Confronting the models of 3:2 quasiperiodic oscillations with the rapid spin of the microquasar GRS 1915+105

TL;DR

This paper examines how different models of high-frequency quasiperiodic oscillations (HF QPOs) in microquasars align with the high spin estimates of GRS 1915+105, highlighting which models are consistent with near-extremal spins.

Contribution

It evaluates the compatibility of various HF QPO models with high spin estimates of GRS 1915+105 and other microquasars, emphasizing the need for non-geodesic corrections.

Findings

Hot-spot and warped disc resonance models are inconsistent with a>0.9.

Epicyclic resonance and discoseismic models are favored.

Large non-geodesic corrections are needed to unify QPO explanations across microquasars.

Abstract

Spectral fitting of the spin a in the microquasar GRS 1915+105 estimate values higher than a=0.98. However, there are certain doubts about this (nearly) extremal number. Confirming a high value of a>0.9 would have significant concequences for the theory of high-frequency quasiperiodic oscillations (HF QPOs). Here we discuss its possible implications assuming several commonly used orbital models of 3:2 HF QPOs. We show that the estimate of a>0.9 is almost inconsistent with two hot-spot (relativistic precession and tidal disruption) models and the warped disc resonance model. In contrast, we demonstrate that the epicyclic resonance and discoseismic models assuming the c- and g- modes are favoured. We extend our discussion to another two microquasars that display the 3:2 HF QPOs. The frequencies of these QPOs scale roughly inversely to the microquasar masses, and the differences in the individual spins, such as a=0.9 compared to a=0.7, represent a generic problem for most of the discussed geodesic 3:2 QPO models. To explain the observations of all the three microquasars by one unique mechanism, the models would have to accommodate very large non-geodesic corrections.