A two-component Comptonization model for the type-B QPO in MAXI J1348−630

Abstract

Spectral-timing analysis of the fast variability observed in X-rays is a powerful tool to study the physical and geometrical properties of the accretion/ejection flows in black hole (BH) binaries. The origin of type-B quasi-periodic oscillations (QPO), predominantly observed in BH candidates in the soft-intermediate state, has been linked to emission arising from the relativistic jet. In this state, the X-ray spectrum is characterized by a soft-thermal blackbody-like emission due to the accretion disc, an iron emission line (in the 6–7 keV range), and a power-law-like hard component due to inverse-Compton scattering of the soft-photon source by hot electrons in a corona or the relativistic jet itself. The spectral-timing properties of MAXI J1348−630 have been recently studied using observations obtained with the NICER observatory. The data show a strong type-B QPO at ∼4.5 Hz with increasing fractional rms amplitude with energy and positive lags with respect to a reference band at 2–2.5 keV. We use a variable-Comptonization model that assumes a sinusoidal coherent oscillation of the Comptonized X-ray flux and the physical parameters of the corona at the QPO frequency, to fit simultaneously the energy-dependent fractional rms amplitude and phase lags of this QPO. We show that two physically connected Comptonization regions can successfully explain the radiative properties of the QPO in the full 0.8–10 keV energy range.

NICER uncovers the transient nature of the type-B quasi-periodic oscillation in the black hole candidate MAXI J1348−630

“…However, when nthcomp / total 40% (or diskbb / total 60%), the type-B QPO disappeared. García et al (2021) found that the energy-dependent fractional rms and phase lags of the type-B QPO in MAXI J1348−630 can be well modelled with a two-component Comptonisation model. Given that Figs.…”

“…Type-B QPOs were detected in the SIMS at a stable frequency of ∼4.5 Hz. Belloni et al (2020) studied the energy dependence of the fractional rms and phase lags of the type-B QPO using NICER data, and García et al (2021) successfully fitted them simultaneously with a twocomponent Comptonisation model. Jithesh et al (2021) studied the energy dependence of the fractional rms of a type-C QPO using simultaneous AstroSat and NICER observations.…”

Spectral and timing evolution of MAXI J1631–479 during the 2018–19 outburst with NICER

“…Motta et al (2015) and van den Eijnden et al (2017) have demonstrated the inclination dependence of Type-C QPOs. Type-B and A QPOs, however, are not dependent on inclination and thus could have a different origin (García et al 2021). Ingram et al (2009) and Ingram & Done (2011) have shown that the QPO frequency is strongly anti-correlated with the outer radius of the hot flow, which is nothing but the truncation radius between the thin and thick disk.…”

“…Time-dependent Comptonization models were developed to explain the various phenomenology of kilo-Hertz QPOs in neutron star low mass X-ray binaries (Lee & Miller 1998;Kumar & Misra 2014;Karpouzas et al 2020). Recently, García et al (2021) extended this model to explain the rms amplitude and phase lag spectra of Type-B QPOs in the BHB MAXI J1348-630 by incorporating two separate Comptonization regions. Under the assumption that there is a dynamical mechanism that excites the oscillations, García et al (2021) were able to explain the radiative properties, rms and lag spectra, of the Type-B QPO in this source.…”

“…Recently, García et al (2021) extended this model to explain the rms amplitude and phase lag spectra of Type-B QPOs in the BHB MAXI J1348-630 by incorporating two separate Comptonization regions. Under the assumption that there is a dynamical mechanism that excites the oscillations, García et al (2021) were able to explain the radiative properties, rms and lag spectra, of the Type-B QPO in this source. While most of the models based on intrinsic variability are quite different from each other, the other class of models based on geometric effects attempt to explain the QPOs with the phenomenon of Lense-Thirring precession.…”