Long term wide-band spectro-temporal studies of outbursting black hole candidate sources GX 339-4 and H 1743-322: AstroSat and NuSTAR results

TL;DR

This study provides a detailed spectro-temporal analysis of outbursting black hole candidates GX 339-4 and H 1743-322 using AstroSat and NuSTAR data, revealing their spectral state transitions, QPO behaviors, and accretion dynamics.

Contribution

It offers new insights into the spectral state transitions and QPO characteristics of these black hole sources using wide-band observations from AstroSat and NuSTAR.

Findings

GX 339-4 transitions from hard to soft state with increasing luminosity.

H 1743-322 transits from quiescent to hard state during outburst.

Type-C QPOs observed up to 40 keV in H 1743-322.

Abstract

We present a comprehensive spectro-temporal analyses of recurrent outbursting black hole sources GX 339$-$4 and H 1743$-$322 using available AstroSat and NuSTAR archival observations during 2016-2024. The nature of the outburst profiles of both sources are examined using long-term MAXI/GSC and Swift/BAT lightcurves, and failed as well as successful outbursts are classified. Wide-band (0.5-60 keV) spectral modelling with disc (diskbb) and Comptonized (Nthcomp) components indicates that GX 339-4 transits from hard ($kT_{bb}=0.12-0.77$ keV, $\Gamma_{nth}=1.54-1.74$ and $L_{bol}=0.91-11.56$\% $L_{Edd}$) to soft state ($kT_{in}~[\approx{kT}_{bb}]=0.82-0.88$ keV, $\Gamma_{nth}=1.46-3.26$, $L_{bol}=19.59-30.06\%L_{Edd}$) via intermediate state ($kT_{in}~[\approx{kT}_{bb}]=0.56-0.88$ keV, $\Gamma_{nth}=1.76-2.66$, $L_{bol}=2.90-16.09\%L_{Edd}$), whereas H 1743-322 transits from quiescent to hard state ($\Gamma_{nth}=1.57-1.71$, $L_{bol}=2.08-3.48\%L_{Edd}$). We observe type-B and type-C Quasi-periodic Oscillations (QPOs) in GX 339-4 with increasing frequencies ($0.10-5.37$ Hz) along with harmonics. For H 1743-322, prominent type-C QPOs are observed in frequency range 0.22-1.01 Hz along with distinct harmonics. Energy-dependent power spectral studies reveal that fundamental QPO and harmonics disappear beyond 20 keV in GX 339-4, whereas fundamental QPO in H 1743-322 persists up to 40 keV. We also observe that type-C $QPO_{rms}\%$ decreases with energy for both sources although such variations appear marginal for type-B QPOs. Additionally, we report non-monotonic behavior of photon index with plasma temperature and detection of annihilation line. Finally, we discuss the relevance of the observational findings in the context of accretion dynamics around black hole binaries.