Search

We study the spectral properties and accretion flow behavior of an ultraluminous X-ray source M82 X-1 using NuSTAR observations. We use the physical two-component advective flow (TCAF) model to fit the data and to derive the accretion flow properties of the source. From the model fitted parameters, we found that M82 X-1 is harboring an intermediate mass black hole at its centre, where the mass varies from 156. 04 - 15.30 + 13.51 to 380. 96 - 29.76 + 28.38 M ⊙ . The error weighed average mass of the black hole is 273 ± 43 M ⊙ , which accreted in nearly super-Eddington rate. The Compton cloud was compact with a size of ∼ 13 r g and the shock compression ratio had nearly intermediate values except for the epoch four. These indicate a possible significant mass outflow from the inner region of the disk. The quasi periodic oscillation (QPO) frequencies estimated from the model fitted parameters can reproduce the observed QPOs. The robustness of the model parameters is verified by drawing the confidence contours among them. [ABSTRACT FROM AUTHOR]

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 15 yr. The spectral variations are explained from the changes in the accretion dynamics; (b) the X-ray time delay between 0.2–2 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 coefficient 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. [ABSTRACT FROM AUTHOR]

We perform a comparative spectro-temporal analysis on the variability classes of GRS 1915+105 and IGR J17091-3624 to draw inferences regarding the underlying accretion flow mechanism. The ν , as well as C2 class Rossi X-ray Timing Explorer observation, have been considered for analysis. We investigate the intensity variation of the source in different energy domains that correspond to different components of the accretion flow and infer the relative dominance of these flow components during the dip/flare events. We correlate the dependence of the dynamic photon index (Θ) with intensities in different energy bands and comment on the transition of the source to hard/soft phases during soft dips/flares. We also report the presence of sharp QPOs at ∼ 7.1 Hz corresponding to both softer and harder domain in the case of ν variability class of GRS 1915+105 and discuss the possible accretion flow configuration it suggests. Sharp QPO around ∼ 20 mHz is observed in ν and C2 classes of IGR J17091-3624 in low and mid energy band (2.0–6.0 keV and 6.0–15.0 keV), but remains undetected in high energy (15.0–60.0 keV). The 2.5–25.0 keV background-subtracted spectra have also been fitted with TCAF along with a Compton reflection component. A plausible accretion flow mechanism in order to explain the observed variability has been proposed. [ABSTRACT FROM AUTHOR]