Hard Intermediate State Research Articles

Large and complex X-ray time lags from black hole accretion disks with compact inner coronae

Abstract Black hole X-ray binaries in their hard and hard-intermediate states display hard and soft time lags between broadband noise variations (high-energy emission lagging low-energy and vice versa), which could be used to constrain the geometry of the disk and Comptonising corona in these systems. Comptonisation and reverberation lag models, which are based on light-travel delays, can imply coronae which are very large (hundreds to thousands of gravitational radii, Rg) and in conflict with constraints from X-ray spectral modelling and polarimetry. Here we show that the observed large and complex X-ray time lags can be explained by a model where fluctuations are generated in and propagate through the blackbody-emitting disk to a relatively compact (∼10 Rg) inner corona. The model naturally explains why the disk variations lead coronal variations with a Fourier-frequency dependent lag at frequencies <1 Hz, since longer variability time-scales originate from larger disk radii. The propagating fluctuations also modulate successively the coronal seed photons from the disk, heating of the corona via viscous dissipation and the resulting reverberation signal. The interplay of these different effects leads to the observed complex pattern of lag behaviour between disk and power-law emission and different power-law energy bands, the energy-dependence of power-spectral shape, and a strong dependence of spectral-timing properties on coronal geometry. The observed spectral-timing complexity is thus a natural consequence of the response of the disk-corona system to mass-accretion fluctuations propagating through the disk.

Impact of reflection Comptonization on x-ray reflection spectroscopy: The case of EXO 1846-031

Within the disk-corona model, it is natural to expect that a fraction of reflection photons from the disk are Compton scattered by the hot corona (reflection Comptonization), even if this effect is usually ignored in x-ray reflection spectroscopy studies. We study this effect by using NICER and NuSTAR data of the Galactic black hole EXO 1846-031 in the hard-intermediate state with the model . Our analysis suggests that a scattered fraction of order 10% is required to fit the data, but the inclusion of reflection Comptonization does not change appreciably the measurements of key parameters like the black hole spin and the inclination angle of the disk. Published by the American Physical Society 2024

Evolution of QPOs in GX 339–4 and EXO 1846–031 with Insight-HXMT and NICER

We conduct a spectral and timing analysis of GX 339−4 and EXO 1846−031 with the aim of studying the evolution of type-C quasiperiodic oscillations (QPOs) with spectral parameters. The high-cadence data from Insight-HXMT and NICER allow us to track the evolution of QPOs and spectra simultaneously. Type-C QPOs appear at the end of the low–hard state and/or the hard–intermediate state. Our results reveal that the QPO frequency is closely related to the inner disk radius and mass accretion rate in the two sources. This correlation aligns well with the dynamic frequency model of a truncated disk.

INTEGRAL/IBIS polarization detection in the hard and soft intermediate states of Swift J1727.8−1613

Aims. Soft γ-ray emission (100 keV–10 MeV) has previously been detected in the hard state of several microquasars. In some sources, this emission was found to be highly polarized and was suggested to be emitted at the base of the jet. Until now, no γ-ray polarization had been found in any other state. Methods. Using INTEGRAL/IBIS, we studied the soft γ-ray spectral and polarization properties of Swift J1727.8−1613 throughout its outburst. Results. We detect a highly polarized spectral component in both the hard intermediate state and the early stages of the soft intermediate state above 210 keV. In the hard intermediate state, the polarization angle significantly deviates from the compact jet angle projected onto the sky, whereas in the soft intermediate they are closely aligned. This constitutes the first detection of jet-aligned polarization in the soft γ-ray for a microquasar. We attribute this polarized spectral component to synchrotron emission from the jet, which indicates that some of the jet might persist into the softer states.

