Types Of Quasi-periodic Oscillations Research Articles

The X-ray corona in the black hole binary GRO J1655−40 from the properties of non-harmonically related quasi-periodic oscillations

ABSTRACT The study of quasi-periodic oscillations (QPOs) plays a vital role in understanding the nature and geometry of the Comptonizing medium around black hole X-ray binaries. The spectral-state dependence of various types of QPOs (namely A, B, and C) suggests that they could have different origins. The simultaneous presence of different types of QPOs would therefore imply the simultaneous occurrence of different mechanisms. In this work, we study the radiative properties of two non-harmonically related QPOs in the black hole binary GRO J1655−40 detected at the peak of the ultraluminous state during the 2005 outburst of the source. The two QPOs have been previously identified as types B and C, respectively. We jointly fit the phase-lag and rms spectra of the QPOs and the time-averaged spectrum of the source with the time-dependent Comptonization model vkompth to infer the geometry of the media producing the QPOs. The time-averaged spectrum required a hot disc of 2.3 keV and a steep power law with index 2.7, revealing that the source was in an ultraluminous state. The corona that drives the variability of the type-B QPO is smaller in size and has a lower feedback fraction than the one that drives the variability of the type-C QPO. This suggests the simultaneous presence of a horizontally extended corona covering the accretion disc and a vertically elongated jet-like corona that are responsible for the type-C and B QPOs, respectively.

A journey from the hard to the soft state: How do QPOs evolve in the 2021 outburst of GX 339–4?

ABSTRACT We investigated the snapshots of five NICER observations of the black hole transient GX 339–4 when the source transited from the hard state into the soft state during its outburst in 2021. In this paper, we focused our study on the evolution of quasi-periodic oscillations (QPOs) and noise components using power-density spectra. In addition, we derived hardness ratios by comparing count rates above and below 2 keV. The evolution from the hard to the soft state was a somewhat erratic process, showing several transitions between states that are dominated by top-flat noise and can show type-C QPOs; those that are dominated by red noise and can show type-B QPOs. From the parameters that we studied, we only found a strong correlation between the hardness ratio and the type of QPO observed. This implies that the appearance of type-B QPOs is related to a change in the accretion geometry of the system that also reflects in altered spectral properties. We also observed that the type-B QPO forms from or disintegrates into a broad peaked feature when the source comes out of or goes to the hard intermediate state, respectively. This implies some strong decoherence in the process that creates this feature.

Black hole mass and spin measurements through the relativistic precession model: XTE J1859+226

ABSTRACT The X-ray light curves of accreting black holes and neutron stars in binary systems show various types of quasi-periodic oscillations (QPOs), the origin of which is still debated. The relativistic precession model identifies the QPO frequencies with fundamental time-scales from General Relativity, and has been proposed as a possible explanation of certain types of such oscillations. Under specific conditions (i.e. the detection of a particular QPOs triplet) such a model can be used to obtain self-consistent measurements of the mass and spin of the compact object. So far this has been possible only in the black hole binary GRO J1655-40. In the RXTE/PCA data from the 1999–2000 outburst of the black hole transient XTE J1859+226 we found a QPO triplet, and used the relativistic precession model to obtain high-precision measurements of the black hole mass and spin – M = (7.85 ± 0.46) M⊙, a* = 0.149 ± 0.005 – the former being consistent with the most recent dynamical mass determination from optical measurements. Similarly to what has been already observed in other black hole systems, the frequencies of the QPOs and broad-band noise components match the general relativistic frequencies of particle motion close to the compact object predicted by the model. Our findings confirm previous results and further support the validity of the relativistic precession model, which is the only electromagnetic-measurement-based method that so far has consistently yielded spins close to those from the gravitational waves produced by merging binary black holes.

