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

TL;DR

This study analyzes the timing and spectral properties of the eclipsing low-mass X-ray binary AX J1745.6-2901 using Suzaku and Chandra data, revealing orbital parameters, spectral components, and absorption features.

Contribution

It provides the first detailed spectral and timing analysis of AX J1745.6-2901 during outburst, including orbital period, spectral components, and absorption line discoveries.

Findings

Orbital period determined as 30063.76 seconds.

Detected deep flux dips prior to eclipse.

Identified narrow absorption lines of Fe and Ni near K-shell energies.

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.