The role of outflows in black-hole X-ray binaries

The hot inner flow in black-hole X-ray binaries is not just a static corona rotating around the black hole: it must be partially outflowing. It is therefore a mildly relativistic ``outflowing corona.'' We have developed a model in which Comptonization takes place in this outflowing corona. In all of our previous work, we assumed a rather high outflow speed of $0.8c$. Here, we investigate whether an outflow with a significantly lower speed can also reproduce the observations. Thus, in this work we consider an outflow speed of $0.1c$ or less. As in all of our previous work, we used a Monte Carlo code to compute not only the emergent X-ray spectra, but also the time lags that are introduced to the higher-energy photons with respect to the lower-energy ones via multiple scatterings. We also record the angle (with respect to the symmetry axis of the outflow) and the height at which photons escape. Our results are very similar to those of our previous work, with some small quantitative differences that can be easily explained. We are again able to quantitatively reproduce five observed correlations: (a) the time lag as a function of Fourier frequency, (b) the time lag as a function of photon energy, (c) the time lag as a function of Gamma , (d) the time lag as a function of the cutoff energy in the spectrum, and (e) the long-standing radio--X-ray correlation -- and all of them with only two parameters, which vary in the same ranges for all the correlations. Our model does not require a compact, narrow relativistic jet, although its presence does not affect the results. The essential ingredient of our model is the parabolic shape of the Comptonizing corona. The outflow speed plays a minor role. Furthermore, the bottom of the outflow, in the hard state, looks like a ``slab'' to the incoming soft photons from the disk, and this can explain the observed X-ray polarization, which is along the outflow. In the hard-intermediate state, we predict that the polarization of GX 339-4 will be perpendicular to the outflow.

Accretion flow dynamics and characteristics of MAXI J153–571-spectral analysis using combination of XSPEC and TCAF models

MAXI J153–571 accretion flow consists of Keplerian (optically thick) and sub-Keplerian (optically thin) flow, and their mass accretion rates seem to regulate other accretion flow characteristics. Hard X-rays are produced when the Keplerian seed soft photons are thermally or inverse comptonized in the Compton cloud/post-shock region by hot electrons. The variations/fluctuations of components of the accretion flow during the hard states create propagating Quasi-periodic oscillation (QPO) when their timescales are roughly matched and resonance phenomena occur. The QPO and its frequency are timing properties and the accretion flow spectra-temporal characteristics can be determined via spectral analysis. In this study, we looked into the accretion flow characteristics of MAXI J153–571 during the hard-intermediate state. Spectral analysis of MAXI J153–571 observed by MAXI/GSC, Swift/BAT, and NuSTAR on the same or close-in epochs was carried out. XSPEC and TCAF models were used in fitting/modeling the data. A robust and statistically acceptable fit spectra with a reduced Chi-squared value of ∼ 0.84 – 1.20 and best-fit photon index of 2.0–2.29 was obtained. The track of the accretion flow characteristics was obtained using models’–fitted parameters and MATLAB written codes of physical equations. Some accretion flow characteristics are positively correlated while others are anti-correlated at different phases and their correlation are statistically significant. The correlation of accretion flow characteristics with one another suggests that saturation effects, variation/fluctuations in the accretion flow, and intermittent/flickering behavior of MAXI J153–571 are tied to the variations/fluctuations of the intrinsic properties; mass accretion rates. Moreover, a resonance condition of 0.70 to 0.83 indicates that the cooling and infall timescales are roughly matched and affirms the presence of QPO in the accretion flow. This suggests that the origin of the photon index–QPO frequency (Γ–vQPO) relation is strongly linked to the variation/fluctuations in mass accretion flow rates. Hence, the accretion flow is dynamic, and independent variations/fluctuations of mass accretion rates could regulate the variation/fluctuations of other accretion flow parameters and perhaps, spectral evolution.

Tracking the X-Ray Polarization of the Black Hole Transient Swift J1727.8–1613 during a State Transition

We report on an observational campaign on the bright black hole (BH) X-ray binary Swift J1727.8–1613 centered around five observations by the Imaging X-ray Polarimetry Explorer. These observations track for the first time the evolution of the X-ray polarization of a BH X-ray binary across a hard to soft state transition. The 2–8 keV polarization degree decreased from ∼4% to ∼3% across the five observations, but the polarization angle remained oriented in the north–south direction throughout. Based on observations with the Australia Telescope Compact Array, we find that the intrinsic 7.25 GHz radio polarization aligns with the X-ray polarization. Assuming the radio polarization aligns with the jet direction (which can be tested in the future with higher-spatial-resolution images of the jet), our results imply that the X-ray corona is extended in the disk plane, rather than along the jet axis, for the entire hard intermediate state. This in turn implies that the long (≳10 ms) soft lags that we measure with the Neutron star Interior Composition ExploreR are dominated by processes other than pure light-crossing delays. Moreover, we find that the evolution of the soft lag amplitude with spectral state does not follow the trend seen for other sources, implying that Swift J1727.8–1613 is a member of a hitherto undersampled subpopulation.

