The Discovery of 3.8 Hour Periodic Intensity Dips and Eclipses from the Transient Low-Mass X-Ray Binary EXO 0748-676

Abstract

Using the EXOSAT Observatory the authors have discovered a new transient X-ray burst source EXO 0748-676 that shows 8.3 minute duration X-ray eclipses that recur with a period of 3.82 hr. If the companion star is on the main sequence, the eclipse duration gives a companion mass of 0.45 M_sun; and a system inclination of 75°. Irregular intensity dips that involve up to an 80% reduction in 2 - 10 keV intensity are observed at orbital phases between ≡0.8 - 0.2. The intensity dips are most likely due to obscuration of the central X-ray source by a thickened region at the outer edge of the accretion disk that is caused by its interaction with the inflowing gas stream.