QPOs are more than timing features: Applying the Accretion-Ejection Instability in Super massive black-holes

TL;DR

This paper explores the application of the Accretion-Ejection Instability (AEI) model to supermassive black holes, predicting detectable spectral effects of QPOs and providing initial observational evidence supporting the model.

Contribution

It extends the AEI model from low-mass X-ray binaries to supermassive black holes and demonstrates potential spectral signatures of QPOs in these systems.

Findings

AEI causes spectral imprints in SMBH QPOs detectable with current instruments

Initial proof of concept with 2XMM J123103.2 supports AEI predictions

Spectral effects are consistent with the AEI model at 1.7 sigma significance

Abstract

Low Frequency QPOs (LFQPOs) have always been seen uniquely as a timing feature, with most models focused on reproducing only their timing behavior. Previously, the Accretion-Ejection Instability (AEI) predicted the existence of a more subtle effect on their energy spectrum. In the case of LMXB, that effect was deemed impossible to detect. While the AEI can be naturally expanded to higher-mass systems, there was no observational drive to do it until now. However the several (candidate) QPOs detected in supermassive black hole sources in the last decade, now seems the right moment to explore the applicability of the AEI model. Using our numerical observatory, we compute the different observables for a system with the AEI active and we take advantage of the longer timescale coming from the higher mass system, to see if the effect on the energy spectrum hinted at in LMXB, could become detectable. After confirming that the AEI causes an imprint of the QPO on the energy spectrum that should reach detectable levels in SMBH, we turned to observations of 2XMM J123103.2 and performed a proof of concept spectro-timing fit of the QPO pulse profile simultaneously with how its energy spectrum changes along it. While the limited 2XMM J123103.2 data showed the predicted effect at only $1.7\sigma$, it is fully consistent with the AEI model and hence worthy of further investigation in other systems.