Discovery of evolving low-frequency QPOs in hard X-rays (∼100 keV) observed in black hole Swift J1727.8−1613 with AstroSat

ABSTRACT We report the first detection of evolving low-frequency quasi-periodic oscillation (LFQPO) frequencies in hard X-rays upto 100 keV with AstroSat/LAXPC during ‘unusual’ outburst phase of Swift J1727.8−1613 in hard intermediate state (HIMS). The observed LFQPO in 20–100 keV has a centroid $\nu _{_{\rm QPO}}=1.43$ Hz, a coherence factor Q = 7.14 and an amplitude ${\rm rms_{_{\rm QPO}}} = 10.95{{\ \rm per\ cent}}$ with significance σ = 5.46. Type-C QPOs (1.09–2.6 Hz) are found to evolve monotonically during HIMS of the outburst with clear detection in hard X-rays (80−100 keV), where ${\rm rms_{_{\rm QPO}}}$ decreases ($\sim 12\!-\!3{{\ \rm per\ cent}}$) with energy. Further, $\nu _{_{\rm QPO}}$ is seen to correlate (anticorrelate) with low- (high-) energy flux in 2–20 keV (15–50 keV). Wide-band (0.7−40 keV) energy spectrum of NICER/XTI and AstroSat/LAXPC is satisfactorily described by the ‘dominant’ thermal Comptonization contribution (∼88 per cent) in presence of a ‘weak’ signature of disc emissions (kTin ∼ 0.36 keV) indicating the harder spectral distribution. Considering source mass $M_{\rm BH}=10\, \mathrm{M}_\odot$ and distance 1.5 < d (kpc) < 5, the unabsorbed bolometric luminosity is estimated as $\sim 0.03\!-\!0.92{{\ \rm per\ cent}}\, L_{\rm Edd}$. Finally, we discuss the implications of our findings in the context of accretion dynamics around black hole X-ray binaries.

Dramatic Drop in the X-Ray Polarization of Swift J1727.8–1613 in the Soft Spectral State

Black hole X-ray binaries exhibit different spectral and timing properties in different accretion states. The X-ray outburst of a recently discovered and extraordinarily bright source, Swift J1727.8–1613, has enabled the first investigation of how the X-ray polarization properties of a source evolve with spectral state. The 2–8 keV polarization degree was previously measured by the Imaging X-ray Polarimetry Explorer (IXPE) to be ≈4% in the hard and hard intermediate states. Here we present new IXPE results taken in the soft state, with the X-ray flux dominated by the thermal accretion disk emission. We find that the polarization degree has dropped dramatically to ≲1%. This result indicates that the measured X-ray polarization is largely sensitive to the accretion state and the polarization fraction is significantly higher in the hard state when the X-ray emission is dominated by upscattered radiation in the X-ray corona. The combined polarization measurements in the soft and hard states disfavor a very high or low inclination of the system.

Magnetic Flux Plays an Important Role during a Black Hole X-Ray Binary Outburst in Radiative Two-temperature General Relativistic Magnetohydrodynamic Simulations

Black hole (Bh) X-ray binaries cycle through different spectral states of accretion over the course of months to years. Although persistent changes in the Bh mass accretion rate are generally recognized as the most important component of state transitions, it is becoming increasingly evident that magnetic fields play a similarly important role. In this article, we present the first radiative two-temperature general relativistic magnetohydrodynamics simulations in which an accretion disk transitions from a quiescent state at an accretion rate of Ṁ∼10−10ṀEdd to a hard-intermediate state at an accretion rate of Ṁ∼10−2ṀEdd . This huge parameter space in mass accretion rate is bridged by artificially rescaling the gas density scale of the simulations. We present two jetted BH models with varying degrees of magnetic flux saturation. We demonstrate that in “standard and normal evolution” models, which are unsaturated with magnetic flux, the hot torus collapses into a thin and cold accretion disk when Ṁ≳5×10−3ṀEdd . On the other hand, in “magnetically arrested disk” models, which are fully saturated with vertical magnetic flux, the plasma remains mostly hot with substructures that condense into cold clumps of gas when Ṁ≳1×10−2ṀEdd . This suggests that the spectral signatures observed during state transitions are closely tied to the level of magnetic flux saturation.

