Evidence for two-component flows around the black hole candidate XTE J1550−564 from spectral features during its 1998-1999 outburst

Dutta, Broja Gopal; Chakrabarti, Sandip K.

doi:10.1111/j.1365-2966.2010.16428.x

Cited by 3 publications

(1 citation statement)

References 33 publications

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“…The typical evolution of QPOs in transient black hole sources during outburst has been established for a long time (Chakrabarti et al 2005(Chakrabarti et al , 2009Debnath et al 2008Debnath et al , 2010Debnath et al , 2013Dutta & Chakrabarti 2010). This evolution suggests that certain specific physical mechanisms are in place which are responsible for the generation of QPOs day after day (Chakrabarti et al 2005(Chakrabarti et al , 2009Debnath et al 2008Debnath et al , 2010Debnath et al , 2013.…”

Section: Evolution Of Time Lags and Quasi-periodic Oscillationsmentioning

confidence: 99%

Temporal Variability From the Two-Component Advective Flow Solution and Its Observational Evidence

Dutta

Chakrabarti

2016

ApJ

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In the propagating oscillatory shock model, the oscillation of the post-shock region, i.e., the Compton cloud, causes the observed low-frequency quasi-periodic oscillations (QPOs). The evolution of QPO frequency is explained by the systematic variation of the Compton cloud size, i.e., the steady radial movement of the shock front, which is triggered by the cooling of the post-shock region. Thus, analysis of the energy-dependent temporal properties in different variability timescales can diagnose the dynamics and geometry of accretion flows around black holes. We study these properties for the high-inclination black hole source XTE J1550-564 during its 1998 outburst and the low-inclination black hole source GX 339-4 during its 2006-07 outburst using RXTE/PCA data, and we find that they can satisfactorily explain the time lags associated with the QPOs from these systems. We find a smooth decrease of the time lag as a function of time in the rising phase of both sources. In the declining phase, the time lag increases with time. We find a systematic evolution of QPO frequency and hard lags in these outbursts. In XTE J1550-564, the lag changes from hard to soft (i.e., from a positive to a negative value) at a crossing frequency (ν c ) of ∼3.4 Hz. We present possible mechanisms to explain the lag behavior of high and low-inclination sources within the framework of a single two-component advective flow model.

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Section: Evolution Of Time Lags and Quasi-periodic Oscillationsmentioning

confidence: 99%

Temporal Variability From the Two-Component Advective Flow Solution and Its Observational Evidence

Dutta

Chakrabarti

2016

ApJ

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Long-term X-ray observations of seyfert 1 galaxy ark 120: on the origin of soft-excess

Nandi

Chatterjee

Chakrabarti

et al. 2021

Monthly Notices of the Royal Astronomical Society

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We present the long-term X-ray spectral and temporal analysis of a ‘bare-type AGN’ Ark 120. We consider the observations from XMM-Newton, Suzaku, Swift, and NuSTAR from 2003 to 2018. The spectral properties of this source are studied using various phenomenological and physical models present in the literature. We report (a) the variations of several physical parameters, such as the temperature and the optical depth of the electron cloud, the size of the Compton cloud, and the accretion properties for the last fifteen years. The spectral variations are explained from the changes in the accretion dynamics; (b) the X-ray time delay between 0.2-2 keV and 3-10 keV light-curves exhibited zero-delay in 2003, positive delay of 4.71 ± 2.1 ks in 2013, and negative delay of 2.90 ± 1.26 ks in 2014. The delays are explained considering Comptonization, reflection, and light-crossing time; (c) the long term intrinsic luminosities, obtained using nthcomp, of the soft-excess and the primary continuum show a correlation with a Pearson Correlation Co-efficient of 0.90. This indicates that the soft-excess and the primary continuum originate from the same physical process. From a physical model fitting, we infer that the soft excess for Ark 120 could be due to a small number of scatterings in the Compton cloud. Using Monte-Carlo simulations, we show that indeed the spectra corresponding to fewer scatterings could provide a steeper soft-excess power-law in the 0.2-3 keV range. Simulated luminosities are found to be in agreement with the observed values.

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Accretion properties of a low-mass active galactic nucleus: UGC 6728

Nandi,

Naik,

Chatterjee

et al. 2024

Monthly Notices of the Royal Astronomical Society

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We present a comprehensive analysis of approximately 15 years (2006–2021) of X-ray observations of UGC 6728, a low-mass bare AGN, for the first time. Our study encompasses both spectral and temporal aspects of this source. The spectral properties of this source are studied using various phenomenological and physical models. We conclude that (a) the observed variability in X-ray luminosity is not attributed to the hydrogen column density (NH) as UGC 6728 exhibits a bare nucleus, implying a negligible NH contribution along the line of sight, and (b) the spectral slope in the X-ray band demonstrates a systematic variation over time, indicating a transition from a relatively hard state to a comparatively soft state. We propose that the underlying accretion dynamics around the central object account for this behaviour. By performing X-ray spectral fitting, we estimate the mass of the central supermassive black hole (SMBH) in UGC 6728 to be $M_{\rm BH}=(7.13\pm 1.23)\times 10^5$ M$_\odot$. Based on our spectral and temporal analysis, we suggest that UGC 6728 lacks a prominent Compton hump or exhibits a very subtle hump that remains undetectable in our analysis. Furthermore, the high-energy X-ray photons in this source are likely to originate from the low-energy X-ray photons through inverse Compton scattering in a Compton cloud, highlighting a connection between the emission in two energy ranges. We noticed a strong soft excess component in the initial part of our observations, which was later reduced substantially. This variation of soft excess is explained in view of accretion dynamics.

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Evidence for two-component flows around the black hole candidate XTE J1550−564 from spectral features during its 1998-1999 outburst

Cited by 3 publications

References 33 publications

Temporal Variability From the Two-Component Advective Flow Solution and Its Observational Evidence

Temporal Variability From the Two-Component Advective Flow Solution and Its Observational Evidence

Long-term X-ray observations of seyfert 1 galaxy ark 120: on the origin of soft-excess

Accretion properties of a low-mass active galactic nucleus: UGC 6728

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