We report spectral and variability analysis of two quiescent low mass X-ray binaries ( X5 and X7 , previously detected with the ROSAT HRI ) in a Chandra ACIS-I observation of the globular cluster 47 Tuc .
X5 demonstrates sharp eclipses with an 8.666 \pm 0.01 hr period , as well as dips showing an increased N _ { H } column .
The thermal spectra of X5 and X7 are well-modeled by unmagnetized hydrogen atmospheres of hot neutron stars .
No hard power law component is required .
A possible edge or absorption feature is identified near 0.64 keV , perhaps an OV edge from a hot wind .
Spectral fits imply that X7 is significantly more massive than the canonical 1.4 { M _ { \odot } } neutron star mass , with M > 1.8 { M _ { \odot } } for a radius range of 9-14 km , while X5 ’ s spectrum is consistent with a neutron star of mass 1.4 M _ { \odot } for the same radius range .
Alternatively , if much of the X-ray luminosity is due to continuing accretion onto the neutron star surface , the feature may be the 0.87 keV rest-frame absorption complex ( O VIII & other metal lines ) intrinsic to the neutron star atmosphere , and a mass of 1.4 { M _ { \odot } } for X7 may be allowed .