The First Polarimetric View on Quasiperiodic Oscillations in a Black Hole X-Ray Binary

We present the first polarimetric analysis of quasiperiodic oscillations (QPOs) in a black hole binary utilizing IXPE data. Our study focuses on Swift J1727.8–1613, which experienced a massive outburst that was observed by various telescopes across different wavelengths. The IXPE observation we studied was conducted during the hard-intermediate state. The polarization degree (PD) and polarization angle (PA) were measured at 4.28% ± 0.20% and 1.°9 ± 1.°4, respectively. Remarkably, significant QPO signals were detected during this observation, with a QPO frequency of approximately 1.34 Hz and a fractional rms amplitude of about 12.3%. Furthermore, we conducted a phase-resolved analysis of the QPO using the Hilbert–Huang transform technique. The photon index showed a strong modulation with respect to the QPO phase. In contrast, the PD and PA exhibit no modulations in relation to the QPO phase, which is inconsistent with the expectation of the Lense–Thirring precession of the inner flow. Further theoretical studies are needed to conform with the observational results.

NICER, NuSTAR, and Insight-HXMT Views to the Newly Discovered Black Hole X-Ray Binary Swift J1727.8-1613

Swift J1727.8–1613 is a black hole X-ray binary newly discovered in 2023. We perform spectral analysis with simultaneous Insight-HXMT, NICER, and NuSTAR observations when the source was approaching the hard intermediate state. Such a joint view reveals an additional hard component apart from the normally observed hard component with reflection in the spectrum, to be distinguished from the usual black hole X-ray binary systems. By including this extra component in the spectrum, we have measured a high spin of 0.98−0.07+0.02 and an inclination of around 40−0.8+1.2 °, which is consistent with NICER results reported before. However, we find that the additional spectral component cannot be exclusively determined due to the model degeneracy. Accordingly, a possible jet/corona configuration is adjusted to account for the spectral fitting with different model trials. The extra component may originate either from a relativistic jet or a jet base/corona underneath a slow jet.

High-soft to Low-hard State Transition in Black Hole X-Ray Binaries with GRMHD Simulations

To understand the decaying phase of outbursts in the black hole (BH) X-ray binaries (BH-XRBs), we performed very long general relativistic magnetohydrodynamic simulations of a geometrically thin accretion disk around a Kerr BH with slowly rotating matter injected from outside. We thoroughly studied the flow properties, dynamical behavior of the accretion rate, magnetic flux rate, and jet properties during the temporal evolution. Due to the interaction between the thin disk and injected matter, the accretion flow near the BH goes through different phases. The sequence of phases is: soft state → soft-intermediate state → hard-intermediate state → hard state → quiescent state. For the accretion rate (and hence the luminosity) to decrease (as observed) in our model, the mass injection should not decay slower than the angular momentum injection. We also observed quasiperiodic oscillations (QPOs) in the accretion flow. Throughout the evolution, we observed low-frequency QPOs (∼10 Hz) and high-frequency QPOs (∼200 Hz). Our simple unified accretion flow model for state transitions is able to describe outbursts in BH-XRBs.

A quantitative explanation of the radio – X-ray correlation in black-hole X-ray binaries

Context. The observed correlation between the radio and X-ray fluxes in the hard state of black-hole X-ray binaries (BHXRBs) has been in existence for over two decades. It is currently accepted that the hard X-rays in BHXRBs come from Comptonization in the corona and the radio emission from the relativistic jet (Lorentz γ ≫ 1), which is a narrow structure of a few Rg = GM/c2 at its base. The jet and the corona, however, are separate entities with hardly any communication between them, apart from the fact that both are fed from the accreting matter. Aims. It is also widely accepted that the accretion flow around the black holes in BHXRBs consists of a thin outer disk and a hot inner flow. From this hot inner flow, which has a positive Bernoulli integral, an outflow must emanate in the hard and hard-intermediate states of the source. By considering Compton up-scattering of soft disk photons in the outflow (i.e., in the outflowing “corona”, which is a wider structure of tens to hundreds of Rg at its base) as the mechanism that produces the hard X-ray spectrum, we have been able to quantitatively explain a number of observed correlations. Here, we investigate whether this outflowing corona can also explain the observed radio – X-ray correlation. We remark that the outflowing corona (wide, with a low Lorentz γ) is completely separate from the relativistic jet (narrow, with a high Lorentz γ). The two may coexist, with the jet at the rotation axis and the corona around it. Methods. We considered parabolic outflow models, which we have successfully used in the explanation of other correlations regarding GX 339-4 in the hard and hard-intermediate states, and computed the radio emission at 8.6 GHz coming from them, as well as the power-law photon-number spectral index Γ of the Comptonized hard X-rays produced in them. Thus, we have a correlation between the computed radio flux FR at 8.6 GHz and the computed spectral index Γ of the hard X-ray spectrum. This correlation is a theoretical prediction, since both FR and Γ are computed from the model and, to our knowledge, no such correlation has been constructed from observations. This prediction can be confirmed or proven wrong in future outbursts of GX 339-4. Based upon observations, we also produced a correlation between the observed hard X-ray flux FX and the observed index Γ. Thus, for each value of Γ, observed or computed, we have the corresponding values of the observed FX and the computed FR, which we plotted against each other. Results. For GX 339-4, we found that our model calculations for FR and Γ, with Γ as the link between the observed FX and the computed FR, successfully reproduce the observed correlation of FR ∝ FX0.6 in the hard state. In addition, in the hard-intermediate state of GX 339-4, this correlation breaks down and we predict that, in future outbursts of the source, the FR will exhibit first a sudden increase and then a sharp drop within a very narrow range of values of FX. Such a sharp drop of the FR has been observed in other sources. Conclusions. In our picture both the radio and the hard X-ray emission come from the same region, namely the outflow, and it is therefore not surprising that they are correlated. Since in a parabolic outflow with constant outflow speed the density is largest at its bottom, the soft photons, coming from below, see something appearing similar to a “slab”, with a moderate optical depth (up to ten in the hard state) along the outflow and an order of magnitude larger in the perpendicular direction. We remark that it is a slab geometry that is invoked to explain the observed X-ray polarization from BHXRBs. Because of this, we predict that the X-ray polarization of GX 339-4 will be parallel to the outflow in the hard state and perpendicular to it in the hard-intermediate state.

