Physical constraints from near-infrared fast photometry of the black-hole transient GX 339-4

TL;DR

This study presents multi-epoch X-ray and IR fast photometry of the black-hole transient GX 339-4, revealing distinct evolution patterns in their power spectral densities and suggesting a jet-based IR emission model.

Contribution

First multi-epoch X-ray/IR fast photometry campaign on GX 339-4 revealing different PSD evolution, constraining IR emission models in black-hole transients.

Findings

X-ray PSD follows standard evolution patterns.

IR PSD remains constant with a high-frequency break at 0.63 Hz.

IR emission likely originates from a relativistic jet filtering short-timescale fluctuations.

Abstract

We present results from the first multi-epoch X-ray/IR fast-photometry campaign on the black-hole transient GX 339--4, during its 2015 outburst decay. We studied the evolution of the power spectral densities finding strong differences between the two bands. The X-ray power spectral density follows standard patterns of evolution, plausibly reflecting changes in the accretion flow. The IR power spectral density instead evolves very slowly, with a high-frequency break consistent with remaining constant at $0.63 \pm 0.03$ Hz throughout the campaign. We discuss this result in the context of the currently available models for the IR emission in black-hole transients. While all models will need to be tested quantitatively against this unexpected constraint, we show that an IR emitting relativistic jet which filters out the short-timescales fluctuations injected from the accretion inflow appears as the most plausible scenario.