A comprehensive study of time delay between optical/near-infrared and X-ray emissions in black hole X-ray binaries

TL;DR

This study analyzes time delays between optical/near-infrared and X-ray emissions in black hole X-ray binaries, revealing state-dependent lag patterns that inform accretion disk physics.

Contribution

It provides the first comprehensive analysis of multi-wavelength delays in multiple black hole binaries using cross-correlation methods.

Findings

During rising hard state, X-ray lags behind OIR by several days.

During decaying hard state, OIR lags behind X-ray by 6-35 days.

Time delays are explained by disk instability and viscous heating models.

Abstract

We conducted a comprehensive study of daily delays using multi-wavelength data from a sample of well-studied black hole X-ray binaries, specifically focusing on the sources GX 339-4, 4U 1543-47, and XTE J1550-564. The Interpolated Cross-Correlation Function method was employed to investigate the temporal relationship between the X-ray (Compton component) and optical-infrared (OIR) emissions. Our results show that during the rising hard state, the Compton emission consistently lags behind OIR emission for several days. In contrast, during the decaying hard state, the OIR emission lags behind the Compton emission by approximately 6 to 35 days. This measurement can potentially be used in models of accretion physics and disk instability. We explore the underlying mechanisms responsible for these time delays, highlighting the critical role of viscous heating in the accretion disk in generating OIR luminosity for these sources. The observed time delays during both the rising and decaying hard states are well explained by the disk instability model.