Transitions and Origin of the Type-B Quasi-periodic Oscillations in the Black Hole X-Ray Binary MAXI J1348–630

The fast transitions between different types of quasi-periodic oscillations (QPOs) are generally observed in black hole transient sources (BHTs). We present a detailed study of the timing and spectral properties of the transitions of type-B QPOs in MAXI J1348–630, observed by Insight-HXMT. The fractional rms variability–energy relationship and energy spectra reveal that type-B QPOs probably originate from jet precession. Compared to a weak power-law dominated power spectrum, when type-B QPOs are present, the corresponding energy spectrum shows an increase in the Comptonization component and the need for the xillverCp component, and a slight increase in the height of the corona when using the relxilllp model. Therefore, we suggest that a coupled inner disk-jet region is responsible for the observed type-B QPO transitions. The timescale for the appearance/disappearance of type-B QPOs is either long or short (seconds), which may indicate instability of the disk-jet structure. For these phenomena, we hypothesize that the Bardeen–Petterson effect causes the disk-jet structure to align with the BH spin axis or that the disappearance of small-scale jets bound by the magnetic flux tubes leads to the disappearance of type-B QPOs. We observed three events regarding the B/C transitions, one of which occurred over a short time period from ∼9.2 Hz (C) to ∼4.8 Hz (B). The energy spectral analysis for the other two transitions shows that when type-C QPO is present, the Comptonization flux is higher, the spectrum is harder, and the inner radius of the disk changes insignificantly. We suggest that type-C QPOs probably originate from relatively stronger jets or the corona.

A machine learning approach for classification of accretion states of black hole binaries

ABSTRACT In this paper, we employ Machine Learning algorithms on multimission observations for the classification of accretion states of outbursting black hole X-ray binaries for the first time. Archival data from RXTE, Swift, MAXI, and AstroSat observatories are used to generate the hardness intensity diagrams (HIDs) for outbursts of the sources XTE J1859+226 (1999 outburst), GX 339−4 (2002, 2004, 2007, and 2010 outbursts), IGR J17091−3624 (2016 outburst), and MAXI J1535−571 (2017 outburst). Based on variation of X-ray flux, hardness ratios, presence of various types of quasi-periodic oscillations (QPOs), photon indices, and disc temperature, we apply clustering algorithms like K-Means clustering and Hierarchical clustering to classify the accretion states (clusters) of each outburst. As multiple parameters are involved in the classification process, we show that clustering algorithms club together the observations of similar characteristics more efficiently than the ‘standard’ method of classification. We also infer that K-Means clustering provides more reliable results than Hierarchical clustering. We demonstrate the importance of the classification based on machine learning by comparing it with results from ‘standard’ classification.

Can Lense–Thirring Precession Produce QPOs in Supersonic Accretion Flows?

Abstract The timing properties of X-ray binaries are still not understood, particularly the presence of quasi-periodic oscillations (QPOs) in their X-ray power spectra. The solid-body regime of Lense–Thirring precession is one prominent model invoked to explain the most common type of QPOs, Type C. However, solid-body precession requires a specific structure that has not been examined in light of constrained properties of accretion flows. We assume in this paper, as solid-body precession requires, a disk separated into two flows at a transition radius r t : a cold outer flow and a hot inner flow (playing the role of the corona). We explore the physical structure of both flows using model-independent estimates of accretion parameters. We show that, in order to reproduce the observed X-ray spectra during luminous hard states, the hot flow must accrete at sonic to supersonic speeds, unreachable with typical viscous torques. As a result of this extreme accretion speed (or high α parameter), no region of the disk during these states lies in the “wave-like” regime required for solid-body precession. Furthermore, we expect the flow to align with the black hole spin axis via the Bardeen–Petterson effect inside a radius r break > r t . As a consequence, the hot inner flow cannot exhibit solid body precession—as currently pictured in the literature—during luminous hard states. Since Type C QPOs are prevalent in these states, we conclude that this mechanism is unlikely to be responsible for producing Type C QPOs around stellar mass black holes.

NICER observations reveal that the X-ray transient MAXI J1348−630 is a black hole X-ray binary

ABSTRACT We studied the outburst evolution and timing properties of the recently discovered X-ray transient MAXI J1348−630 as observed with NICER. We produced the fundamental diagrams commonly used to trace the spectral evolution, and power density spectra to study the fast X-ray variability. The main outburst evolution of MAXI J1348−630 is similar to that commonly observed in black hole transients. The source evolved from the hard state (HS), through hard- and soft-intermediate states, into the soft state in the outburst rise, and back to the HS in reverse during the outburst decay. At the end of the outburst, MAXI J1348−630 underwent two reflares with peak fluxes approximately one and two orders of magnitude fainter than the main outburst, respectively. During the reflares, the source remained in the HS only, without undergoing any state transitions, which is similar to the so-called ‘failed outbursts’. Different types of quasi-periodic oscillations (QPOs) are observed at different phases of the outburst. Based on our spectral-timing results, we conclude that MAXI J1348−630 is a black hole candidate.

