A microquasar classification from a disk instability perspective

TL;DR

This paper proposes a physically motivated classification of microquasar states based on disk instabilities and associated Quasi-Periodic Oscillations, aiming to unify their observed behaviors through underlying physical processes.

Contribution

It introduces a new classification framework linking disk instabilities to microquasar states, based on theoretical and observational analysis of Quasi-Periodic Oscillations.

Findings

Identified four theoretical states from three disk instabilities.

Compared these states with observed spectral states of microquasars.

Provided a model-independent way to classify microquasar behavior.

Abstract

The spectacular variability of microquasars has led to a long string of efforts in order to classify their observed behaviors in a few states. The progress made in the understanding of the Quasi-Periodic Oscillations observed in these objects now makes it possible to develop a new way to find order in their behavior, based on the theorized physical processes associated with these oscillations. This will also have the interest of reuniting microquasars in a single classification based on the physical processes at work and therefore independent of their specificities (mass, variation timescale, outburst history, etc.). This classification is aimed to be a tool to further our understanding of microquasars behavior and not to replace phenomenological states. We start by considering three instabilities that can cause accretion in the disk. We compare the conditions for their development, and the Quasi-Periodic Oscillations they can be expected to produce, with the spectral states in which these Quasi-Periodic Oscillations are observed and sometimes coexist. From the three instabilities that we proposed to explain the three states of GRS 1915+105 we actually found the theoretical existence of four states. We compared those four states with observations and also how those four states can be seen in a model-independent fashion. Those four state can be used to find an order in microquasar observations, based on the properties of the Quasi-Periodic Oscillations and the physics of the associated instabilities.