AstroSat view of LMC X-2: evolution of broad-band X-ray spectral properties along a complete Z-track

In this paper, we report the first results of the extragalactic Z-source Large Magellanic Cloud (LMC) X-2 obtained using the similar to 140 ks observations with Large Area X-ray Proportional Counter (LAXPC) and Soft X-ray Telescope (SXT) onboard AstroSat. The Hardness-Intensity Diagram created with the LAXPC data revealed a complete Z-pattern of the source, showing all the three branches. We studied the evolution of the broad-band X-ray spectra in the energy range of 0.5-20.0 keV along the Z-track, a first such study of this source. The X-ray spectra of the different parts of the Z-pattern were well described by an absorbed Comptonized component. An absence of the accretion disc component suggests that the disc is most probably obscured by a Comptonized region. The best fit electron temperature (kT(e)) was found to be in the range of 1.7-2.1 keV and optical depth (tau) was found to be in the range of 13.2-17.5. The optical depth (tau) increased as the source moved from the normal/flaring branch (NB/FB) vertex to the upper part of the FB, suggesting a possible outflow triggered by a strong radiation pressure. The power density spectra (PDS) of HB and NB could be fitted with a pure power law of index alpha similar to 1.68 and 0.83, respectively. We also found a weak evidence of quasi-periodic oscillation (2.8s) in the FB. The intrinsic luminosity of the source varied between (1.03-1.79) x 10(38) erg s(-1). We discuss our results by comparing with other Z-sources and the previous observations of LMC X-2.