Relativistic Iron Emission and Disk Reflection in Galactic Microquasar XTE J 1748 − 288

We report evidence for an Fe Kα fluorescence line feature and disk reflection in the Very High, High, and Low State X-ray spectra of the galactic microquasar XTE J1748−288 during its June 1998 outburst. Spectral analyses are made on data gathered throughout the outburst by the Rossi X-ray Timing Explorer Proportional Counter Array. Gaussian line, relativistic disk emission line, and ionized disk reflection models are fit to the data. In the Very High State the line profile appears strongly redshifted, consistent with disk emission from the innermost stable orbits around a maximally rotating Kerr black hole. In the High State the line profile is less redshifted and increasingly prominent. The Low State line profile is very strong (∼0.5 keV equivalent width) and centered at 6.7±0.10 keV; disk line emission model fits indicate that the inner edge of the disk fluctuates between ∼20 and ∼100 Rg in this state. The disk reflection fraction is traced through the outburst; reflection from an ionized disk is preferred in the VHS and 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 and accretion flow geometry in XTE J1748−288. Center for Space Research and Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139–4307; [email protected], [email protected], [email protected], [email protected], [email protected] Harvard–Smithsonian Center for Astrophysics, Harvard University, Cambridge MA 02138; [email protected] OAB Brera, Italy; [email protected] NASA MSFC, SD-50, Huntsville, AL 35812; [email protected] Chandra fellow