A timing view of the additional high-energy spectral component discovered in the black hole candidate Swift J1727.8-1613

TL;DR

This paper analyzes energy-dependent quasi-periodic oscillations in the black hole binary Swift J1727.8-1613, revealing a high-energy rms excess likely linked to jet emission and precession.

Contribution

It reports the first detection of a high-energy rms excess in a black hole X-ray binary and suggests a jet origin for the additional spectral component.

Findings

High-energy rms exceeds low-energy rms above 40 keV.

An extra hard spectral component is observed beyond standard models.

The HE-rms excess correlates with jet-related flux and parameters.

Abstract

We present an energy-dependent analysis for the type-C quasi-periodic oscillations (QPOs) observed in the black hole X-ray binary Swift J1727.8-1613 using Insight-HXMT observations. We find that the QPO fractional rms at energies above 40 keV is significantly higher than that below 20 keV. This is the first report of a high energy (HE)-rms excess in the rms spectrum of a black hole X-ray binary. In the high energy band, an extra hard component is observed in additional to the standard thermal Comptonization component at similar energy band. The value of the QPO HE-rms excess is not only correlated with the disk parameters and the photon index of the standard Comptonization component, but also exhibits a moderate positive correlation with the flux of the additional hard spectral component. No features in the QPO phase-lag spectra are seen corresponding to the additional hard component. We propose that the additional hard component in the spectrum may originate from jet emission and the associated QPO HE-rms excess can be explained by the precession of the jet base.