Detection of the first infra-red quasi periodic oscillation in a black hole X-ray binary

TL;DR

This study reports the first detection of an infra-red quasi-periodic oscillation in a black hole X-ray binary, revealing correlations across IR, optical, and X-ray bands and suggesting a jet origin for the IR variability.

Contribution

It provides the first evidence of IR QPOs in a black hole binary and explores their relation to X-ray QPOs, advancing understanding of jet and accretion processes.

Findings

IR QPO detected at 0.08 Hz, half the X-ray QPO frequency

Strong IR/X-ray variability correlation with X-rays leading by 100 ms

Jet synchrotron emission likely responsible for IR QPO

Abstract

We present analysis of fast variability of Very Large Telescope/ISAAC (infra-red), \textit{XMM-Newton}/OM (optical) and EPIC-pn (X-ray), and RXTE/PCA (X-ray) observations of the black hole X-ray binary GX 339-4 in a rising hard state of its outburst in 2010. We report the first detection of a Quasi Periodic Oscillation (QPO) in the infra-red band (IR) of a black hole X-ray binary. The QPO is detected at 0.08 Hz in the IR as well as two optical bands (U and V). Interestingly, these QPOs are at half the X-ray QPO frequency at 0.16 Hz, which is classified as the type-C QPO; a weak sub-harmonic close to the IR and optical QPO frequency is also detected in X-rays. The broad band sub-second time scale variability is strongly correlated in IR/X-ray bands, with X-rays leading the IR by over 100 ms. This short time delay, shape of the cross correlation function and spectral energy distribution strongly indicate that this broad band variable IR emission is the synchrotron emission from the jet. A jet origin for the IR QPO is strongly favoured, but cannot be definitively established with the current data. The spectral energy distribution indicates a thermal disc origin for the bulk of the optical emission, but the origin of the optical QPO is unclear. We discuss our findings in the context of the existing models proposed to explain the origin of variability.