A Rapid Change in X-Ray Variability and a Jet Ejection in the Black Hole Transient MAXI J1820+070

Abstract We present Neutron Star Interior Composition Explorer X-ray and Arcminute Microkelvin Imager Large Array radio observations of a rapid hard-to-soft state transition in the black hole X-ray transient MAXI J1820+070. During the transition from the hard state to the soft state a switch between two particular types of quasiperiodic oscillations (QPOs) was seen in the X-ray power density spectra, from type-C to type-B, along with a drop in the strength of the broadband X-ray variability and a brief flare in the 7–12 keV band. Soon after this switch (∼2–2.5 hr) a strong radio flare was observed that corresponded to the launch of superluminal ejecta. Although hints of a connection between QPO transitions and radio flares have been seen in other black hole X-ray transients, our observations constitute the strongest observational evidence to date for a link between the appearance of type-B QPOs and the launch of discrete jet ejections.

A Timing Study of MAXI J1820+070 Based on Swift/XRT and NICER Monitoring in 2018/19

Abstract We present a detailed timing analysis of the bright black hole X-ray binary MAXI J1820+070 (ASASSN-18ey), during its first detected outburst lasting from 2018 March until 2019 October based on Swift/XRT window timing mode observations, corresponding UVOT data and NICER observations. The light curves clearly show four outbursts, with the source remaining in the hard state during its first outburst, while the rise of the second outburst corresponds with the transition to the soft state. A similar double outburst of GX339-4 has been observed in 2004. Here it is followed by two hard-state only outbursts. In many observations the power density spectra showed type-C quasi-periodic oscillations (QPOs) with characteristic frequencies below 1 Hz, which suggests that the source stayed in a state of low effective accretion for large parts of its outburst. The absence of other types of QPOs hinders a precise determination of the state transitions, but from combining NICER and Swift/XRT data, we find that MAXI J1820+070 went from the hard-intermediate to the soft state in less than one day. The covariance ratios derived from NICER data show an increase toward lower energies, which indicate that the source should make a transition to the soft state. This transition finally took place, after MAXI J1820+070 stayed in the hard state at rather constant luminosity for about 116 days. The steepness of the increase of the covariance ratios is not correlated with the amount of rms variability and it does not show a monotonic evolution along the outburst.

A connection between accretion states and the formation of ultrarelativistic outflows in a neutron star X-ray binary

The nearby accreting neutron star binary Sco X-1 is the closest example of ongoing relativistic jet production at high Eddington ratios. Previous radio studies have revealed that alongside mildly relativistic, radio-emitting ejecta, there is at times a much faster transfer of energy from the region of the accretion flow along the jet. The nature of this ultrarelativistic flow remains unclear and while there is some evidence for a similar phenomenon in other systems which might contain neutron stars, it has never been observed in a confirmed black hole system. We have compared these previous radio observations with a new analysis of simultaneous X-ray observations which were performed with the RXTE mission. We find that the ejection of the ultra-relativistic flow seems to be associated with the simultaneous appearance of two particular types of quasi-periodic oscillations in the X-ray power spectrum. In contrast, the mildly relativistic, radio-emitting outflows may be associated with flat-topped broad band noise in the X-ray power spectrum. This is the first time a link, albeit tentative, has been found between these mysterious unseen flows and the accretion flow from which they are launched.

