a significant decrease of kHz QPO peak separation towards low frequencies. We compare the result briefly to theoretical models for kHz QPO production.  相似文献   

12.
Among the variability behaviours exhibited by neutron star systems are the so-called 'horizontal branch oscillations' (HBO, with frequencies ≈50 Hz), the 'lower-frequency kHz quasi-periodic oscillation' (QPO) and the 'upper-frequency kHz QPO', with the latter two features being separated in frequency by an amount comparable to, but varying slightly from, the suspected spin-frequency of the neutron star. Recently, Psaltis, Belloni & van der Klis have suggested that there exists a correlation between these three frequencies that, when certain identifications of variability features are made, even encompasses black hole sources. We consider this hypothesis by reanalysing a set of GX 339−4 observations. The power spectral density (PSD) constructed from a composite of seven separate, but very similar, observations shows evidence for three broad peaks in the PSD. If the peak frequencies of these features are identified with QPO, then their frequencies approximately fit the correlations suggested by Psaltis, Belloni, & van der Klis. We also reanalyse a Cyg X-1 observation and show that the suggested QPO correlation may also hold, but that complications arise when the QPOs (which, in reality, are fairly broad features) are considered as a function of energy band. These fits suggest the existence of at least three separate, independent physical processes in the accretion flow, a hypothesis that is also supported by consideration of the Fourier frequency-dependent time lags and coherence function between variability in different energy bands. If these variability features have a common origin in neutron star and black hole systems, then 'beat frequency models' of kHz QPO in neutron star systems are called into question.  相似文献   

13.
In this paper we report on further observations of the third and fourth kilohertz quasi-periodic oscillations (QPOs) in the power spectrum of the low-mass X-ray binary (LMXB) 4U 1636−53. These kilohertz QPOs are sidebands to the lower kilohertz QPO. The upper sideband has a frequency  55.5 ± 1.7 Hz  larger than that of the contemporaneously measured lower kilohertz QPO. Such a sideband has now been measured at a significance  >6σ  in the power spectra of three neutron-star LMXBs (4U 1636−53, 1728−34 and 1608−52). We also confirm the presence of a sideband at a frequency ∼55 Hz less than the frequency of the lower kilohertz QPO. The lower sideband is detected at a 3.5σ level only when the lower kilohertz QPO frequency is between 800 and 850 Hz. In that frequency interval, the sidebands are consistent with being symmetric around the lower kilohertz QPO frequency. The upper limit to the rms amplitude of the lower sideband is significantly lower than that of the upper sideband for lower kilohertz QPO frequencies >850 Hz. Symmetric sidebands are unique to 4U 1636−53. This might be explained by the fact that lower kilohertz QPO frequencies as high as 800–850 Hz are rare for 4U 1728−34 and 1608−52. Finally, we also measured a low-frequency QPO at a frequency of ∼43 Hz when the lower kilohertz QPO frequency is between 700 and 850 Hz. A similar low-frequency QPO is present in the power spectra of the other two systems for which a sideband has been observed. We briefly discuss the possibility that the sideband is caused by Lense–Thirring precession.  相似文献   

14.
Low and intermediate frequency quasi-periodic oscillations (QPOs) are thought to be due to oscillations of Comptonizing regions or hot regions embedded in Keplerian discs. Observational evidence of evolutions of QPOs would therefore be very important as they throw lights on the dynamics of the hotter region. Our aim is to find systems in which there is a well-defined correlation among the frequencies of the QPOs over a range of time so as to understand the physical picture. In this paper, we concentrate on the archival data of XTE J1550−564 obtained during 1998 outburst, and study the systematic drifts during the rising phase from the 1998 September 7 to the 1998 September 19, when the QPO frequency increased monotonically from 81 mHz to 13.1 Hz. Immediately after that, QPO frequency started to decrease and on the 1998 September 26, the QPO frequency became 2.62 Hz. After that, its value remained almost constant. This frequency drift can be modelled satisfactorily with a propagatory oscillating shock solution where the post-shock region behaves as the Comptonized region. Comparing with the nature of a more recent 2005 outburst of another black hole candidate GRO 1655−40, where QPOs disappeared at the end of the rising phase, we conjecture that this so-called 'outburst' may not be a full-fledged outburst.  相似文献   

15.
There are remarkable similarities between the rapid X-ray variability of low-magnetic field neutron stars in low mass X-ray binaries, and that of black holes. In particular at frequencies < 100 Hz, their power spectra can be strikingly similar. The highest frequency phenomena (kilohertz QPOs, black hole high-frequency QPOs and neutron star hectohertz QPOs) are the ones that show most differences, perhaps because they originate closest to the compact object. Most variability components vary in frequency in correlation with one another, and the correlations once again are very similar across neutron stars and black holes – some extend even to white dwarfs. Although this does not strictly require that all phenomena whose frequencies are involved are caused by the same physics in all three source types, this does indicate that basic properties of the accretion flow which are the same in all three source types play an important role in generating at least some of the frequencies.  相似文献   

