Black hole spin measurements through the relativistic precession model: XTE J1550-564

Abstract

We present a systematic analysis of the complete set of observations of the black hole (BH) binary XTE J1550-564 obtained by the Rossi X-ray Timing Explorer. We study the fast time variability properties of the source and determine the spin of the black hole through the relativistic precession model. Similarly to what is observed in the BH binary GRO J1655-40, the frequencies of the QPOs and broad band noise components match the general relativistic frequencies of particle motion close to the compact object predicted by the relativistic precession model. The combination of two simultaneously observed quasi-periodic oscillation (QPO) frequencies together with the dynamical BH mass from optical/infrared observations yields a spin equal to a = 0.34 +/-0.01, consistent with previous determinations from X-ray spectroscopy. Based on the derived BH parameters, the low frequency QPO emission radii vary from ∼ 30 gravitational radii (R g ) to the innermost stable orbit for this spin (∼ 5 R g ), where they sharply disappear as observed for the case of GRO J1655-40.

Testing the nature of the black hole candidate in GRO J1655-40 with the relativistic precession model

“…The authors of Ref. [50] find that the inferred value of M is in agreement with the value obtained by dynamical methods in Ref. [51].…”

“…The result is an allowed region on the spin-deformation parameter plane, just like the authors of Ref. [50] find an allowed region on the mass-spin plane. The strong correlation between the spin and possible deviations from the Kerr solution found with other approaches is present even here, but the size of the allowed region is much smaller, supporting the idea that, if properly understood, QPOs can be a very powerful tool to probe the spacetime geometry around BH candidates.…”

“…In support of the relativistic precession model, the authors of Ref. [50] show also that the X-ray data of GRO J1655-40 with two simultaneous QPOs can be nicely interpreted as two of the three frequencies generated at radii r larger than the one found in the data with three frequencies. However, their spin measurement is not consistent with the one obtained from the continuum-fitting method in Ref.…”

“…Very recently, some authors have pointed out that the X-ray data of GRO J1655-40 nicely fit in the relativistic precession model [50]. The key-point is that this source is the only one for which three simultaneous QPOs have been observed.…”

“…[50] to test the spacetime geometry around the BH candidate in GRO J1655-40. For this purpose, it is convenient to consider a metric more general than the Kerr one, with one (or more) deformation parameter(s).…”