INSIGHT-HXMT Observations of the New Black Hole Candidate MAXI J1535−571: Timing Analysis

Abstract We present X-ray timing results of the new black hole candidate MAXI J1535−571 during its 2017 outburst from Hard X-ray Modulation Telescope (Insight-HXMT) observations taken from 2017 September 6 to 23. Following the definitions given by Belloni, we find that the source exhibits transitions from the low/hard state to the hard intermediate state, and eventually to the soft intermediate state. Quasi-periodic oscillations (QPOs) are found in the intermediate states, which suggest different types of QPOs. With the large effective area of Insight-HXMT at high energies, we are able to present the energy dependence of the QPO amplitude and centroid frequency up to 100 keV, which has rarely been explored by previous satellites. We also find that the phase lag at the type-C QPOs centroid frequency is negative (soft lag) and strongly correlated with the centroid frequency. Assuming a geometrical origin of type-C QPOs, the source is consistent with being a high-inclination system.

ON THE GEOMETRIC NATURE OF LOW-FREQUENCY QUASI-PERIODIC OSCILLATIONS IN NEUTRON-STAR LOW-MASS X-RAY BINARIES

We report on a detailed analysis of the so-called ~1 Hz quasi-periodic oscillation (QPO) in the eclipsing and dipping neutron-star low-mass X-ray binary EXO 0748-676. This type of QPO has previously been shown to have a geometric origin. Our study focuses on the evolution of the QPO as the source moves through the color-color diagram, in which it traces out an atoll-source-like track. The QPO frequency increases from ~0.4 Hz in the hard state to ~25 Hz as the source approaches the soft state. Combining power spectra based on QPO frequency reveals additional features that strongly resemble those seen in non-dipping/eclipsing atoll sources. We show that the low-frequency QPOs in atoll sources and the ~1 Hz QPO in EXO 0748-676 follow similar relations with respect to the noise components in their power spectra. We conclude that the frequencies of both types of QPOs are likely set by (the same) precession of a misaligned inner accretion disk. For high-inclination systems, like EXO 0748-676, this results in modulations of the neutron-star emission due to obscuration or scattering, while for lower-inclination systems the modulations likely arise from relativistic Doppler boosting and light-bending effects.

ACCRETION DISK DYNAMO AS THE TRIGGER FOR X-RAY BINARY STATE TRANSITIONS

Magnetohydrodynamic accretion disk simulations suggest that much of the energy liberated by the magnetorotational instability (MRI) can be channeled into large-scale toroidal magnetic fields through dynamo action. Under certain conditions, this field can dominate over gas and radiation pressure in providing vertical support against gravity, even close to the midplane. Using a simple model for the creation of this field, its buoyant rise, and its coupling to the gas, we show how disks could be driven into this magnetically dominated state and deduce the resulting vertical pressure and density profiles. Applying an established criterion for MRI to operate in the presence of a toroidal field, we show that magnetically supported disks can have two distinct MRI-active regions, separated by a "dead zone" where local MRI is suppressed, but where magnetic energy continues to flow upward from the dynamo region below. We suggest that the relative strengths of the MRI zones, and the local poloidal flux, determine the spectral states of X-ray binaries. Specifically, "intermediate" and "hard" accretion states occur when MRI is triggered in the hot, upper zone of the corona, while disks in "soft" states do not develop the upper MRI zone. We discuss the conditions under which various transitions should take place and speculate on the relationship of dynamo activity to the various types of quasi-periodic oscillations that sometimes appear in the hard spectral components. The model also explains why luminous accretion disks in the "soft" state show no signs of the thermal/viscous instability predicted by standard alpha models.

A SPECTRAL STUDY OF THE RAPID TRANSITIONS OF TYPE-B QUASI-PERIODIC OSCILLATIONS IN THE BLACK HOLE TRANSIENT XTE J1859+226

The evolution of different types of quasi-periodic oscillations (QPOs) and the coupled radiative/physical changes in the accretion disk are still poorly understood. In a few black hole binaries it was found that fast evolution of QPOs is associated with spectral variations. Such studies in other black hole binaries are important to understand the QPO phenomenon. For the black hole transient XTE J1817-330, we study fast QPO transitions and accompanying spectral variations to investigate what causes the spectral variation during the QPO transition. Roy et al. (2011) found QPOs in ten RXTE observations of XTE J1817-330. We found that, among the ten observations, only one observation shows erratic dips in its X-ray light curve. The power density spectra and the corresponding energy spectra were extracted and analyzed for the dip and non-dip sections of the light curve. We found that type-B $\sim$6 Hz QPO changes into type-A QPO in a few tens of seconds along with a flux decrease. This transient evolution is accompanied with a significant spectral variation. We report a transient QPO feature and accompanying spectral variation in XTE J1817-330. Based on our findings, we discuss the origin of fast evolution of QPOs and spectral variations.

