2012ApJ...753....2G

We report on Chandra X-ray Observatory (Chandra) High Energy Transmission Grating spectra of the dipping low-mass X-ray binary 1A 1744-361 during its 2008 July outburst. We find that its persistent emission is well modeled by a blackbody (kT ∼ 1.0 keV) plus power law (Γ ∼ 1.7) with an absorption edge. In the residuals of the combined spectrum, we find a significant absorption line at 6.961±0.002 keV, consistent with the Fe XXVI (hydrogen-like Fe) 2-1 transition. We place an upper limit on the velocity of a redshifted flow of v < 221 km/s. We find an equivalent width for the line of 27⁺²_- 3_eV, from which we determine a column density of (7±1)x10¹⁷/cm2 via a curve-of-growth analysis. Using XSTAR simulations, we place a lower limit on the ionization parameter of >10^3.6 erg cm/s. We discuss what implications the feature has on the system and its geometry. We also present Rossi X-ray Timing Explorer data accumulated during this latest outburst and, via an updated color-color diagram, clearly show that 1A 1744-361 is an "atoll" source.