The Spin of the Black Hole Microquasar XTE J1550-564 via the Continuum-Fitting and Fe-Line Methods

TL;DR

This study measures the spin of the black hole in XTE J1550-564 using two independent methods, finding consistent moderate spin values that imply the jet is mainly powered by accretion rather than black hole spin.

Contribution

First simultaneous application of continuum-fitting and Fe-line methods to measure black hole spin in XTE J1550-564, demonstrating their agreement and providing a comprehensive spin estimate.

Findings

Black hole spin estimated as a* ≈ 0.49 with uncertainties.

Spin measurement consistent across two different methods.

Jet power likely driven by accretion disc rather than black hole spin.

Abstract

We measure the spin of XTE J1550-564 in two ways: by modelling the thermal continuum spectrum of the accretion disc, and independently by modeling the broad red wing of the reflection fluorescence Fe-K line. We find that the spin measurements conducted independently using both leading methods are in agreement with one another. For the continuum-fitting analysis, we use a data sample consisting of several dozen RXTE 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 of this microquasar is powered largely by its accretion disc rather than by the spin energy of the black hole.