Accretion properties of soft X-ray transient XTE J1856+053 during its 2023 Outburst

TL;DR

This study analyzes the 2023 outburst of the soft X-ray transient XTE J1856+053, revealing spectral states, accretion disk properties, and indicating a high-spin black hole as the central object.

Contribution

It provides detailed timing and spectral analysis of XTE J1856+053 during its outburst, highlighting a rapid state transition and evidence for a high-spin black hole.

Findings

No quasi-periodic oscillations detected.

Spectral fitting indicates a high-spin black hole.

Rapid transition from soft to intermediate state.

Abstract

Soft X-ray transients are a subclass of the low mass X-ray binaries that occasionally show a sudden rise in their soft X-ray luminosity; otherwise, they remain in an extremely faint state. We investigate the accretion properties of the soft X-ray transient XTE J1856+053 during its 2023 outburst obtained by NICER and NuSTAR data in July. We present detailed results on the timing and spectral analysis of the X-ray emission during the outburst. The power spectral density shows no quasi-periodic oscillation features. The source's spectrum on July 19 can be well-fitted with a multi-color blackbody component, a power-law component, and a reflection component with a broadened iron emission line. NICER spectra can be well-fitted by considering a combination of a blackbody and a power-law. The source exhibits a transition within just five days from a soft state to an intermediate state during the outburst decline phase. The inner accretion disk has a low inclination angle ($\sim18^\circ$). The spectral analysis also suggests a high-spin ($a>0.9$) BH as the central accreting object.