QPO Evolution in 2005 Outburst of the Galactic Nano Quasar GRO J1655-40

TL;DR

This paper analyzes the evolution of QPOs during the 2005 outburst of GRO J1655-40, revealing how the shock region in the accretion flow moves and accelerates, affecting the observed X-ray oscillations.

Contribution

It introduces a model linking QPO frequency evolution to shock movement in the accretion disk, providing new insights into the dynamics of black hole outbursts.

Findings

Shock moves inward during rise and outward during decline

QPO frequencies fit a shock oscillation model

Disk parameters like shock location and velocity are derived

Abstract

GRO J1655-40 showed significant X-ray activity in the last week of February, 2005 and remained active for the next 260 days. The rising and the decline phases of this particular outburst show evidence for systematic movements of the Comptonizing region, assumed to be a CENBOL, which causes the Quasi-periodic Oscillations or QPOs. We present both the spectral and the timing results of the RXTE/PCA data taken from these two hard spectral states. Assuming that the QPOs originate from an oscillating shock CENBOL, we show how the shock slowly moves in through the accretion flow during the rising phase at a constant velocity and accelerate away outward during the later part of the decline phase. By fitting the observed frequencies with our solution, we extract time variation of various disk parameters such as the shock locations, velocity etc.