ECLIPSE DOES NOT HIDE, BUT REVEALS: Comprehensive X-ray Reprocessing Study in High

and Low Mass X-ray Binaries with XMM-Newton

Nafisa Aftab

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 a comprehensive study of X-ray reprocessing in several 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 EPIC pn.

We found ample diversity in the X-ray reprocessing characteristics in HMXBs, which implies significantly dynamic wind structure surrounding the compact object in HMXBs. The X-ray reprocessing characteristics observed in LMXBs indicate large dependencies of X-ray reprocessing on the scale height of the accretion disk, relative size of the disk compared to the companion and some other unknown factors. In HMXBs, the continuum spectrum component is significantly reduced during eclipse, while the count rate of iron emission lines remains relatively stable. This indicates the presence of a large emission region for iron lines, potentially comparable to the size of the companion star. Whereas, this line is hardly seen in the eclipse spectra of the LMXBs. In LMXBs, we observed a smaller out-of-eclipse to eclipse flux ratio compared to HMXBs, indicating greater X-ray reprocessing despite having a less dense and less extended stellar wind from the companion star.

Overall, our studies reveal different unique features in each binary system even though they belong to the same class. The study deepens our understanding of the intricate interplay between X-ray reprocessing and the diverse mechanisms within X-ray binary systems.