  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.
