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

James F Steiner,Ronald A Remillard,Jeffrey E Mcclintock,Manuel A P Torres,Ramesh Narayan,Lijun Gou,Andrew C Fabian,Rubens C Reis,Jerome A Orosz

doi:10.1111/j.1365-2966.2011.19089.x

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.

Highlights

During its principal 1998–1999 outburst cycle, the bright Xray transient XTE J1550–564 produced one of the most remarkable flare events ever observed for a black hole binary
The Spin of the Black Hole in XTE J1550–564 3 considered in their study, and additional data; unlike this exploratory and preliminary study of eight blackhole systems, we fixedly focus on J1550 and so are able to refine and improve upon their work
In selecting our data and for determining the spin, we employ a variant of the principal model that we used in our earlier study of J1550 and H1743–322: crabcor×tbabs×smedge(simpl⊗kerrbb2)

Summary

Introduction

During its principal 1998–1999 outburst cycle, the bright Xray transient XTE J1550–564 produced one of the most remarkable flare events ever observed for a black hole binary. For ≈ 1 day, the source intensity rose fourfold relative to neighbouring plateau values, reaching 6.8 Crab. The flux in the dominant power-law component rose by the same factor, and just as quickly its intensity declined (Sobczak et al 2000; McClintock et al 2009). AU-scale superluminal radio jets were observed (Hannikainen et al 2009). Their separation angle (∼ 255 mas) and relative velocity (∼ 65 mas d−1) links the birth of these jets to the impulsive X-ray flare.

Results

Discussion

Conclusion