The NuSTAR View of a QPO Evolution of GRS 1915+105

TL;DR

This study analyzes NuSTAR observations of GRS 1915+105, revealing a strong type-C QPO whose frequency correlates with flux and spectral changes, suggesting inward disk motion as a possible cause.

Contribution

First detailed timing analysis of GRS 1915+105 with NuSTAR linking QPO frequency changes to disk dynamics.

Findings

QPO frequency correlates with count rate and spectral softening.

Sudden increase in QPO frequency associated with flux rise.

Reflection component has minimal impact on QPO frequency.

Abstract

We report a timing analysis of the black hole binary GRS 1915+105 with the NuSTAR observatory. A strong type-C QPO below 2 Hz appears in the power density spectrum during the whole observation, whose frequency is correlated with the 3-25 keV count rate. The QPO shows a sudden increase in frequency along with an increase in flux and a softening of the spectrum. We discuss the possible origin of the QPO and the reasons that lead to the QPO frequency variation. It is suggested that the reflection component has little influence on QPO frequency and the increase in QPO frequency could be associated with the inward motion of the outer part of the disk.