Quasi-periodic Oscillations Research Articles

QPE or QPO? – Quasiperiodic activity in low-mass galaxy nuclei

ABSTRACT Quasiperiodic eruptions (QPEs) from low-mass galaxy centres may result from accretion from a white dwarf in a very eccentric orbit about the central massive black hole. Evolution under gravitational radiation losses reduces the separation and eccentricity. I note that below a critical eccentricity ecrit ≃ 0.97, the accretion disc’s viscous time-scale at pericentre passage is probably longer than the orbital period P, and periodic eruptive behaviour is no longer possible. These QPE descendant systems (QPEDs) are then likely to produce quasiperiodic oscillations rather than eruptions, varying more smoothly over the orbital cycle, with duty cycles ∼1. I identify 2XMM J123103.2+110648 (P ≃ 3.9 h) and (more tentatively) RE J1034+396 (P ≃ 1 h) as candidate systems of this type, and find agreement with their deduced eccentricities e < ecrit. The absence of eruptions and the lower accretion luminosities resulting from the smaller gravitational radiation losses may make QPED systems harder to discover. Ultimately they must evolve to have viscous times much longer than the orbital period, and either remain steady, or possibly have infrequent but large outbursts. The latter systems would be massive analogues of the soft X-ray transients produced by low stellar-mass X-ray binaries.

Dynamics of cubic–quintic nonlinear [formula omitted]-symmetry mechanical oscillators

In this paper, we investigate the dynamics of two mechanical coupled oscillators (MCO) with Parity-Time (PT)-symmetry i.e., one has gain and the other has an equal and opposite amount of loss. In the linear case, the eigenmodes and breaking points were determined. In the nonlinear case, the breaking point for soft cubic or quintic potential obtained numerically was also found analytically with perfect agreement. However, instead of the breaking point, for the hard cubic or quintic potential, it is noted a transition toward a regime of periodic or quasi-periodic stable oscillation with energy transfer from the loss oscillator to the gain oscillator. This latter result suggests very important applications within the framework of the optical cavities and waveguides.

Spectral and temporal studies of Swift J1658.2–4242 using AstroSat observations with the JeTCAF model

ABSTRACT We present the X-ray spectral and temporal analysis of the black hole X-ray transient Swift J1658.2–4242 observed by AstroSat. Three epochs of data have been analysed using the JeTCAF model to estimate the mass accretion rates and to understand the geometry of the flow. The best-fitting disc mass accretion rate ($\dot{m}_{\rm d}$) varies between $0.90^{+0.02}_{-0.01}$ and $1.09^{+0.04}_{-0.03}$$\dot{M}_{\rm Edd}$ in these observations, while the halo mass accretion rate changes from $0.15^{+0.01}_{-0.01}$ to $0.25^{+0.02}_{-0.01}$$\dot{M}_{\rm Edd}$. We estimate the size of the dynamic corona that varies substantially from $64.9^{+3.9}_{-3.1}$ to $34.5^{+2.0}_{-1.5}$ rg and a moderately high jet/outflow collimation factor stipulates isotropic outflow. The inferred high disc mass accretion rate and bigger corona size indicate that the source might be in the intermediate to soft spectral state of black hole X-ray binaries. The mass of the black hole estimated from different model combinations is ∼14 M⊙. In addition, we compute the quasi-periodic oscillation (QPO) frequencies from the model-fitted parameters, which match the observed QPOs. We further calculate the binary parameters of the system from the decay profile of the light curve and the spectral parameters. The estimated orbital period of the system is 4.0 ± 0.4 h by assuming the companion as a mid or late K-type star. Our analysis using the JeTCAF model sheds light on the physical origin of the spectrotemporal behaviour of the source, and the observed properties are mainly due to the change in both the mass accretion rates and absorbing column density.

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.

