Correlations between QPO frequencies and spectral parameters of GRS 1915+105 using AstroSat observations

TL;DR

This study investigates the relationship between QPO frequencies and spectral parameters in GRS 1915+105 using AstroSat data, confirming some theoretical predictions while noting quantitative deviations.

Contribution

It provides observational evidence linking QPO frequencies to relativistic dynamical models across a wide range of accretion states in GRS 1915+105.

Findings

C-type QPO frequencies follow the relativistic dynamical frequency trend

High-frequency QPOs at 70 Hz also follow the same trend

Quantitative deviations from the model are discussed

Abstract

In this work, we study the correlation between Quasi-periodic Oscillation (QPO) frequency and the spectral parameters during various X-ray states in the black hole binary GRS 1915+105 which matches well with the predicted relativistic dynamic frequency (i.e. the inverse of the sound crossing time) at the truncated radii. We have used broadband data of LAXPC and SXT instruments onboard AstroSat. Spectral fitting shows that the accretion rate varies from $\sim 0.1$ to $\sim 5.0 \times 10^{18}$ gm/s and the truncated radius changing from the last stable orbit of an almost maximally spinning black hole, $\sim$ 1.2 to $\sim$ 19 Gravitational radii. For this wide range, the frequencies of the C-type QPO (2 - 6 Hz) follow the trend predicted by the relativistic dynamical frequency model and interestingly, the high-frequency QPO at $\sim$ 70 Hz also follows the same trend, suggesting they originate from the innermost stable circular orbit with the same mechanism as the more commonly observed C-type QPO. While the qualitative trend is as predicted, there are quantitative deviations between the data and the theory, and the possible reasons for these deviations are discussed.