scholarly journals A systematic analysis of the phase lags associated with the type-C quasi-periodic oscillation in GRS 1915+105

2020 ◽  
Vol 494 (1) ◽  
pp. 1375-1386 ◽  
Author(s):  
Liang Zhang ◽  
Mariano Méndez ◽  
Diego Altamirano ◽  
Jinlu Qu ◽  
Li Chen ◽  
...  
Keyword(s):  
Second Harmonic ◽  
Periodic Oscillation ◽  
Energy Spectra ◽  
Phase Lag ◽  
Physical Origin ◽  
Systematic Analysis ◽  
Quasi Periodic Oscillation ◽  
Phase Lags ◽  
Type C ◽  
Subharmonic Frequency

ABSTRACT We present a systematic analysis of the phase lags associated with the type-C quasi-periodic oscillations (QPOs) in GRS 1915+105 using RXTE data. Our sample comprises 620 RXTE observations with type-C QPOs ranging from ∼0.4 to ∼6.3 Hz. Based on our analysis, we confirm that the QPO phase lags decrease with QPO frequency, and change sign from positive to negative at a QPO frequency of ∼2 Hz. In addition, we find that the slope of this relation is significantly different between QPOs below and above 2 Hz. The relation between the QPO lags and QPO rms can be well fitted with a broken line: as the QPO lags go from negative to positive, the QPO rms first increases, reaching its maximum at around zero lag, and then decreases. The phase-lag behaviour of the subharmonic of the QPO is similar to that of the QPO fundamental, where the subharmonic lags decrease with subharmonic frequency and change sign from positive to negative at a subharmonic frequency of ∼1 Hz; on the contrary, the second harmonic of the QPO shows a quite different phase-lag behaviour, where all the second harmonics show hard lags that remain more or less constant. For both the QPO and its (sub)harmonics, the slope of the lag–energy spectra shows a similar evolution with frequency as the average phase lags. This suggests that the lag–energy spectra drive the average phase lags. We discuss the possibility for the change in lag sign, and the physical origin of the QPO lags.

scholarly journals The Evolution of the Phase Lags Associated with the Type-C Quasi-periodic Oscillation in GX 339–4 during the 2006/2007 Outburst

2017 ◽  
Vol 845 (2) ◽  
pp. 143 ◽  
Author(s):  
Liang Zhang ◽  
Yanan Wang ◽  
Mariano Méndez ◽  
Li Chen ◽  
Jinlu Qu ◽  
...  
Keyword(s):  
Periodic Oscillation ◽  
Quasi Periodic Oscillation ◽  
Phase Lags ◽  
Type C

scholarly journals Time lags of the type-B quasi-periodic oscillation in MAXI J1348−630

2020 ◽  
Vol 496 (4) ◽  
pp. 4366-4371 ◽  
Author(s):  
Tomaso M Belloni ◽  
Liang Zhang ◽  
Nikolaos D Kylafis ◽  
Pablo Reig ◽  
Diego Altamirano
Keyword(s):  
Periodic Oscillation ◽  
High Signal ◽  
Time Lags ◽  
Type B ◽  
Quasi Periodic Oscillation ◽  
Black Hole Binaries ◽  
Relativistic Jet ◽  
Noise Data ◽  
Phase Lags ◽  
First Time

ABSTRACT The fast variability observed in the X-ray emission from black hole binaries has a very complex phenomenology, but offers the possibility to investigate directly the properties of the inner accretion flow. In particular, type-B oscillations in the 2–8 Hz range, observed in the soft-intermediate state, have been associated with the emission from a relativistic jet. We present the results of the timing and spectral analysis of a set of observations of the bright transient MAXI J1348−630 made with the NICER (Neutron Star Interior Composition Explorer) telescope. The observations are in the brightest part of the outburst and all feature a strong type-B quasi-periodic oscillation (QPO) at ∼4.5 Hz. We compute the energy dependence of the fractional rms and the phase lags at the QPO frequency, obtaining high signal-to-noise data and sampling for the first time at energies below 2 keV. The fractional rms decreases from more than 10 per cent at 9 keV to 0.6 per cent at 1.5 keV, and is constant below that energy. Taking the 2–3 keV band as reference, photons at all energies show a hard lag, increasing with the distance from the reference band. The behaviour below 2 keV has never been observed before, due to the higher energy bandpass of previous timing instruments. The energy spectrum can be fitted with a standard model for this state, consisting of a thin disc component and a harder power law, plus an emission line between 6 and 7 keV. We discuss the results, concentrating on the phase lags, and show that they can be interpreted within a Comptonization model.

scholarly journals A variable-frequency HFQPO in GRS 1915+105 as observed with AstroSat

2019 ◽  
Vol 489 (1) ◽  
pp. 1037-1043 ◽  
Author(s):  
Tomaso M Belloni ◽  
Dipankar Bhattacharya ◽  
Pietro Caccese ◽  
Varun Bhalerao ◽  
Santosh Vadawale ◽  
...  
Keyword(s):  
Periodic Oscillation ◽  
Large Area ◽  
Quasi Periodic Oscillation ◽  
X Ray ◽  
Phase Lags ◽  
Time Variations ◽  
Area X ◽  
First Time ◽  
Observation Period

