ECLIPSE DOES NOT HIDE, BUT REVEALS: Comprehensive X-ray Reprocessing Studies in High and Low Mass X-ray Binaries with XMM-Newton

X-ray reprocessing serves as a vital diagnostic tool for gaining insights into the environments of X-ray binary systems. However, the study of X-ray reprocessing encounters challenges arising from the blending of intense primary radiation from the compact star with the reprocessed radiation from the surrounding. Eclipsing X-ray binaries offer a unique opportunity to investigate pure reprocessed X-rays, as the companion star effectively shields the intense primary X-rays. We carried out first comprehensive studies of X-ray reprocessing in most of the eclipsing High Mass X-ray Binary (HMXB) and Low Mass X-ray Binary (LMXB) systems by comparing their X-ray spectra during and outside of eclipse using XMM-Newton. We found ample diversity in the X-ray reprocessing characteristics in HMXBs, which implies significantly dynamic wind structure surrounding the compact objects in HMXBs. Significant differences observed in X-ray reprocessing characteristics in LMXBs despite all being dipping and eclipsing sources, suggest large dependencies of X-ray reprocessing on the inclination angle, scale height of the accretion disk, relative size of the accretion disk with respect to the companion, binary separation, mass ratio between the neutron star, the companion etc. Our studies revealed unexpected X-ray behaviors. For instance, (i) we observed high equivalent widths of Fe emission lines in both SgHMXBs and SFXTs during eclipse, indicating high Fe abundance, contrary to earlier findings showing low equivalent widths in SFXTs outside of eclipse. (ii) Cen X-3 showed a lower Fe Kα equivalent width during eclipse than outside, unlike other SgHMXBs. (iii) In 4U 1538-522, low-energy X-rays were not obscured during eclipse as expected. (iv) LMXBs showed a smaller out-of-eclipse to eclipse flux ratio than HMXBs, suggesting greater reprocessing despite less dense stellar winds. Overall the studies deepen our understanding of the intricate interplay between X-ray reprocessing and the diverse mechanisms within X-ray binary systems.