Interpreting the Spectro-Temporal Properties of the Black Hole Candidate Swift J151857.0-572147 during its First Outburst in 2024

TL;DR

This study analyzes the timing and spectral properties of the first outburst of the black hole candidate Swift J151857.0-572147 in 2024, revealing QPO characteristics, spectral state transitions, and potential accretion flow mechanisms.

Contribution

It provides the first detailed spectro-temporal analysis of Swift J151857.0-572147 during its 2024 outburst, including QPO detection up to 48 keV and insights into its spectral state evolution.

Findings

QPOs are of type C and detected up to 48 keV.

The source transitioned from an intermediate to a soft spectral state.

High hydrogen column density suggests local absorption effects.

Abstract

The transient Galactic black hole candidate Swift J151857.0-572147 went through an outburst in March 2024 for the first time. Using publicly archived {\it Insight}-HXMT data, we have analyzed the timing and spectral properties of the source. We have extracted the properties of the quasi-periodic oscillations (QPOs) by fitting the power density spectrum, which inferred that the QPOs are of type C. We have detected QPOs up to $\sim48$ keV using an energy dependence study of the QPOs. High-frequency QPO is not observed during this period. We also conclude that the oscillations of the shock in transonic advective accretion flows may be the possible reason for the origin of the QPOs. In the broad energy band of $2-100$ keV, simultaneous data from the three onboard instruments of \textit{Insight}-HXMT were used to perform spectral analysis. Different combinations of models, including broken power-law, multi-color disk blackbody, interstellar absorption, non-relativistic reflection in both neutral and ionized medium, and relativistic reflection were used to understand the spectral properties during the outburst. We discovered that at the beginning of the analysis period, the source was in an intermediate state and later transitioning toward the soft state based on the spectral parameters. It has a high hydrogen column density, which could be due to some local absorption to the source.