Accretion flow behaviour during the evolution of the Quasi Periodic Oscillation Frequency of XTE J1550-564 in 1998 outburst

TL;DR

This study analyzes the evolution of QPO frequencies during the 1998 outburst of XTE J1550-564, revealing a systematic frequency drift explained by a propagatory oscillating shock model, providing insights into accretion flow dynamics.

Contribution

It presents a detailed analysis of QPO frequency evolution during an outburst and models it with a propagatory shock solution, offering new understanding of accretion flow behavior.

Findings

QPO frequency increased from 81mHz to 13.1Hz during the rising phase.

QPO frequency decreased and stabilized around 2.62Hz after peak.

The frequency drift is well explained by a propagatory oscillating shock model.

Abstract

Low and intermediate frequency quasi-periodic oscillations (QPOs) are thought to be due to oscillations of Comptonizing regions or hot regions embedded in Keplerian discs. Observational evidence of evolutions of QPOs would therefore be very important as they throw lights on the dynamics of the hotter region. Our aim is to find systems in which there is a well-defined correlation among the frequencies of the QPOs over a range of time so as to understand the physical picture. In this paper, we concentrate on the archival data of XTE J1550-564 obtained during 1998 outburst, and study the systematic drifts during the rising phase from the 1998 September 7 to the 1998 September 19, when the QPO frequency increased monotonically from 81mHz to 13.1Hz. Immediately after that, QPO frequency started to decrease and on the 1998 September 26, the QPO frequency became 2.62Hz. After that, its value remained almost constant. This frequency drift can be modelled satisfactorily with a propagatory oscillating shock solution where the post-shock region behaves as the Comptonized region. Comparing with the nature of a more recent 2005 outburst of another black hole candidate GRO 1655-40, where QPOs disappeared at the end of the rising phase, we conjecture that this so-called `outburst' may not be a full-fledged outburst.