Quasi-periodic oscillations in the γ-ray light curves of bright active galactic nuclei

Context. The detection of quasi-periodic oscillations (QPOs) in the light curves of active galactic nuclei (AGNs) can provide insights into the physics of the super-massive black holes (SMBHs) powering these systems and could represent a signature of the existence of SMBH binaries, setting fundamental constraints on SMBH evolution in the Universe. Aims. The identification of long-term QPOs, characterized by periods on the order of several months to years, is particularly challenging and can only be achieved via all-sky monitoring instruments that provide unbiased, continuous light curves of astrophysical objects. The Fermi-LAT satellite, thanks to its monitoring observing strategy, is an ideal instrument for such a goal. Here, we aim to identify QPOs in the γ-ray light curves of the brightest AGNs within the Fermi-LAT catalog. Methods. We analyzed the light curves of the 35 brightest Fermi-LAT AGNs, including data from the beginning of the Fermi mission (August 2008) to April 2021, with energies from 100 MeV to 300 GeV. Two time binnings were investigated: 7 and 30 days. The search for quasi-periodic features was then performed using the continuous wavelet transform. The significance of the result was tested via Monte Carlo simulations of artificial light curves with the same power spectral density and probability distribution function as the original light curves. The significances were then corrected for the look-elsewhere effect and provided as post-trials. Results. We identified 24 quasars with candidate QPOs. Several of our candidates coincide with previous claims in the literature, namely: PKS 0537−441, S5 0716+714, Mrk 421, B2 1520+31, and PKS 2247−131. All our candidates are transient. The most significant multi-year QPO, with a period of about 1100 days, was observed in the quasar S5 1044+71. It is reported here for the first time.

Nonlinear Dynamics of Ion-Acoustic Waves in a Magnetized Plasma With Trapped Electrons

The dynamics of obliquely propagating ion-acoustic waves (IAWs) in a collisionless, magnetized plasma consisting of free and trapped electrons, having a vortex-like distribution and fluid ions immersed in an external static magnetic field, has been investigated. The reductive perturbation technique (RPT) has been used to derive a Schamel’s modified Laedke–Spatschek (S–LS) equation. Several nonlinear structures have been obtained, like solitary waves, periodic and quasi-periodic oscillations, as well as chaotic structures. The effects of the magnetic field strength, the wave propagation obliqueness, the Mach number, and the electrons trapping on these nonlinear structures have been explored. The increase in the magnetic field strength has been found to reduce the soliton width and enhance its amplitude, while the role of rising the trapping parameter is only to increase the solitary wave amplitude. For a relatively weak magnetic field, the increase in the Mach number may change the solitonic structure to a periodic oscillation and the latter to a quasi-periodic one, while the decrease in the propagation angle to the magnetic field direction may bring about the second transition (periodic <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rightarrow$</tex-math> </inline-formula> quasi-periodic). Furthermore, depending on the plasma parameters, the intensification of the magnetic field can lead to the transition from a quasi-periodic to a chaotic behavior of the electrostatic wave.

Flares, Jets, and Quasiperiodic Outbursts from Neutron Star Merger Remnants

Using numerical relativity simulations with a subgrid dynamo prescription to generate strong initial magnetic fields, we investigate the possibility of launching a jet-like outflow from the hypermassive neutron star (HMNS) during the early stages of the merger, prior to the remnant’s collapse to a black hole. We demonstrate that buoyant instabilities in the strongly magnetized HMNS can lead to a periodic emission of powerful electromagnetic flares shortly after the merger. These are followed by a collimated mildly relativistic outflow. Both types of outflows feature quasiperiodic kilohertz substructure. These early-time outflows may power precursors to short-duration gamma-ray bursts (sGRBs) or in some cases the entire sGRB. While the overall temporal power spectrum we find broadly agrees with the one recently reported for quasiperiodic oscillations in the sGRB GRB910711, our simulations suggest that the periodic electromagnetic substructure is dominated by magnetohydrodynamic shearing processes rather than correlating with the corresponding postmerger gravitational-wave signal.

Nonlinear feedback synthesis and control of periodic, quasiperiodic, chaotic and hyper-chaotic oscillations in mechanical systems

Nonlinear feedback synthesis and control of periodic, quasiperiodic, chaotic and hyper-chaotic oscillations in mechanical systems

Influence of Filler Concentration on the Mechanical Properties of a Polymer Composite

The results of a study of carbon fiber-filled samples with an epoxy amine-cured matrix are presented. Independent quasi-periodic oscillations of the density and Young's modulus were recorded for the first time, against the backdrop of a monotonic increase in the strength of the samples. The probable causes of the appearance of the vibrational kinetics of the physico-mechanical parameters of the composite are determined depending on the content of the filler in the reaction volume of constant magnitude.

