Post-flare formation of the accretion stream and a dip in pulse profiles of LMC X-4

Abstract

We report here a pulse profile evolution study of an accreting X-ray pulsar LMC X–4 during and after the large X-ray flares using data from the two observatories XMM-Newton and RXTE. During the flares, the pulse profiles were found to have a significant phase offset in the range of 0.2–0.5 compared to the pulse profiles immediately before or after the flare. Investigating the pulse profiles for about 105 s after the flares, it was found that it takes about 2000–4000 s for the modified accretion column to return to its normal structure and formation of an accretion stream that causes a dip in the pulse profile of LMC X–4. We have also carried out pulse phase resolved spectroscopy of LMC X–4 in narrow phase bins using data from EPIC-pn and spectroscopically confirmed the pulsating nature of the soft spectral component, having a pulse fraction and phase different from that of the power-law component.