vKompth: A variable Comptonisation model for low-frequency quasi-periodic oscillations in black-hole X-ray binaries

Abstract

Low mass X-ray binaries (LMXBs) show strong variability over a broad range of time scales. The analysis of this variability, in particular of the quasi-periodic oscillations (QPO), is key to understanding the properties of the innermost regions of the accretion flow in these systems. We present a time-dependent Comptonisation model that fits the energy-dependent rms-amplitude and phase-lag spectra of low-frequency QPOs in black-hole (BH) LMXBs. We model the accretion disc as a multi-temperature blackbody source emitting soft photons which are then Compton up-scattered in a spherical corona, including feedback of Comptonised photons that return to the disc. We compare our results with those obtained with a model in which the seed-photons source is a spherical blackbody: at low energies the time-averaged, rms and phase-lag spectra are smoother for the disk-blackbody than for a blackbody, while at high energies both models give similar spectra. In general, we find that the rms increases with energy, the slope of the phase-lag spectrum depends strongly on the feedback, while the minimum-lag energy is correlated with the disc temperature. We fit the model to a 4.45-Hz type-B QPO in the BH LMXB MAXI J1438-630 and find statistically-better fits and more compatible parameters with the steady-state spectrum than those obtained with a blackbody seed-photons source. Furthermore, we successfully apply the model to the type-C QPO in the BH LMXB GRS 1915+105, and thus conclude that this variable-Comptonisation model reproduces the rms and phase-lags of both type B and C low-frequency QPOs in BH LMXBs.

12 pages, 7 figures, accepted for publication in MNRAS

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Cited by in corpus (24)

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• A variable corona during the transition from type-C to type-B quasi-periodic oscillations in the black hole X-ray binary MAXI J1820+070
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• Fast transitions of X-ray variability in the black hole transient GX 339--4: comparison with MAXI J1820+070 and MAXI J1348-630
• Wavelet analysis of the transient QPOs in MAXI J1535$-$571 with Insight-HXMT
• A hidden quasi-periodic oscillation in Cygnus X-1 revealed by NICER
• The nature of an imaginary quasi-periodic oscillation in the soft-to-hard transition of MAXI J1820+070
• A broadband spectral-timing study of QPOs in the bright black hole X-ray binary Swift J1727.8-1613
• High energy Millihertz quasi-periodic oscillations in 1A 0535+262 with Insight-HXMT challenge current models
• Timing analysis of the black-hole candidate Swift J1727.8-1613: detection of a dip-like feature in the high-energy cross spectrum
• Exploring the broadband spectral and timing characteristics of GRS 1915+105 with AstroSat and NICER observations
• Detection of a strong ~2.5 Hz modulation in the Newly Discovered Millisecond Pulsar MAXI J1816-195
• Evolution of the Comptonizing medium of the black-hole candidate Swift J1727.8$-$1613 along the hard to hard-intermediate state transition using NICER
• Spectro-temporal Investigation of Quasi-periodic Oscillations From Black Hole X-ray Binary 4U 1630-472 Using $\text{NICER}$
• Black-hole X-ray binary Swift J1727.8$-$1613 shows simultaneous Type-B and Type-C quasi-periodic oscillations across the hard-intermediate and soft-intermediate states
• Detection of a Type-C QPO during the soft-to-hard transition in Swift J1727.8-1613
• Variable QPO lags and reduced coherence between the disc and corona in MAXI J1820+070
• Radiative feedbacks as drivers for quasi-periodic-oscillation activity in black-hole X-ray binaries
• Spectro-temporal evolution of 4U 1702-429 using AstroSat-NICER
• Accretion Geometry of Black Hole X-ray Binaries: Insights from X-ray Observations
• QPO signatures of disk restoration after type-I X-ray bursts from 4U~1636$-$536
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