No abstract

Aims. We study the spectral evolution of the H1743−322 during outbursts in the RXTE era. We aim to connect the variation of the spectral parameters with the accretion parameters along with the progress of the outbursts. We understand the evolution of the accretion parameters and hence the dynamics of the accretion process in light of the irradiated disc instability model. Methods. We provide a comprehensive study of all the outbursts of H1743−322 between 2003 and 2011. We performed spectral modelling of all the RXTE/PCA observations using phenomenological models. Also, we carried out spectral modelling by a hydrodynamic accretion flow model and estimated the accretion parameters. We applied the irradiated disc instability scenario in the presence of both Keplerian and sub-Keplerain accretion components to understand the evolution of accretion parameters. For this purpose, we propose a toy model for the time variation of the accretion rates following a powerlaw during outbursts. Results. All of the outbursts show spectral state transitions in the hardness-intensity diagram. The 2003 and 2004 outbursts are long-duration outbursts and relatively softer than the other outbursts. The 2008b and 2011 outbursts provide a unique opportunity to estimate the critical accretion rate (ṁdc) for triggering an outburst in this system within a narrow range of 0.076 < ṁdc < 0.086 (in Eddington units). In the absence of any dynamical measurement, we attempt to constrain a few orbital parameters of the system using an assumed mass and ṁdc in the range.

We present the results on broadband X-ray properties of persistent black hole binaries GRS 1758−258 and 1E 1740.7−2942 using AstroSat, NuSTAR and Swift-XRT observations carried out during 2016−2022. We perform spectral modeling of both sources after eliminating the contamination in their LAXPC spectra from nearby X-ray sources. Preliminary spectral modelling using Comptonization and line emission (∼ 6.4 keV) models suggest that GRS 1758−258 occupies both dim-soft state (kTbb = 0.37 ± 0.01 keV, Γ ∼ 5.9, $L_{bol}=1\%$ of Eddington luminosity LEdd) and hard state (Γ = 1.64 − 2.22, kTe=4−45 keV, Lbol=1−5% LEdd) that requires a multi-colour disc blackbody model (kTin = 0.54 ± 0.01 keV) occasionally. 1E 1740.7−2942 instead is found only in hard state (Γ=1.67−2.32, kTe=5−16 keV, Lbol=1−2% LEdd). Reflection properties of both sources are studied by applying relativistic reflection model RELXILL to the broadband spectra. Our results from AstroSat and NuSTAR consistently unveiled the presence of a Comptonizing region along with an ionized reflection region (ionization parameter logξ=2.7−3.8 and 2.7−4.7 erg cm s−1 in GRS 1758−258 and 1E 1740.7−2942 respectively) in both sources. Reflection modeling revealed GRS 1758−258 to have a high metal abundance ($A_{fe}=3.9^{+0.4}_{-0.3}$ times solar metal abundance) and inclination angle (i) of 61 ± 2○. In case of 1E 1740.7−2942, i is constrained to be 55 ± 1○. Finally, we discuss the implication of our findings in the context of accretion dynamics by comparing our results with the previous studies.