Publication date: Jul 2016
Abstract:
Estimates of the black hole mass M and the dimensionless spin a in the
microquasar GRO J1655-40 implied by strong gravity effects related to
the timing and spectral measurements are controversial, if the mass
restriction determined by the dynamics related to independent optical
measurements, M opt = (5.4 ± 0.3) M ☉, is applied.
The timing measurements of twin high-frequency (HF) quasiperiodic
oscillations (QPOs) with the frequency ratio 3:2 and the simultaneously
observed low-frequency (LF) QPO imply spin in the range ain
(0.27{–}0.29) if models based on the frequencies of geodesic epicyclic
motion are used to fit the timing measurements, and the correlated
creation of the twin HF QPOs and the LF QPO at a common radius is
assumed. On the other hand, the spectral continuum method implies ain
(0.65{–}0.75), and the Fe-line-profile method implies ain
(0.94{–}0.98). This controversy can be cured if we abandon the
assumption of the occurrence of the twin HF QPOs and the simultaneously
observed LF QPO at a common radius. We demonstrate that the epicyclic
resonance model of the twin HF QPOs is able to predict the spin in
agreement with the Fe-profile method, but no model based on the geodesic
epicyclic frequencies can be in agreement with the spectral continuum
method. We also show that the non-geodesic string loop oscillation model
of twin HF QPOs predicts spin a > 0.3 under the optical measurement
limit on the black hole mass, which is in agreement with both the
spectral continuum and Fe-profile methods.
Authors:
Stuchlík, Z.; Kološ, M.;