ABSTRACT From the analysis of more than 92 ks of data obtained with the Large Area X-Ray Proportional Counter (LAXPC) instrument onboard AstroSat we have detected a clear high-frequency quasi-periodic oscillation (HFQPO) whose frequency varies between 67.4 and 72.3 Hz. In the classification of variability classes of GRS 1915+105, at the start of the observation period the source was in class ω and at the end the variability was that of class μ: both classes are characterized by the absence of hard intervals and correspond to disc-dominated spectra. After normalization to take into account time variations of the spectral properties as measured by X-ray hardness, the QPO centroid frequency is observed to vary along the hardness–intensity diagram, increasing with hardness. We also measure phase lags that indicate that HFQPO variability at high energies lags that at lower energies and detect systematic variations with the position on the hardness–intensity diagram. This is the first time that (small) variations of the HFQPO frequency and lags are observed to correlate with other properties of the source. We discuss the results in the framework of existing models, although the small (7 per cent) variability observed is too small to draw firm conclusions.

scholarly journals Re-observing the NLS1 galaxy RE J1034+396 – II. New insights on the soft X-ray excess, QPO, and the analogy with GRS 1915+105

2020 ◽  
Vol 500 (2) ◽  
pp. 2475-2495
Author(s):  
Chichuan Jin ◽  
Chris Done ◽  
Martin Ward
Keyword(s):  
Active Galactic Nucleus ◽  
Vertical Structure ◽  
Accretion Rate ◽  
Timing Analysis ◽  
Periodic Oscillation ◽  
Phase Lag ◽  
Quasi Periodic Oscillation ◽  
X Ray ◽  
Hot Corona ◽  
Physical Analogy

ABSTRACT The active galactic nucleus (AGN) RE J1034+396 displays the most significant X-ray quasi-periodic oscillation (QPO) detected so far. We perform a detailed spectral-timing analysis of our recent simultaneous XMM–Newton, NuSTAR, and Swift observations. We present the energy dependence of the QPO’s frequency, rms, coherence, and phase lag, and model them together with the time-averaged spectra. Our study shows that four components are required to fit all the spectra. These components include an inner disc component (diskbb), two warm corona components (CompTT-1 and CompTT-2), and a hot corona component (nthComp). We find that diskbb, CompTT-2 (the hotter but less luminous component), and nthComp all contain the QPO signal, while CompTT-1 only exhibits stochastic variability. By fitting the lag spectrum, we find that the QPO in diskbb leads CompTT-2 by 679 s, and CompTT-2 leads nthComp by 180 s. By only varying the normalizations, these components can also produce good fits to the time-averaged and variability spectra obtained from previous observations when QPOs were present and absent. Our multiwavelength study shows that the detectability of the QPO does not depend on the contemporaneous mass accretion rate. We do not detect a significant Iron K α emission line, or any significant reflection hump. Finally, we show that the rms and lag spectra in the latest observation are very similar to the 67-Hz QPO observed in the micro-quasar GRS 1915+105. These new results support the physical analogy between these two sources. We speculate that the QPO in both sources is due to the expansion/contraction of the vertical structure in the inner disc.

Rotor Wake Generated Unsteady Aerodynamic Response of a Compressor Stator

1978 ◽  
Vol 100 (4) ◽  
pp. 664-675 ◽  
Author(s):  
S. Fleeter ◽  
R. L. Jay ◽  
W. A. Bennett
Keyword(s):  
Pressure Difference ◽  
Second Harmonic ◽  
Incidence Angle ◽  
Dynamic Pressure ◽  
Pressure Differential ◽  
Phase Lag ◽  
Trailing Edge ◽  
Unsteady Pressure ◽  
Forcing Function ◽  
Reduced Frequency

An experimental investigation was conducted to determine the fluctuating pressure distribution on a stationary vane row, with the primary source of excitation being the wakes from the upstream rotor blades. This was accomplished in a large scale, low speed, single stage research compressor. The forcing function, the velocity defect created by the rotor wakes, was measured with a crossed hot-wire probe. The aerodynamic response on the vanes was measured by means of flush mounted high response dynamic pressure transducers. The dynamic data were analyzed to determine the chordwise distribution of the dynamic pressure coefficient and aerodynamic phase lag as referenced to a transverse gust at the vane leading edge. Vane suction and pressure surface data as well as the pressure difference across the vane were obtained for reduced frequency values ranging from 3.65 to 16.80 and for an incidence angle range of 35.5 deg. The pressure difference data were correlated with a state-of-the-art aerodynamic cascade transverse gust analysis. The correlation was quite good for all reduced frequency values for small values of incidence. For the more negative incidence angle data points, it was shown that a convected wake phenomena not modeled in the analysis existed. Both the first and second harmonic unsteady pressure differential magnitude data decrease in the chordwise direction. The second harmonic magnitude data attains a value very nearly zero at the vane trailing edge transducer location, while the first harmonic data is still finite, albeit small, at this location. That the magnitude of the unsteady pressure differential data approaches zero near to the trailing edge, particularly the second harmonic data which has reduced frequency values to 16.8, is significant in that it reflects upon the validity of the Kutta condition for unsteady flows.

scholarly journals Stochastic modeling of kHz quasi-periodic oscillation light curves

2006 ◽  
Vol 452 (2) ◽  
pp. 383-386 ◽  
Author(s):  
R. Vio ◽  
P. Rebusco ◽  
P. Andreani ◽  
H. Madsen ◽  
R. V. Overgaard
Keyword(s):  
Stochastic Modeling ◽  
Periodic Oscillation ◽  
Light Curves ◽  
Quasi Periodic Oscillation
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