AN Fe XXIV ABSORPTION LINE IN THE PERSISTENT SPECTRUM OF THE DIPPING LOW-MASS X-RAY BINARY 1A 1744-361

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 similar to 1.0 keV) plus power law (Gamma similar to 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 flowof nu < 221 km s(-1). We find an equivalent width for the line of 27(-3)(+2) eV, from which we determine a column density of (7 +/- 1) x 10(17) cm(-2) 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(-1). 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.