arXiv:2205.04475 [astro-ph.HE]AbstractReferencesReviewsResources Classifications Subjects Themes Keywords x-ray binary 4u, orbital period challenges, ultra-compact nature, ultra-compact x-ray binary candidate 4u, low optical-to-x-ray flux ratio Tags Journal Information Publisher Journal Year Month Volume Number Pages DOI URL Miscellaneous Typesetting Pages Language License Submit Reset