16.
On 27th December 2004 SGR 1806–20, one of the most active Soft γ-ray Repeaters (SGRs), displayed an extremely rare event, also known as giant flare, during which up to 1047 ergs were released in the ∼1–1000 keV range in less than 1 s. Before and after the giant flare we carried out IR observations by using adaptive optics (NAOS-CONICA) mounted on VLT which provided images of unprecedented quality (FWHM better than 0.1″). We discovered the likely IR counterpart to SGR 1806–20 based on positional coincidence with the VLA uncertainty region and flux variability of a factor of about 2 correlated with that at higher energies. Moreover, by analysing the Rossi-XTE/PCA data we have discovered rapid Quasi-Periodic Oscillations (QPOs) in the pulsating tail of the 27th December 2004 giant flare of SGR 1806–20. QPOs at ∼92.5 Hz are detected in a 50 s interval starting 170 s after the onset of the giant flare. These QPOs appear to be associated with increased emission by a relatively hard unpulsed component and are seen only over phases of the 7.56 s spin period pulsations away from the main peak. QPOs at ∼18 and ∼30 Hz are also detected ∼200–300 s after the onset of the giant flare. This is the first time that QPOs are unambiguously detected in the flux of a Soft Gamma-ray Repeater, or any other isolated neutron star. We interpret the highest QPOs in terms of the coupling of toroidal seismic modes with Alfvén waves propagating along magnetospheric field lines. The lowest frequency QPO might instead provide indirect evidence on the strength of the internal magnetic field of the neutron star.   相似文献   

17.
利用线性状态空间模型（Ｌｉｎｅａｒ Ｓｔａｔｅ Ｓｐａｃｅ Ｍｏｄｅｌ－ＬＳＳＭ）,将 Ｃｙｇ Ｘ－１的功率谱分解为ＬＳＳＭ产生的模型功率谱和剩余功率谱两部分．集中分析剩余功率谱,结果显示, Ｃｙｇ Ｘ－１在低／硬态、转换态和高／软态三种状态的剩余功率谱有着不同的结构特征．其中高／软态和低／硬态的剩余功率谱存在一个宽峰结构,中心频率分别为～ ８ Ｈｚ和～ ５ Ｈｚ,低／硬态的剩余功率诺在～ ０．０７ Ｈｚ达到极大;转换态的剩余功率谱有双峰结构,其中心频率分别在～０．５—４Ｈｚ和～５—１１Ｈｚ,与我们以前分析的 ＱＰＯ的中心频率很接近,说明 ＱＰＯ与线性状态空间所要求的自回归模型可能属于不同的物理过程．与总功率谱比较,剩余功率谱对谱的变化部分（例如ＱＰＯ、截断频率等）更为敏感,本文对剩余功率谱中谱峰变化的原因做了初步的探讨．  相似文献   

18.
Using the data observed by Rossi X-ray Timing Explorer, a systematic study of temporal phenomena of the black-hole transient XTE J1650-500 in its 2001–2002 outburst is presented. By using the time lag in the Fourier frequency domain, three characteristic frequency ranges are analysed, namely the band limited noise, red noise, and QPOs (Quasi-Periodic Oscillations). The properties and evolution behaviours in these frequency ranges may be dominated by different accretion regions. It is commonly believed that the smaller timescale corresponds to the more inner region. The low-hard state and hard intermediate state are especially highlighted. The results of data analysis are discussed in the framework of Lense-Thirring precession. Results are in favor of the disturbance propagation model for explaining the observed time lags. Although the timing analysis in the frequency ranges of band-limited noise and red noise is carried out, and a possibly existed inflection point is found, the model to explain them is still not well established. More work is needed to understand the innermost accretion region.  相似文献   

19.
We report results from a spectral and timing analysis of M82 X-1, one of the brightest known ultraluminous X-ray sources. Data from a new 105-ks XMM–Newton observation of M82 X-1, performed in 2004 April, and of archival RossiXTE observations are presented. A very soft thermal component is present in the XMM spectrum. Although it is not possible to rule out a residual contamination from the host galaxy, modelling it with a standard accretion disc would imply a black hole (BH) mass of  ≈103 M⊙  . An emission line was also detected at an energy typical for fluorescent Fe emission. The power density spectrum of the XMM observation shows a variable Quasi-Periodic Oscillation (QPO) at frequency of 113 mHz with properties similar to those discovered by Strohmayer and Mushotzky. The QPO was also found in seven archival RXTE observations, that include those analysed by Strohmayer and Mushotzky, and Fiorito and Titarchuk. A comparison of the properties of this QPO with those of the various types of QPOs observed in Galactic black hole candidates strongly suggests an association with the type-C, low-frequency QPOs. Scaling the frequency inversely to the BH mass, the observed QPO frequency range (from 50 to 166 mHz) would yield a BH mass anywhere in the interval few tens to  1000  M⊙  .  相似文献   

20.
A model for the high-frequency (20–2400 Hz) quasi-periodic oscillations (QPOs) of magnetars based on the representation of coronal magnetic loops as equivalent electric RLC circuits is proposed. The observed periods of the QPOs and their high Q-factor (Q ≈ 104–105) are explained. It follows from the model that the QPOs can be excited not only in the tail of a flare but also before the main pulse. The parameters of the QPO source at the “ringing tail” stage of the flare from SGR 1806–20 on December 27, 2004, have been estimated: electric current I ≈ 3 × 1019 A, minimum magnetic field strength B min ≈ 1013 G, and electron density n ≈ 2 × 1016 cm−3.  相似文献   

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