Detection of a pulsating soft component in the X-ray pulsar XTE J0111.2-7317

Abstract

The newly discovered transient X-ray pulsar XTE J0111.2-7317 was observed with ASCA in its bright phase. The pulsation was found to be nearly sinusoidal with some energy dependence (17%, 21% and 30% pulse fractions in 0.5-1.0, 1.0-2.0 and 2.0-10.0 keV bands respectively). In addition to a hard power-law component in the 2-10 keV band, the energy spectrum has a soft excess in the 0.5-2 keV band. Thermal models for the soft excess require very large emission zone for the soft component and can be ruled out based on the pulsations observed at low energies. The low energy excess can however be accommodated if the incident spectrum is modeled as an inversely broken power-law with line of sight absorption. We have also detected an iron Kα emission line with equivalent width of 50+/-14 eV