A Broad Iron Line in LMC X-1

TL;DR

This study uses deep Suzaku and RXTE observations to analyze the relativistic reflection features in LMC X-1, constraining the black hole's spin and revealing wind-related reprocessing phenomena.

Contribution

It provides the first detailed modeling of relativistic reflection features in LMC X-1 and constrains the black hole's spin with systematic uncertainty considerations.

Findings

Black hole spin constrained to a* ≈ 0.97 with uncertainties

Detection of strong relativistic reflection features

Evidence for wind reprocessing in the companion's wind

Abstract

We present results from a deep Suzaku observation of the black hole in LMC X-1, supplemented by coincident monitoring with RXTE. We identify broad relativistic reflection features in a soft disc-dominated spectrum. A strong and variable power-law component of emission is present which we use to demonstrate that enhanced Comptonisation strengthens disc reflection. We constrain the spin parameter of the black hole by modelling LMC X-1's broad reflection features. For our primary and most comprehensive spectral model, we obtain a high value for the spin: a* = 0.97(+0.01,-0.13) (68 per cent confidence). However, by additionally considering two alternate models as a measure of our systematic uncertainty, we obtain a broader constraint: a* = 0.97(+0.02,-0.25). Both of these spin values are entirely consistent with a previous estimate of spin obtained using the continuum-fitting method. At 99 per cent confidence, the reflection features require a* > 0.2. In addition to modelling the relativistically broadened reflection, we also model a sharp and prominent reflection component that provides strong evidence for substantial reprocessing in the wind of the massive companion. We infer that this wind sustains the ionisation cone surrounding the binary system; this hypothesis naturally produces appropriate and consistent mass, time, and length scales for the cone structure.