Broad-band mHz QPOs and spectral study of LMC X-4 with AstroSat

Abstract

ABSTRACT We report the results of broad-band timing and spectral analysis of data from an AstroSat observation of the high-mass X-ray binary LMC X-4. The Large Area X-ray Proportional Counter (LAXPC) and Soft X-ray Telescope (SXT) instruments onboard the AstroSatobserved the source in 2016 August. A complete X-ray eclipse was detected with the LAXPC. The 3–40 keV power density spectrum showed the presence of coherent pulsations along with a ∼26 mHz quasi-periodic oscillation feature. The spectral properties of LMC X-4 were derived from a joint analysis of the SXT and LAXPC spectral data. The 0.5–25 keV persistent spectrum comprised of an absorbed high-energy cut-off power law with photon index of Γ ∼ 0.8 and cut-off at ∼16 keV, a soft thermal component with kTBB ∼ 0.14 keV, and Gaussian components corresponding to Fe Kα, Ne ix, and Ne x emission lines. Assuming a source distance of 50 kpc, we determined 0.5–25 keV luminosity to be ∼2 × 1038 erg s−1.