2005A&A...436..195B

We report the detection of narrow FeXXV and FeXXVI X-ray absorption lines at 6.68±0.04keV and 6.97±0.05keV in the persistent emission of the dipping low-mass X-ray binary 4U1323-62 during a 2003 January XMM-Newton observation. These features are superposed on a broad emission feature centered on 6.6^+0.1_–0.2keV. During dipping intervals the equivalent width of the FeXXV feature increases while that of the FeXXVI feature decreases, consistent with the presence of less strongly ionized material in the line-of-sight. As observed previously, the changes in the 1.0-10keV spectrum during dips are inconsistent with a simple increase in absorption by cool material. However, the changes in both the absorption features and the continuum can be modeled by variations in the properties of an ionized absorber. No partial covering of any component of the spectrum, and hence no extended corona, are required. From persistent to deep dipping, the photo-ionization parameter, ξ, expressed in erg cm/s, decreases from log(ξ) of 3.9±0.1 to log(ξ) of 3.13±0.07, while the equivalent hydrogen column density of the ionized absorber increases from (3.8±0.4)x10²²atoms/cm² to (37±2)x10²²atoms/cm². Since highly-ionized absorption features are seen from many other dip sources, this mechanism may also explain the overall changes in X-ray spectrum observed during dipping intervals from these systems.