Relativistic Iron Emission and Disk Reflection in Galactic Microquasar XTE J1748−288

We report evidence for an Fe K-alpha fluorescence line feature and diskreflection in the Very High, High, and Low State X-ray spectra of the galacticmicroquasar XTE J1748-288 during its June~1998 outburst. Spectral analyses aremade on data gathered throughout the outburst by the Rossi X-ray TimingExplorer Proportional Counter Array. Gaussian line, relativistic disk emissionline, and ionized disk reflection models are fit to the data. In the Very HighState the line profile appears strongly redshifted, consistent with diskemission from the innermost stable orbits around a maximally rotating Kerrblack hole. In the High State the line profile is less redshifted andincreasingly prominent. The Low State line profile is very strong (~0.5 keVequivalent width) and centered at 6.7 +/- 0.10 keV; disk line emission modelfits indicate that the inner edge of the disk fluctuates between ~20 and ~100gravitational radii in this state. The disk reflection fraction is tracedthrough the outburst; reflection from an ionized disk is preferred in the VHSand HS, and reflection from a relatively neutral disk is preferred in the LS.We discuss the implications of our findings for the binary system dynamics andaccretion flow geometry in XTE J1748-288.Comment: 32 pages, 8 figures, 5 tables. ApJ accepted 8/16/0