Timing and Spectral Study of AX J1745.6-2901 with Suzaku

Abstract

The eclipsing low-mass X-ray binary AX J1745.6-2901 was observed with Suzaku in its outburst phase. Combining the Chandra observation made 1.5 month earlier than Suzaku, we determined the orbital period to be 30063.76+/-0.14 s. We found deep flux dips prior to the eclipse phase of orbit. The X-ray spectrum of the persistent phase is described with a combination of a direct and a scattered-in by dust emissions. During the eclipse, the X-ray spectrum becomes only the dust scattering (scattered-in) component. The optical depth of the dust-scattering is ~10.5 at 1 keV. The direct component is composed of a blackbody likely from the neutron star surface and a disk-blackbody. No power-law component is found in the hard energy band up to 30 keV. A clear edge at ~7.1 keV in the deep dip spectrum indicates that the major portion of Fe in the absorber is neutral or at low ionization state. We discovered four narrow absorption lines near the K-shell transition energies of Fe XXV, Fe XXVI, and Ni XXVII. The absorption line features are well explained by the solar abundance gas in a bulk motion of ~10^3 km/s.