Relations between X-ray timing features and spectral parameters of Galactic black hole X-ray binaries

We present a study of correlations between spectral and timing parameters for a sample of black hole X-ray binary candidates. Data are taken from GX 339-4, H 1743-322, and XTE J1650-500, as the Rossi X-ray Timing Explorer (RXTE) observed complete outbursts of these sources. In our study we investigate outbursts that happened before the end of 2009 to make use of the high-energy coverage of the HEXTE detector and select observations that show a certain type of quasi-periodic oscillations (type-C QPOs). The spectral parameters are derived using the empirical convolution model simpl to model the Comptonized component of the emission together with a disc blackbody for the emission of the accretion disc. Additional spectral features, namely a reflection component, a high-energy cut-off, and excess emission at 6.4 keV, are taken into account. Our investigations confirm the known positive correlation between photon index and centroid frequency of the QPOs and reveal an anticorrelation between the fraction of up-scattered photons and the QPO frequency. We show that both correlations behave as expected in the "sombrero" geometry. Furthermore, we find that during outburst decay the correlation between photon index and QPO frequency follow a general track, independent of individual outbursts.

Fast transition of type-B quasi-periodic oscillation in the black hole transient XTE J1817-330

Context. The evolution of different types of quasi-periodic oscillations (QPOs) and the coupled radiative/physical changes in the accretion disk are still poorly understood. In a few black hole binaries it was found that fast evolution of QPOs is associated with spectral variations. These studies in other black hole binaries are important to understand the QPO phenomenon. Aims. We study fast QPO transitions and accompanying spectral variations of the black hole transient XTE J1817-330 to investigate the causes of the spectral variation during the QPO transition. Methods. Recently, QPOs in ten RXTE observations of XTE J1817-330 were found. We found that among these, only one observation shows erratic dips in its X-ray light curve. The power density spectra and the corresponding energy spectra were extracted and analyzed for the dip and non-dip sections of the light curve. Results. We found that type-B ∼6 Hz QPO changes into type-A QPO in a few tens of seconds along with a flux decrease. This transient evolution is accompanied by a significant spectral variation. Conclusions. We report a transient QPO feature and accompanying spectral variation in XTE J1817-330. Based on our findings, we discuss the origin of fast evolution of QPOs and spectral variations.

Dwarf nova oscillations and quasi-periodic oscillations in cataclysmic variables - III. A new kind of dwarf nova oscillation, and further examples of the similarities to X-ray binaries

We present measurements of the periods of Dwarf Nova Oscillations (DNOs) and Quasi-Periodic Oscillations (QPOs) in Cataclysmic Variable stars (CVs), many culled from published literature, but also others newly observed (in VZ Pyx, CR Boo, OY Car, Z Cha, AQ Eri, TU Men, HX Peg, CN Ori, V893 Sco, WX Hyi and EC2117-54). These provide data for 26 systems. We show that in general P_QPO ~ 15 P_DNO and that the correlation for CVs extends by three orders of magnitude lower in frequency the similar relationship found for X-Ray binaries. In addition, we have found that there is a second type of DNO, previously overlooked, which have periods ~ 4 times those of the regular DNOs (As well as those mined from publications, we have observed them in VW Hyi, OY Car, AQ Eri, V803 Cen, CR Boo, VZ Pyx, HX Peg and EC2117-54). Often both types of DNO coexist. Unlike the standard DNOs, the periods of the new type, which we refer to as longer period DNOs (lpDNOs), are relatively insensitive to accretion luminosity and can even appear in quiescence of dwarf novae. We interpret them as magnetically channelled accretion onto the differentially rotating main body of the white dwarf primary, rather than onto a rapidly slipping equatorial belt as in the case of the standard DNOs. This is supported by published measurements of v sin(i) for some of the primaries. Some similarities of the DNOs, lpDNOs and QPOs in CVs to the three types of QPO in X-Ray binaries (burst pulsation, high and low frequency QPOs) are noted.

