Phase-resolved spectral analysis of the 11 millihertz quasi-periodic oscillation in the black-hole candidate H1743-322

TL;DR

This study performs phase-resolved spectroscopy on H1743-322 to investigate the origin of its unique mHz QPOs, revealing iron line flux modulation possibly linked to Lense-Thirring precession, enhancing understanding of black hole accretion physics.

Contribution

It provides the first phase-resolved spectral analysis of mHz QPOs in H1743-322, showing iron line flux modulation and proposing a precession-based origin.

Findings

Iron line flux modulated at twice the mHz QPO frequency.

Evidence supports Lense-Thirring precession as a possible mechanism.

Connection between mHz QPOs and type-C QPO properties discussed.

Abstract

H1743-322 is one of the few black hole candidates (BHCs) in low-mass X-ray binaries that shows mHz quasi-periodic oscillations (QPOs) that are not associated with the more common type A, B and C oscillations seen in the X-ray light curves of typical BHCs systems. To better understand the physical origin of the mHz oscillations, we carried out a phase-resolved spectroscopic study of two RXTE observations of this source. As previously reported, the averaged energy spectra of H1743-322 shows a strong iron line at $\sim6.5$ keV. Here we found evidence that the line flux appears to be modulated at twice the frequency of the mHz QPO. This line flux modulation is very similar to the one previously found for the type-C QPO in this source. We interpret the possibly periodic line flux modulation with this mHz QPO in terms of Lense-Thirring precession of the inner flow, and discuss the possible connection with the modulation of the line properties with the type-C QPO frequency.