A highly-ionized absorber in the X-ray binary 4U 1323-62: A new explanation for the dipping phenomenon

Abstract

Abstract.We report the detection of narrow Fe  and Fe  X-ray absorption lines at 6.68 ± 0.04 keV and 6.97 ± 0.05 keV in the persistent emission of the dipping low-mass X-ray binary 4U 1323−62 during a 2003 January XMM-Newton observation. These features are superposed on a broad emission feature centered on 6.6 +0.1 −0.2 keV. During dipping intervals the equivalent width of the Fe  feature increases while that of the Fe  feature decreases, consistent with the presence of less strongly ionized material in the line-of-sight. As observed previously, the changes in the 1.0-10 keV 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 −1 , 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) × 10 22 atoms cm −2 to (37 ± 2) × 10 22 atoms cm −2 . 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.

XMM–Newton view of a hard X-ray transient IGR J17497–2821

“…Unfortunately, we cannot verify the 1-keV excess with the RGS data. However, similar excess in the timing mode data have also been reported by several authors (Hiemstra et al 2011;Boirin et al 2005;Martocchia et al 2006;Sala et al 2008). We find that the EPIC-pn and MOS2 data show excess emission below ∼ 1.2 keV but with different shapes.…”

Multi-instrument X-ray monitoring of the January 2009 outburst from the recurrent magnetar candidate 1E 1547.0-5408

“…We note that a significant excess in the XMM-Newton PN fit residuals was detected below 1.2 keV, independent of the spectral model used. Similar residuals are rather common in the PN spectra of bright and strongly absorbed sources, suggesting that this soft excess is due to calibration issues (see, e.g., Boirin et al 2005;Sidoli et al 2005;Martocchia et al 2006). Consequently we analyzed the XMM-Newton spectrum in the energy range 1.2-10 keV only.…”

Achromatic late-time variability in thermonuclear X-ray bursts

“…The splashes usually populate a small range of orbital phases and return to the line of sight periodically, obscuring the inner (X-ray radiating) disk, resulting in dips in the lightcurve with typical durations of a few tens of seconds. The dip spectrum can be modeled by a combination of energy-dependent absorption by cold matter and energyindependent absorption by warm photoionized matter with a photo-ionization parameter of ξ = L/n e r 2 ∼ 10 2.5−3 erg s −1 cm (Boirin et al 2005;Díaz Trigo et al 2006). The dips reported here are not connected to certain orbital phases, but to certain phases in long bursts.…”