Timing and Spectral Study of AXJ1745.6$-$2901 with Suzaku

Abstract

The eclipsing low-mass X-ray binary AX J1745.6$-$2901 was observed with Suzaku in its outburst phase. Combining the Chandra observation made 1.5 month earlier than Suzaku, we determined the orbital period to be 30063.76$\pm$0.14 s. We found deep flux dips prior to the eclipse phase of the orbit. The X-ray spectrum of the persistent phase is described by a combination of a direct and a scattered-in components by dust emission. During the eclipse, the X-ray spectrum becomes only the dust scattering (scattered-in) component. The optical depth of the dust scattering is $\sim$ 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 $\sim$ 7.1 keV in the deep dip spectrum indicates that the major portion of Fe in the absorber is neutral, or in a 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 $\sim$ 10$^{3}$kms$^{-1}$.