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We present the spectroscopy of the neutron star low-mass X-ray binary 4U1636-53 using six simultaneous XMM-Newton and Rossi X-ray Timing Explorerobservations. We applied different self-consistent reflection models to explorethe features when the disk is illuminated by either the corona or the neutronstar surface. We found that the spectra could be well fitted by these two typesof models, with the derived emissivity index below a typical value of 3. Therelative low emissivity can be explained if the neutron star and the corona,working together as an extended illuminator, simultaneously illuminate andionize the disk. Additionally, the derived ionization parameter in the lamppostgeometry is larger than the theoretical prediction. This inconsistency likelysuggests that the corona does not emit isotropically in a realistic context.Furthermore, we also found that there is a possible trend between the height ofthe corona and the normalization of the disk emission. This could be understoodeither as a variation in the reflected radiation pressure or in the context ofa jet base. Finally, we found that the disk is less ionized if it isilluminated by the neutron star, indicating that the illuminating source hassignificant influence on the physical properties of the disk.

Investigation into the reflection properties of the neutron star low-mass X-ray binary 4U 1636-53