Multiwavelength View of Black Hole X-ray Binary Swift J151857.0-572147

Abstract

We investigate multiwavelength timing and spectral properties of the newly discovered black hole X-ray binary Swift J151857.0-572147 during its 2024 outburst using observations from AstroSat, NuSTAR, NICER, Swift, and MeerKAT. The AstroSat/LAXPC20 power density spectrum reveals a $\sim$8 Hz low-frequency QPO with a quality factor of $\sim2.8$. The broadband X-ray spectrum of the source exhibits prominent reflection features, which are modeled to constrain the geometry and physical properties of the accretion disk. The spectral analysis indicates that the source was in the soft/intermediate spectral state, characterized by a steep power law with a photon index of $Γ\approx 2.6$ and a relatively high disk temperature of $\sim0.9$ keV. The reflection modeling suggests a disk inclination of $23-31^{\circ}$ and a highly ionized accretion disk with $\logξ\sim 3.3$-4.0. The MeerKAT monitoring revealed a strong radio variability that closely tracked the hard X-ray evolution, including a bright radio flare during the hard-to-soft state transition, supporting close coupling between the accretion flow and jet activity. Using the quasi-simultaneous AstroSat, Swift/XRT and MeerKAT observations, we investigated the radio/X-ray correlation and found that Swift J151857.0-572147 follows the established $L_{\rm X}$-$L_{\rm R}$ relation for Galactic black hole X-ray binaries. Its location in the $L_{\rm X}$-$L_{\rm R}$ plane is consistent with that of Galactic black hole X-ray binaries, further supporting its black hole nature.