A Minimal Time Scale for the Spectral States of GX 339-4

TL;DR

This paper identifies a minimal timescale in GX 339-4's spectral states using RXTE data, linking it to inner disk radius and variability measures, providing a new way to study black hole transient dynamics.

Contribution

It introduces a minimal timescale for spectral states and demonstrates its correlation with inner disk radius and variability features, offering a novel diagnostic tool.

Findings

Positive correlation between minimal timescale and inner disk radius.

The minimal timescale correlates with break frequencies in power spectra.

The timescale relates to traditional variability measures like RMS.

Abstract

Black hole transients are known to undergo spectral transitions that form q-shaped tracks on a hardness intensity diagram. In this work, we use archival RXTE data to extract a characteristic minimal timescale for the spectral states in GX 339-4 for the 2002-3, and 2010 outbursts. We use the extracted timescale to construct an intensity variability diagram for each outburst. This new diagram is comparable to the traditional hardness intensity diagram and offers the potential for probing the underlying dynamics associated with the evolution of the relevant emission regions in black hole transients. We confirm this possibility by connecting the minimal timescale with the inner disk radius, $R_{in}$ (estimated from spectral fits), and demonstrate a positive correlation between these variables as the system evolves through its spectral transitions. Furthermore, we probe the relation between the minimal timescale and the break frequencies extracted from the power spectral densities. Lastly, we examine a possible link between the extracted timescale and a traditional measure of variability i.e., the root mean square, determined directly from the power spectra.