Timing and spectral studies of Cen X-3 in multiple luminosity states using AstroSat

Abstract

We present the results of timing and spectral analysis of the high-mass X-ray binary pulsar, Cen X-3, with the help of observations carried out using the Large Area X-ray Proportional Counter onboard AstroSat. As part of our analysis, we sampled the source properties during four different observation epochs covering two widely different intensity states. We obtain a timing solution and report precise measurements of the spin and orbital parameters corresponding to these observational epochs. The pulse profiles during the two intensity states reveal dramatically varying shapes within a time span of 1 month. We report the detection of one of the lowest measured frequencies of quasi-periodic oscillations at 0.026 ± 0.001 Hz for Cen X-3 during its low-intensity state. We also find correlated periodic and aperiodic noise components in the power density spectra. We further carried out a phase-averaged and a pulse phase-resolved spectral study, where we find that the best-fitting continuum spectrum is well described by an absorbed Comptonization model along with a blackbody. Cen X-3 exhibited the presence of the ∼28 keV cyclotron resonant scattering feature absorption line and a ∼6.6 keV Fe emission line in both the intensity states. Significant variations in the line-forming regions and mode of accretion for Cen X-3 within time spans of a month make Cen X-3 a highly dynamic persistent binary.