Related papers: X-ray variability and correlations in the two phas…
The broadband X-ray emission from type 1 active galactic nuclei, dominated by a powerlaw continuum, is thought to arise from repeated inverse Compton scattering of seed optical/UV photons by energetic electrons in a hot corona. The seed…
We find a very strong correlation between the intrinsic spectral slope in X-rays and the amount of Compton reflection from a cold medium in Seyfert AGNs and in hard state of X-ray binaries with either black holes or weakly-magnetized…
We test accurate models of Comptonization spectra over the high quality data of the BeppoSAX long look at NGC 5548, allowing for different geometries of the scattering region, different temperatures of the input soft photon field and…
Understanding disc-corona geometry through X-ray reverberation variability studies in Seyfert galaxies is crucial, yet our knowledge mostly relies on flux-averaged mean spectral analysis. In this study, we investigate the origin of the…
We develop the power spectral density (PSD) model to explain the nature of the X-ray variability in IRAS 13224-3809, including the full effects of the X-ray reverberation due to the lamp-post source. We utilize 16 XMM-Newton observations…
Utilizing a range of techniques including multi-band light curves, softness ratio analysis, structure functions, rms spectra, cross-correlation functions, and ratios of spectra from different intervals, we present a comprehensive study of…
Warm coronae, thick ($\tau_{\mathrm{T}}\approx 10$-$20$, where $\tau_{\mathrm{T}}$ is the Thomson depth) Comptonizing regions with temperatures of $\sim 1$ keV, are proposed to exist at the surfaces of accretion discs in active galactic…
We discuss the origin of the dramatically different X-ray spectral shapes observed in the Low Hard State (LHS: dominated by thermal comptonisation) and the High Soft State (HSS: dominated by the accretion disc thermal emission and…
We calculate the radiation spectrum and its time variability of the black hole accretion disk-corona system based on the three-dimensional magnetohydrodynamic simulation. In explaining the spectral properties of active galactic nuclei…
We have modelled the X-ray emission of T Tauri stars assuming that they have isothermal, magnetically-confined coronae. These coronae extend outwards until either the pressure of the hot coronal gas overcomes the magnetic field, or, if the…
In paper 1 (Cheng et al. 2001) we have shown that the soft X-ray spectra of two types of Seyfert 1 galaxies statistically vary differently with increasing intensity. In order to understand how the spectrum of blazars changes, the spectral…
X-ray spectral timing analysis is presented of XMM-Newton observations of the narrow line Seyfert 1 galaxy I Zwicky 1 (I Zw 1) taken in 2015 January. After exploring the effect of background flaring on timing analyses, X-ray time lags…
The 1.5 Seyfert galaxy NGC 3227 has been observed by several X-ray missions. We carried out a combined analysis of the data obtained by more recent major observations of the source: two observations performed by XMM-Newton in 2000 and 2006…
It is believed that the hard X-ray emission in the luminous active galactic nuclei (AGNs) is from the hot corona above the cool accretion disk. However, the formation of the corona is still debated. Liu et al. investigated the spectrum of…
Hard X-rays observed in Active Galactic Nuclei (AGNs) are thought to originate from the Comptonization of the optical/UV accretion disk photons in a hot corona. Polarization studies of these photons can help to constrain the corona geometry…
We performed a detailed spectral and timing analysis of a Seyfert 1 galaxy Mrk 509 using data from the Neil Gehrels Swift observatory that spanned over ~13 years between 2006 and 2019. To study the variability properties from the optical/UV…
Relativistically blurred reflection from the accretion disc provides a powerful probe of the extreme environments close to supermassive black holes; the inner regions of the accretion flow and the corona that produces the intense X-ray…
Understanding the persistent emission is crucial for studying type I X-ray bursts, which provide insight into neutron star properties. Although accretion disc coronae appear to be common in many accreting systems, their fundamental…
We model an accretion disk atmosphere and corona photoionized by a central X-ray continuum source. We calculate the opacity and radiation transfer for an array of disk radii, to obtain the two-dimensional structure of the disk and its X-ray…
We develop a new spectral model for the broadband spectral energy distribution (SED) of Active Galactic Nuclei (AGN). This includes an outer standard disc, an inner warm Comptonising region to produce the soft X-ray excess and a hot corona.…