L. M. Song

The correlations between the twin kHz quasi-periodic oscillation frequencies of low-mass X-ray binaries

We analyzed the recently published kHz QPO data in the neutron star low-mass X-ray binaries (LMXBs), in order to investigate the different correlations of the twin peak kilohertz quasi-eriodic oscillations (kHz QPOs) in bright Z sources and in the less luminous Atoll sources. We find that a power-law relation

The magnetic field evolution of ULX NuSTAR J095551+6940.8 in M82 – a legacy of accreting magnetar

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Investigation of the emission radii of kHz QPOs for the accreting millisecond X-Ray pulsars, Atoll and Z sources

between the upper and the lower kHz QPOs with different indices:

Morphological analysis on the coherence of kHz QPOs

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Time Lags of Z Source GX 5-1

1.5 for the Atoll source 4U 1728-34 and n

The rms-flux relations in different branches in Cyg X-2

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The minimum magnetic field of millisecond pulsars calculated according to accretion: application to the X-ray neutron star SAX J1808.4–3658 in a low-mass X-ray binary

1.9 for the Z source Sco X-1. The implications of our results for the theoretical models for kHz QPOs are discussed.

The Prompt Ultraviolet/Soft X-Ray Emission of GRBs

Ultraluminous X-ray sources are usually believed to be black holes with mass about 102-3M(circle dot). However, the recent discovery of NuSTAR J095551+ 6940.8 in M82 by Bachetti et al. shows that it holds the spin period P = 1.37 s and period derivative. P approximate to -2 x 10(-10) s s(-1), which provides a strong evidence that some ultraluminous X-ray sources could be neutron stars. We obtain that the source may be an evolved magnetar according to our simulation by employing the model of accretion induced the polar magnetic field decay and standard spin-up torque of an accreting neutron star. The results show that NuSTAR J095551+ 6940.8 is still in the spin-up process, and the polar magnetic field decays to about 4.5 x 10(12) Gafter accreting similar to 10(-2.5) M-circle dot, while the strong magnetic field exists in the out-polar region, which could be responsible for the observed low field magnetar. The ultra luminosity of the source can be explained by the beaming effect and two kinds of accretion-radial random accretion and disc accretion. Since the birth rate of magnetars is about ten per cent of the normal neutron stars, we guess that several ultraluminous X-ray sources should share the similar properties to that of NuSTAR J095551+6940.8.

X-ray afterglows of gamma-ray bursts in the synchrotron self-Compton dominated regime

We infer the emission positions of twin kilohertz quasi-periodic oscillations (kHz QPOs) in neutron star low mass X-ray binaries (NS-LMXBs) based on the Alfven wave oscillation model (AWOM). For most sources, the emission radii of kHz QPOs cluster around a region of 16-19 km with the assumed NS radii of 15 km. Cir X-1 has the larger emission radii of 23-38 km than those of the other sources, which may be ascribed to its large magnetosphere-disk radius or strong NS surface magnetic field. SAX J1808.4-3658 is also a particular source with the relative large emission radii of kHz QPOs of 20 - 23 km, which may be due to its large inferred NS radius of 18 - 19 km. The emission radii of kHz QPOs for all the sources are larger than the NS radii, and the possible explanations of which are presented. The similarity of the emission radii of kHz QPOs (16-19 km) for both the low/high luminosity Atoll/Z sources is found, which indicates that both sources share the similar magnetosphere- disk radii.

The energy dependence of the centroid frequency of the low-frequency quasi-periodic oscillations in XTE J1550–564

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)xa0The 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)xa0The 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 750xa0Hz. 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)xa0There 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.