On the harmonics of the low-frequency quasi-periodic oscillation in GRS 1915+105

TL;DR

This paper analyzes the low-frequency quasi-periodic oscillations and their harmonics in GRS 1915+105, revealing a positive correlation between frequency and broadening, which challenges traditional interpretations of these timing features.

Contribution

The study provides new insights into the harmonic content of LFQPOs by analyzing their frequency-width relationship, challenging existing models.

Findings

Positive trend of broadening with increasing frequency

Harmonics show a different behavior than expected

Results challenge traditional interpretations of LFQPOs

Abstract

GRS 1915+105 is a widely studied black hole binary, well known because of its extremely fast and complex variability. Flaring periods of high variability alternate with "stable" phases (the plateaux) when the flux is low, the spectra are hard and the timing properties of the source are similar to those of a number of black hole candidates in hard spectral state. In the plateaux the power density spectra are dominated by a low frequency quasi periodic oscillation (LFQPO) superposed onto a band limited noise continuum and accompanied by at least one harmonic. In this paper we focus on three plateaux, presenting the analysis of the power density spectra and in particular of the LFQPO and its harmonics. While plotting the LFQPO and all the harmonics together on a frequency-width plane, we found the presence of a positive trend of broadening when the frequency increases. This trend can shed light in the nature of the harmonic content of the LFQPO and challenges the usual interpretation of these timing features.