High-Frequency Quasi-Periodic Oscillations from GRS 1915+105

TL;DR

This study systematically analyzed RXTE data of GRS 1915+105, detecting high-frequency quasi-periodic oscillations around 67 Hz, primarily during a specific spectral state, with implications for understanding accretion processes in black-hole binaries.

Contribution

First comprehensive timing analysis of GRS 1915+105's HFQPOs, identifying their frequency, spectral state dependence, and spectral properties, advancing understanding of black-hole accretion phenomena.

Findings

Detected 51 HFQPO peaks with centroid frequencies around 67 Hz.

HFQPOs are confined to a specific spectral state (state B).

RMS spectrum of HFQPOs remains hard up to 40 keV.

Abstract

We report the results of a systematic timing analysis of all archival Rossi X-Ray Timing Explorer (RXTE) observations of the bright black-hole binary GRS 1915+105 in order to detect high-frequency quasi-periodic oscillations (HFQPO). We produced power-density spectra in two energy bands and limited the analysis to the frequency range 30-1000 Hz. We found 51 peaks with a single trial significance larger than 3 sigma. As all but three have centroid frequencies that are distributed between 63 and 71 Hz, we consider most of them significant regardless of the number of trials involved. The average centroid frequency and FWHM are 67.3 +/- 2.0 Hz and 4.4 +/- 2.4 Hz respectively. Their fractional rms varies between 0.4% and 2% (total band detections) and between 0.5% and 3% (hard ban detections). As GRS 1915+105 shows large variability on time scales longer than 1s, we analysed the data in 16s intervals and found that the detections are limited to a specific region in the colour-colour diagram, corresponding to state B of the source, when the energy spectrum is dominated by a bright accretion disk component. However, the rms spectrum of the HFQPO is very hard and does not show a flattening up to 40 keV, where the fractional rms reaches 11%. We discuss our findings in terms of current proposed models and compare them with the results on other black-hole binaries and neutron-star binaries.