# Post-flare Formation of the Accretion Stream and a Dip in Pulse Profiles of LMC X-4

## TL;DR

This study examines how large X-ray flares affect the pulse profiles of LMC X-4, revealing a temporary phase offset and the formation of an accretion stream that influences the pulsar's emission structure.

## Contribution

It provides new insights into the post-flare evolution of accretion columns and pulse profile modifications in LMC X-4 using combined XMM-Newton and RXTE data.

## Key findings

- Pulse profiles show significant phase offsets during flares.
- It takes 2000-4000 seconds for the accretion column to normalize.
- The soft spectral component pulsates with a different phase from the power-law.

## 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 10^5 seconds after the flares, it was found that it takes about 2000-4000 seconds 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.