45 research outputs found
The NuSTAR View of a QPO Evolution of GRS 1915+105
We report a timing analysis of the black hole binary GRS 1915+105 with the
NuSTAR observatory. A strong type-C QPO below 2 Hz appears in the power density
spectrum during the whole observation, whose frequency is correlated with the
3-25 keV count rate. The QPO shows a sudden increase in frequency along with an
increase in flux and a softening of the spectrum. We discuss the possible
origin of the QPO and the reasons that lead to the QPO frequency variation. It
is suggested that the reflection component has little influence on QPO
frequency and the increase in QPO frequency could be associated with the inward
motion of the outer part of the disk.Comment: 21 pages, 8 figures, published in A
The accretion rate independence of horizontal branch oscillation in XTE J1701-462
We study the temporal and energy spectral properties of the unique neutron
star low-mass X-ray binary XTE J1701-462. After assuming the HB/NB vertex as a
reference position of accretion rate, the horizontal branch oscillation (HBO)
of the HB/NB vertex is roughly 50 Hz. It indicates that the HBO is independent
with the accretion rate or the source intensity. The spectral analysis shows
in the HB/NB vertex and
in the NB/FB vertex, which
implies that different accretion rate may be produced in the HB/NB vertex and
the NB/FB vertex. The Comptonization component could be fitted by constrained
broken power law (CBPL) or nthComp. Different with GX 17+2, the frequencies of
HBO positively correlate with the inner disk radius, which contradict with the
prediction of Lense-Thirring precession model. XTE J1701-462, both in the
Cyg-like phase and in the Sco-like phase, follows a positive correlation
between the break frequency of broad band noise and the characteristic
frequency of HBO, which is called the W-K relation. An anticorrelation between
the frequency of HBO and photon energy is observed. Moreover, the rms of HBO
increases with photon energy till ~10 keV. We discuss the possible origin of
HBO from corona in XTE J1701-462.Comment: 45 pages, 18 figures, accepted by Ap
Low Frequency Quasi-periodic Oscillations in the High-eccentric LMXB Cir X-1: Extending the WK Correlation for Z Sources
Using archival Rossi X-ray Timing Explorer (RXTE) data, we studied the low-frequency quasi-periodic oscillations (LFQPOs) in the neutron star low-mass X-ray binary (LMXB) Cir X-1 and examined their contribution to frequency-frequency correlations for Z sources. We also studied the orbital phase effects on the LFQPO properties and found them to be phase independent. Comparing LFQPO frequencies in different classes of LMXBs, we found that systems that show both Z and atoll states form a common track with atoll/BH sources in the so-called WK correlation, while persistent Z systems are offset by a factor of about two. We found that neither source luminosity nor mass accretion rate is related to the shift of persistent Z systems. We discuss the possibility of a misidentification of fundamental frequency for horizontal branch oscillations from persistent Z systems and interpreted the oscillations in terms of models based on relativistic precession
Reflare in MAXI J1348-630]{Evolution of disc and corona in MAXI J1348-630 during the 2019 reflare: NICER and Insight-HXMT view
In this work, using \textit{NICER} and \textit{Insight}-HXMT observations, we
present a study of the broadband spectral and timing evolution of the source
throughout the first reflare, which occurred about 4 months after the major
outburst. Our findings suggest that during the reflare, below a critical
luminosity (D/2.2 kpc) erg s,
the scale of the corona shrinks in the radial direction, whereas the inner
radius of the disk does not change considerably; however, the inner radius of
the disk starts to move inward when the source exceeds the critical luminosity.
We conclude that at low luminosity the increase in accretion rate only heats up
the inner zone of the accretion disc without the transfer of angular momentum
which occurs above a certain luminosity
The mHz quasi-regular modulations of 4U 1630--47 during its 1998 outburst
We present the results of a detailed timing and spectral analysis of the
quasi-regular modulation (QRM) phenomenon in the black hole X-ray binary 4U
1630--47 during its 1998 outburst observed by Rossi X-ray Timing Explore
(RXTE). We find that the 50-110 mHz QRM is flux dependent, and the QRM
is detected with simultaneous low frequency quasi-periodic oscillations
(LFQPOs). According to the behavior of the power density spectrum, we divide
the observations into four groups. In the first group, namely behavior A,
LFQPOs are detected, but no mHz QRM. The second group, namely behavior B, a QRM
with frequency above 88 mHz is detected and the 5 Hz and 7
Hz LFQPOs are almost overlapping. In the third group, namely behavior C, the
QRM frequency below 88 mHz is detected and the LFQPOs are significantly
separated. In the forth group, namely behavior D, neither QRM nor LFQPOs are
detected. We study the energy-dependence of the fractional rms, centroid
frequency, and phase-lag of QRM and LFQPOs for behavior B and C. We then study
the evolution of QRM and find that the frequency of QRM increases with
hardness, while its rms decreases with hardness. We also analyze the spectra of
each observation, and find that the QRM rms of behavior B has a positive
correlation with / . Finally, we give
our understanding for this mHz QRM phenomena.Comment: 14pages, 15 figure
High energy Millihertz quasi-periodic oscillations in 1A 0535+262 with Insight-HXMT challenge current models
We studied the millihertz quasi-periodic oscillation (mHz QPO) in the 2020
outburst of the Be/X-ray binary 1A 0535+262 using Insight-HXMT data over a
broad energy band. The mHz QPO is detected in the 27-120 keV energy band. The
QPO centroid frequency is correlated with the source flux, and evolves in the
35-95 mHz range during the outburst. The QPO is most significant in the 50-65
keV band, with a significance of ~ 8 sigma, but is hardly detectable (<2 sigma)
in the lowest (1-27 keV) and highest (>120 keV) energy bands. Notably, the
detection of mHz QPO above 80 keV is the highest energy at which mHz QPOs have
been detected so far. The fractional rms of the mHz QPO first increases and
then decreases with energy, reaching the maximum amplitude at 50-65 keV. In
addition, at the peak of the outburst, the mHz QPO shows a double-peak
structure, with the difference between the two peaks being constant at ~0.02
Hz, twice the spin frequency of the neutron star in this system. We discuss
different scenarios explaining the generation of the mHz QPO, including the
beat frequency model, the Keplerian frequency model, the model of two jets in
opposite directions, and the precession of the neutron star, but find that none
of them can explain the origin of the QPO well. We conclude that the
variability of non-thermal radiation may account for the mHz QPO, but further
theoretical studies are needed to reveal the physical mechanism.Comment: 13 pages, 7 figures. Accepted for publication in MNRA