Detection of millihertz quasi-periodic oscillations in the low-mass X-ray binary 4U 1730–22 with NICER

ABSTRACT We report the discovery of millihertz quasi-periodic oscillations (mHz QPOs) from the neutron star (NS) low-mass X-ray binary 4U 1730–22 using the Neutron Star Interior Composition Explorer (NICER). After being inactive for almost 50 years, 4U 1730–22 went into outburst twice between June and August 2021, and between February and July 2022. We analyse all the NICER observations of this source, and detect mHz QPOs with a significance &amp;gt; 4 σ in 35 observations. The QPO frequency of the full data set ranged between ∼ 4.5 and ∼ 8.1 mHz with an average fractional rms amplitude of the order of ∼2 per cent. The X-ray colour analysis strongly suggests that 4U 1730–22 was in a soft spectral state during the QPO detections. Our findings are consistent with those reported for other sources where the mHz QPOs have been interpreted as the result of a special mode of He burning on the NS surface called marginally stable nuclear burning (MSNB). We conclude that the mHz QPOs reported in this work are also associated with the MSNB, making 4U 1730–22 the eighth source that shows this phenomenology. We discuss our findings in the context of the heat flux from the NS crust.

The optical behaviour of BL Lacertae at its maximum brightness levels: a blend of geometry and energetics

ABSTRACT In 2021 BL Lacertae underwent an extraordinary activity phase, which was intensively followed by the Whole Earth Blazar Telescope (WEBT) Collaboration. We present the WEBT optical data in the BVRI bands acquired at 36 observatories around the world. In mid-2021 the source showed its historical maximum, with R = 11.14. The light curves display many episodes of intraday variability, whose amplitude increases with source brightness, in agreement with a geometrical interpretation of the long-term flux behaviour. This is also supported by the long-term spectral variability, with an almost achromatic trend with brightness. In contrast, short-term variations are found to be strongly chromatic and are ascribed to energetic processes in the jet. We also analyse the optical polarimetric behaviour, finding evidence of a strong correlation between the intrinsic fast variations in flux density and those in polarization degree, with a time delay of about 13 h. This suggests a common physical origin. The overall behaviour of the source can be interpreted as the result of two mechanisms: variability on time-scales greater than several days is likely produced by orientation effects, while either shock waves propagating in the jet, or magnetic reconnection, possibly induced by kink instabilities in the jet, can explain variability on shorter time-scales. The latter scenario could also account for the appearance of quasi-periodic oscillations, with periods from a few days to a few hours, during outbursts, when the jet is more closely aligned with our line of sight and the time-scales are shortened by relativistic effects.

Nonlinear dynamics of pure intrinsic thermo-acoustic modes

In this paper the nonlinear dynamics of the pure Intrinsic Thermo-Acoustic (ITA) modes are experimentally investigated for burner stabilized premixed flames by decoupling them from the acoustic modes. Thereto, a setup is used with up- and downstream mufflers that provide close to anechoic boundary conditions. This enables the investigation of the self-excited oscillations of the flame, without the influences of acoustic reflections. An experimental bifurcation analysis is conducted to systematically investigate the different asymptotic oscillatory states and their transitions. By increasing the upstream velocity, the flame looses stability through a supercritical Hopf bifurcation and reveals limit cycles with a single dominant frequency. For increasing upstream velocity, a low frequent mode appears, resulting in quasi-periodic oscillations. This regime is characterized by a beating phenomenon with simultaneous amplitude and frequency modulations. When the upstream velocity is even further increased, a period doubling bifurcation is observed. To our best knowledge, the experimental investigation of the nonlinear dynamical behavior of pure ITA modes and, in particular, the low frequency oscillation, has not been reported before, and it provides valuable insights towards developing accurate time-domain models of the nonlinear acoustic behavior of premixed flames. Finally, a phenomenological model of two coupled oscillators is introduced that is able to qualitatively reproduce all observed nonlinear oscillations of the flames.

