Looking for the elusive 3:2 ratio of high-frequency quasi-periodic oscillations in the microquasar XTE J1550-564

TL;DR

This study analyzed about 30 observations of XTE J1550-564's outbursts to investigate the frequencies of high-frequency QPOs, finding no evidence for the expected 3:2 ratio, thus constraining theoretical models.

Contribution

It provides the first systematic analysis of HFQPO frequencies in XTE J1550-564, challenging the previously claimed 3:2 ratio and setting new constraints for theoretical models.

Findings

No confirmed 3:2 frequency ratio in HFQPOs

Two potential 3σ detections of HFQPO pairs

Established constraints for HFQPO models

Abstract

Using the two main XTE J1550-564 outbursts (1998-99 and 2000) we gathered about 30 observations with confirmed detections of HFQPOs. While this is a small sample it is enough to start looking at the generic properties of these oscillations, especially focusing on their frequencies and their potential harmonic relationship. This then will provide us with a list of constraints, necessary for any attempt of modelling their origin. We defined five groups based on their similarities in the Fourier domain, namely the continuum of their power density spectra (PDS) and the HFQPO frequencies. We then combined the individual PDSs of each family to obtain a PDS with higher statistics to search for other potential, previously undetected, weaker peaks. While we have two $3\sigma$ potential detections of a pair of HFQPOs in our combined PDSs, none of them shows HFQPOs with frequencies in a previously claimed 3:2 ratio. Using the results presented here we propose an updated list of requirements for any model trying to explain the HFQPOs in microquasars.