Abstract:
We present the results obtained from detailed spectral and timing studies of extragalactic black hole X-ray binaries LMC X–1
and LMC X–3, using simultaneous observations with Nuclear Spectroscopic Telescope Array (NuSTAR) and Neil Gehrels Swift
observatories. The combined spectra in the 0.5–30 keV energy range, obtained between 2014 and 2019, are investigated for
both sources. We do not find any noticeable variability in 0.5–30 keV light curves, with 0.1–10 Hz fractional rms estimated to
be <2 per cent. No evidence of quasi-periodic oscillations is found in the power density spectra. The sources are found to be
in the high soft state during the observations with disc temperature Tin ∼ 1 keV, photon index, > 2.5 and thermal emission
fraction, fdisc > 80 per cent. An Fe Kα emission line is detected in the spectra of LMC X–1, though no such feature is observed
in the spectra of LMC X–3. From the spectral modelling, the spins of the black holes in LMC X–1 and LMC X–3 are estimated
to be in the range of 0.92–0.95 and 0.19−0.29, respectively. The accretion efficiency is found to be, η ∼ 0.13 and η ∼ 0.04 for
LMC X–1 and LMC X–3, respectively.