The origin of long soft lags and the nature of the hard-intermediate state in black hole binaries

ABSTRACT Fast variability of the X-ray corona in black hole binaries can produce a soft lag by reverberation, where the reprocessed thermalized disc photons lag behind the illuminating hard X-rays. This lag is small, and systematically decreases with increasing mass accretion rate towards the hard–soft transition, consistent with a decreasing truncation radius between the thin disc and X-ray hot inner flow. However, the soft lag suddenly increases dramatically just before the spectrum becomes disc dominated (hard-intermediate state). Interpreting this as reverberation requires that the X-ray source distance from the disc increases dramatically, potentially consistent with switching to X-rays produced in the radio jet. However, this change in lag behaviour occurs without any clear change in hard X-ray spectrum, and before the plasmoid ejection event that might produce such a source (soft-intermediate state). Instead, we show how the soft lag can be interpreted in the context of propagation lags from mass accretion rate fluctuations. These normally produce hard lags, as the model has radial stratification, with fluctuations from larger radii modulating the harder spectra produced at smaller radii. However, all that is required to switch the sign is that the hottest Comptonized emission has seed photons that allow it to extend down in energy below the softer emission from the slower variable turbulent region from the inner edge of the disc. Our model connects the timing change to the spectral change, and gives a smooth transition of the X-ray source properties from the bright hard state to the disc-dominated states.

Quasi-periodic Oscillations in GX 339−4 during the 2021 Outburst Observed with Insight-HXMT

A new outburst of GX 339−4 in 2021 was monitored by the Hard X-ray Modulation Telescope (Insight-HXMT). By using the data of Insight-HXMT from 2021 February to March, we make an X-ray timing analysis of this new outburst. Based on the results of the count rates, hardness–intensity diagram, and power density spectrum (PDS), we confirm that the source exhibits spectral transitions from the low-hard state (LHS) to the hard-intermediate state (HIMS). During the transition from the LHS to the HIMS, low-frequency quasi-periodic oscillations (QPOs) are detected in the PDS. We found that these QPOs are all type C QPOs with centroid frequencies evolving from 0.1 to 0.6 Hz in the LHS and in the 1–3 Hz frequency range in HIMS. The QPO features above 50 keV are reported for the first time in this black hole by Insight-HXMT. The QPO rms stays stable with time but decreases with energy at a higher energy above ∼10 keV. We also find that the phase lag of the type C QPO is close to zero in the early outburst stage but becomes positive as the outburst evolves, with a hard lag of ∼0.6–1.2 rad in 50–100 keV. The implications of the phase lag in high energy bands and the possible physical mechanisms to explain those observations are also discussed.

