**Publication date:** Feb 2013

**Abstract:**

The black hole mass and spin estimates assuming various specific models

of the 3 : 2 high frequency quasi-periodic oscillations (HF QPOs) have

been carried out in Török et al. (2005, 2011). Here we briefly

summarize some current points. Spectral fitting of the spin a ≡

cJ/GM 2 in the microquasar GRS 1915 + 105 reveals that this

system can contain a near extreme rotating black hole (e.g., McClintock

et al., 2011). Confirming the high value of the spin would have

significant consequences for the theory of the HF QPOs. The estimate of

a > 0.9 is almost inconsistent with the relativistic precession (RP),

tidal disruption (TD), and the warped disc (WD) model. The epicyclic

resonance (Ep) and discoseismic models assuming the c- and g- modes are

instead favoured. However, consideration of all three microquasars that

display the 3 : 2 HF QPOs leads to a serious puzzle because the

differences in the individual spins, such as a = 0.9 compared to a =

0.7, represent a generic problem almost for any unified orbital 3:2 QPO

model.

**Authors:**

Kotrlová, Andrea; Török, Gabriel; Šrámková, Eva; Stuchlík, Zdeněk;