Complex Phase Lag Behaviors of the 0.5–10 H[CLC]z[/CLC] Quasi-periodic Oscillations in GRS 1915+105

Through studying the hard lags between the soft (3.3-5.8 keV) and hard (13.0-41.0 keV) photons of the 0.5-10 Hz quasi-periodic oscillations (QPOs) in GRS 1915+105, we have classified them into three types: 0.5-2.0, 2.0-4.5, and 4.5-10 Hz QPOs. They are closely related to different temporal and spectral states. The first type of QPO (0.5-2 Hz) has positive hard lags at both the QPO fundamental and first harmonic frequencies. These QPOs were observed in the quiescent soft state. The second type of QPO (2-4.5 Hz) was also detected in the quiescent soft state; these QPOs have opposite signs of hard lags at the QPO fundamental and first harmonic frequencies. The third type (4.5-10 Hz), which showed up in medium soft quiescent/outburst states, does not have significant higher harmonic peaks. There is a smooth transition between these three types of QPO behaviors. We did not detect 0.5-10 Hz QPOs in the very soft state. We discuss some of the implications of these results.

The Complex Phase-Lag Behavior of the 3-12 Hz Quasi-Periodic Oscillations during the Very High State of XTE J1550-564.

We present a study of the complex phase-lag behavior of the low-frequency (<20 Hz) quasi-periodic oscillations (QPOs) in the X-ray transient and black hole candidate XTE J1550-564 during its very high state. We distinguish two different types of low-frequency QPOs, based on their coherence and harmonic content. The first type is characterized by a 6 Hz QPO with a Q (the QPO frequency divided by the QPO width) of less than 3 and with a harmonic at 12 Hz. The second type of QPO is characterized by a 6 Hz QPO with a Q-value of greater than 6 and with harmonics at 3, 12, 18, and possibly at 9 Hz. Not only are the Q-values and the harmonic content of the two types different, but their phase-lag behavior also differs. For the first type of QPO, the low-energy photons (<5 keV) of both the 6 Hz QPO and its harmonic at 12 Hz lag the hard energy photons (>5 keV) by as much as 1.3 rad. The phase lags of the second type of QPO are more complex. The soft photons (<5 keV) of the 3 and 12 Hz QPOs lag the hard photons (>5 keV) by as much as 1.0 rad. However, the soft photons of the 6 Hz QPO precede the hard ones by as much as 0.6 rad. This means that different harmonics of this type of QPO have different signs for their phase lags. This unusual behavior is hard to explain when the lags are due to light-travel time differences between the photons at different energies, e.g., in a Comptonizing region surrounding the area in which the QPOs are formed.

Discovery of a ∼1 Hz Quasi‐periodic Oscillation in the Low‐Mass X‐Ray Binary 4U 1746−37

We have discovered a ~1 Hz quasi-periodic oscillation (QPO) in the persistent X-ray emission and during type I X-ray bursts of the globular cluster source, dipper and low-mass X-ray binary (LMXB) 4U 1746-37. The QPO properties resemble those of QPOs found recently in the LMXB dippers 4U 1323-62, and EXO 0748-676, which makes 4U 1746-37 the third source known to exhibit this type of QPOs. We present evidence for X-ray spectral changes in this source similar to those observed in LMXBs referred to as atoll sources. We detect two states, a low intensity and spectrally hard state, and a higher intensity and spectrally soft state. This may explain the different spectral characteristics reported for 4U 1746-37 earlier. The high intensity state resembles the banana branch state of atoll sources. The QPOs are only seen in the low intensity state, and are absent when the source is in the banana branch. This strongly suggests that either the accretion disk or an extended central source change shape between the low intensity state and the banana branch. Twelve bursts were detected, of which 5 took place while the source was on the banana branch and 7 when the source was in the low intensity state. The bursts occurring on the banana branch had an e-folding time ~3 times longer than those which occurred in the low intensity state. Whereas previously detected dips showed only a decrease in count rate of ~15%, we found in one observation a dip in which the count rate dropped from ~200 counts per second to ~20 counts per second. This dip lasted only ~250 seconds, during which clear spectral hardening occured. This is the first time strong evidence for spectral changes during a dip are reported for this source.