A Spectral-timing Study of the Inner Flow Geometry in MAXI J1535-571 with Insight-HXMT and NICER

We have performed a spectral-timing analysis of the black hole X-ray binary MAXI J1535-571 during its 2017 outburst, with the aim of exploring the evolution of the inner accretion flow geometry. X-ray reverberation lags are observed in the hard-intermediate state (HIMS) and soft-intermediate state of the outburst. During the HIMS, the characteristic frequency of the reverberation lags ν 0 (the frequency at which the soft lag turns to zero in lag–frequency spectra) increases when the spectrum softens. This reflects a reduction of the spatial distance between the corona and accretion disk, when assuming the measured time lags are associated with the light travel time. We also find a strong correlation between ν 0 and the type-C quasi-periodic oscillation (QPO) centroid frequency ν QPO, which can be well explained by the Lense–Thirring precession model under a truncated disk geometry. Despite the degeneracy in the spectral modeling, our results suggest that the accretion disk is largely truncated in the low hard state, and moves inward as the spectrum softens. Combine the spectral modeling results with the ν 0 – ν QPO evolution, we are inclined to believe that this source probably has a truncated disk geometry in the hard state.

Testing the dynamic origin of Quasi-periodic Oscillations in MAXI J1535−571 and H 1743−322

ABSTRACT We investigate spectro-temporal properties for two black hole X-ray binary sources, MAXI J1535−571 and H 1743−322, during their hard and hard-intermediate states. For MAXI J1535−571, we analyse swift/XRT, NuSTAR, and nicer observations, specifically focusing on the occurrence of type-C Quasi-periodic Oscillations (QPOs). Regarding H 1743−322, we analyse multi-epoch observations of nicer and AstroSat, identifying a type-C QPO with centroid frequency ranging from 0.1–0.6 Hz. In both sources, we fit the spectra with a relativistic truncated disc and a power-law component. In MAXI J1535−571, we also observe an additional relativistically smeared iron-line. Through temporal and spectral analysis, we estimate the QPO centroid frequency and spectral parameters, such as the accretion rate and inner disc radii. We test the origin of type-C QPOs as relativistic precession frequency, and dynamic frequency (i.e. the inverse of the sound crossing time $\frac{r}{c_\mathrm{ s}(r)}$). The dependence of QPO frequency on both the accretion rate and inner disc radii favours the QPO origin as dynamic frequency. We discuss the implications of these results.

The luminous, hard state can’t be MAD

ABSTRACT We present a straightforward argument for why the luminous, hard state of black hole X-ray binaries (BHXRBs) cannot always be associated with a magnetically arrested accretion disc (MAD). It relies on three core premises: (1) that the type-C quasi-periodic oscillation (QPO) is best explained by Lense–Thirring (LT) precession of a tilted, inner, hot flow; (2) that observed optical and infrared (IR) QPOs with the same or lower frequency as the type-C QPO suggest the jet, too, must precess in these systems; and (3) that numerical simulations of MADs show that their strong magnetic fields promote alignment of the disc with the black hole and, thereby, suppress LT precession. If all three premises hold true, then, at least whenever the optical and IR QPOs are observed alongside the type-C QPO, these systems cannot be in the MAD state. Extending the argument further, if the type-C QPO is always associated with LT precession, then it would rule out MADs anytime this timing feature is seen, which covers nearly all BHXRBs when they are in the luminous, hard and hard-intermediate states.

Timing analysis of the new black hole candidate MAXI J1803−298 with Insight–HXMT and NICER

ABSTRACT We present the timing analysis results of MAXI J1803−298, a black hole candidate, during its 2021 outburst using data obtained from the Insight–Hard X-ray Modulation Telescope (Insight–HXMT) and the Neutron star Interior Composition Explorer (NICER). Our analysis reveals that the source undergoes a state transition from the low hard state to the hard intermediate state, followed by the soft intermediate state, ultimately reaching the high soft state. We searched for the quasi-periodic oscillations (QPOs) and studied the characteristics of the outburst. At the beginning of the outburst, the source was in the hard state, many type-C QPOs were seen in the Insight–HXMT data, and the frequency of these QPOs increased from ∼0.16 to 2.6 Hz. Our analysis of the rms–frequency relationship of the type-C QPOs indicates a turning point in the frequency. We also analysed the phase lag versus frequency and energy relationship and deduced that the source likely has a high inclination angle, consistent with previous research. The observed rms and phase-lag features in type-C QPOs could be explained by the Lense–Thirring precession model, although alternatives would be still viable. The lag spectrum of type-B QPOs exhibits a U-shaped pattern similar to that of many other sources, and the type-B QPOs’ rms increases as the energy increases. This phenomenon can be explained by the dual-corona model.