AstroSat and NuSTAR observations of XTE J1739−285 during the 2019–2020 outburst

ABSTRACT We report results from a study of XTE J1739−285, a transient neutron star low mass X-ray binary observed with AstroSat and NuSTAR during its 2019–2020 outburst. We detected accretion-powered X-ray pulsations at 386 Hz during very short intervals (0.5–1 s) of X-ray flares. These flares were observed during the 2019 observation of XTE J1739−285. During this observation, we also observed a correlation between intensity and hardness ratios, suggesting an increase in hardness with the increase in intensity. Moreover, a thermonuclear X-ray burst detected in our AstroSat observation during the 2020 outburst revealed the presence of coherent burst oscillations at 383 Hz during its decay phase. The frequency drift of 3 Hz during X-ray burst can be explained with r modes. Thus, making XTE J1739−285 belong to a subset of NS-LMXBs which exhibit both nuclear- and accretion-powered pulsations. The power density spectrum created using the AstroSat-laxpc observations in 2020 showed the presence of a quasi-periodic oscillation at ∼0.83 Hz. Our X-ray spectroscopy revealed significant changes in the spectra during the 2019 and 2020 outburst. We found a broad iron line emission feature in the X-ray spectrum during the 2020 observation, while this feature was relatively narrow and has a lower equivalent width in 2019, when the source was accreting at higher rates than 2020. Hard X-ray tail was observed during the 2019 observations, indicating the presence of non-thermal component in the X-ray spectra.

Precession and Lense-Thirring effect of hairy Kerr spacetimes

We investigate the frame-dragging effect of the hairy Kerr spacetimes on the spin of a test gyro and accretion disk. First, we analyze Lense-Thirring (LT) precession frequency, geodetic precession frequency, and the general spin precession frequency of a test gyro attached to a stationary observer in the spacetime. We find that the black hole hair suppresses those precession frequencies in comparison with that which occurs in Kerr spacetime in general relativity. Moreover, using those frequencies as a probe, we differentiate the hairy Kerr black hole (BH) from naked singularity (NS). Specifically, as the observer approaches the central source along any direction, the frequencies grow sharply for the hairy Kerr BH, while for the hairy NS they are finite except at the ring singularity. Then, we investigate the quasiperiodic oscillations (QPOs) phenomena as the accretion disk approaches the hairy Kerr BH or NS. To this end, we analyze the bound circular orbits and their perturbations. We find that as the orbits approach the corresponding innermost stable circular orbit (ISCO), both LT precession frequency and periastron precession frequency behave differently in the hairy Kerr BH and NS. Additionally, the hairy parameters have significant effects on the two frequencies. We expect that our theoretical studies could shed light on astrophysical observations in distinguishing hairy theories from Einstein's gravity, and also in distinguishing BH from NS in spacetime with hair.

Fast transitions of X-ray variability in the black hole transient GX 339−4: comparison with MAXI J1820+070 and MAXI J1348−630

ABSTRACT Fast transitions between different types of power density spectra (PDS) happening over time-scales of several tens of seconds are rare phenomena in black hole X-ray binaries. In this paper, we report a broad-band spectral-timing analysis of the fast transitions observed in the 2021 outburst of GX 339−4 using NICER and Insight-HXMT observations. We observe transitions between band-limited noise-dominated PDS and type-B quasi-periodic oscillations (QPOs), and their rapid appearance or disappearance. We also make a detailed comparison between the fast transitions in GX 339−4 with those seen in MAXI J1820+070 and MAXI J1348−630. By comparing the spectra of the periods with and without type-B QPOs, we find that the spectral ratios above 10 keV are nearly constant or slightly decreasing, and the values are different between sources. Below 10 keV, the flux change of the Comptonization component is inversely proportional to the flux change of the thermal component, suggesting that the appearance of type-B QPOs is associated with a redistribution of the accretion power between the disc and the Comptonizing emission region. The spectral ratios between the periods with type-B QPO and those with broad-band noise are significantly different from that with type-B QPO and without type-B QPO, where the ratios (type-B QPO/broad-band noise) show a maximum at around 4 keV and then decrease gradually towards high energies. Finally, we discuss the possible change of the geometry of the inner accretion flow and/or jet during the transitions.

