Suzaku Observation of X-ray Variability in Soft State LMC X-1

TL;DR

This study analyzes Suzaku X-ray observations of the black hole binary LMC X-1 in the soft state, revealing spectral variability and the necessity of a double Compton component model to explain the data.

Contribution

It introduces a spectral model with double Compton components that better fits the observed variability and suggests a lower black hole spin compared to previous estimates.

Findings

Significant spectral evolution above 8 keV during observation.

Flux decrease over 10^4–10^5 seconds explained by changes in hard Comptonized emission.

Inner disk radius inferred to be larger, indicating a lower spin parameter.

Abstract

This paper reports the results of Suzaku observation of the spectral variation of the black hole binary LMCX-1 in the soft state. The observationwas carried out in 2009 from July 21 to 24. the obtained net count rate was $\sim$30 counts s$^{-1}$ in the 0.5--50 keV band with $\sim$10% peak-to-peak flux variation. The time-averaged X-ray spectrum cannot be described by a multi-color disk and single Compton component with its reflection, but requires additional Comptonized emissions. This double Compton component model allows a slightly larger inner radius of the multi-color disk, implying a lower spin parameter. Significant spectral evolution was observed above 8 keV along with a flux decrease on a timescale of $\sim$10$^4$--10$^5$ s. By spectral fitting, we show that this behavior is well explained by changes in the hard Comptonized emission component in contrast to the maintained disk and soft Comptonized emission.