The spin of the black hole microquasar XTE J1550−564 via the continuum-fitting and Fe-line methods

Abstract

We measure the spin of XTE J1550-564 using the two leading methods: (i) modelling the thermal continuum spectrum of the accretion disc; and (ii) modelling the broad red wing of the reflection fluorescence Fe K line. We find that these two independent measurements of spin are in agreement. For the continuum-fitting analysis, we use a data sample consisting of several dozen Rossi X-ray Timing Explorer spectra, and for the Fe K analysis, we use a pair of ASCA spectra from a single epoch. Our spin estimate for the black hole primary using the continuum-fitting method is -0.11 < a * < 0.71 (90 per cent confidence), with a most likely spin of a * = 0.34. In obtaining this result, we have thoroughly explored the dependence of the spin value on a wide range of model-dependent systematic errors and observational errors; our precision is limited by uncertainties in the distance and orbital inclination of the system. For the Fe-line method, our estimate of spin is a * = 0.55 +0.15 -0.22 . Combining these results, we conclude that the spin of this black hole is moderate, a * = 0.49 +0.13 -0.20 , which suggests that the jet activity of this microquasar is powered largely by its accretion disc rather than by the spin energy of the black hole.