Emergence of oscillatory cooperation in a population with incomplete information

Oscillatory behaviors are ubiquitous in nature and the human society. However, most previous works fail to reproduce them in the two-strategy game-theoretical models. Here we show that oscillatory behaviors naturally emerge if incomplete information is incorporated into the cooperation evolution of a non-Markov model. Specifically, we consider a population playing prisoner’s dilemma game, where each individual can only probabilistically get access to their neighbors’ payoff information and store them within their memory with a given length. They make their decisions based upon these memories. Interestingly, we find that the level of cooperation generally cannot stabilize but render quasi-periodic oscillation, and this observation is strengthened for a longer memory and a smaller information acquisition probability. The mechanism uncovered shows that there are misperceived payoffs of the player’s neighborhood, facilitating the growth of cooperators and defectors at different stages that leads to oscillatory behaviors as a result. Our findings are robust to the underlying structure of the population. Given the omnipresence of incomplete information, our findings may provide a plausible explanation for the phenomenon of oscillatory behaviors in the real world.

Correction to: Low-frequency quasi-periodic oscillation in MAXI J1820+070: Revealing distinct Compton and reflection contributions

Correction to: Low-frequency quasi-periodic oscillation in MAXI J1820+070: Revealing distinct Compton and reflection contributions

Search for X-Ray Quasiperiodicity of Six AGNs Using the Gaussian Process Method

The quasiperiodic oscillations (QPOs) found in active galactic nuclei (AGNs) are a very interesting observational phenomenon implying an unknown physical mechanism around supermassive black holes. Several AGNs have been found to have QPO phenomena in the X-ray energy band. Long-duration X-ray observations were collected and reduced for six AGNs with a suspected QPO. The Gaussian process model celerite was used to fit the light curves and to search for the quasiperiodicity behavior. The power spectral density and parameter posterior distributions of each light curve were calculated with the optimal model. Of the six AGNs, only RE J1034+396 was found to have a QPO of about 3600 s. The other five sources do not show QPO modulation behavior. We propose that a hot spot on the accretion disk is a possible physical mechanism resulting in this quasiperiodic behavior of AGNs.

A Geometric Model to Interpret the γ-Ray Quasiperiodic Oscillation of PG 1553+113

We propose a jet helical motion model to explain the γ-ray quasiperiodic oscillation of PG 1553+113. In this model, we hypothesize that a relativistic jet with constant angular velocity rotates around the axis, causing the Doppler factor of the jet to vary over time, leading to periodic changes in flux. In addition, we consider that the parameters of the emission field vary slightly during the observation period and can be obtained by directly fitting their multiwavelength spectra. Then, we use the resulting emission field information and the model to reproduce the light curve. Our model successfully explains the 2.18 ± 0.08 yr γ quasiperiodic oscillation of PG 1553+113, which is consistent with previous studies. Most importantly, we notice an upward trend in the light curve, and we suggest that this upward trend is due to long-term variability with a timescale of ∼42 yr.

Analysis and Forecast of the &lt;i&gt;Zeiraphera&lt;/i&gt; &lt;i&gt;griseana&lt;/i&gt; Dynamics Using the Delayed Moran-Ricker Model: the Impact of the Training Sample on Forecast Quality

We have applied the Moran–Ricker model with a time lag to describe the dynamics of two populations of larch bud moth. The model takes into account intrapopulation self-regulatory mechanisms. Data on populations inhabiting Switzerland in Graubunden (Baltensweiler, Fischlin, 1988; the Global Population Dynamics Database: Data set 1525) and Oberengadin (Baltensweiler, 1991) locations were used. We have found estimates of model parameter values by minimizing the sum of squared deviations of empirical and model trajectories. The point estimates of the population parameters were shown to satisfy the statistical criteria. The point estimates are located in the region of quasi-periodic oscillations, where, as a rule, they are adjacent to other dynamics modes. Consequently, the variation of population parameters caused by, for example, evolutionary processes or modifying factors influence can change the observed dynamics mode. To test the predictive properties of these models, we use the first part of the data to estimate the parameter values and the rest to compare the real dynamics with the model forecast. As it turned out, the quality of the forecast significantly depends on the nature of the dynamics at the end of the training sample used to estimate the parameters. The best prediction can be obtained if the training sample ends at the population peak phase. In the case of a low abundance phase, the forecast may have an acceptable error, but the nature of the predicted dynamics may change: for example, a shift in the population peak. For Data set 1525, we compare the point estimates obtained from a training sample of different lengths with the dynamic modes of the Moran–Riker model. This allows us to get an insight into the dynamic mode evolution in the Zeiraphera griseana population and to identify transitions from one dynamics mode to another.