High Resolution X-Ray Spectroscopy Of Cygnus X-3 With Chandra

We analyze the Fe K spectrum of the high mass X-ray binary Cygnus X-3, using the highest resolution data available, obtained with the High Energy Transmission Grating Spectrometer on the Chandra X-ray Observatory in third spectral order. The increased energy resolution of the third order enables us to fully resolve the Fe XXV He-alpha complex, the Fe XXVI Lyα lines, and detect narrow radiative recombination continuum features from highly ionized Fe. This is the first resolved Fe XXV spectrum from a source driven by photoionization and radiative transfer, and we identify and describe unique features of the Fe XXV spectrum that are characteristic of these conditions. A preliminary analysis of the Fe XXV recombination continuum at 8.828 keV suggests a maximum gas temperature (in the highest Fe ionization zone) of the order of the instrument resolution, or 30 eV. We identify a P Cygni profile in the Fe XXV w line. Finally, we estimate the Doppler shifts of individual lines in the Fe XXVI and Fe XXV complexes. Using the fact that we do not detect significant orbital Doppler shifts in the emission lines from the highest ionization zones of the companion stellar wind closest to the compact object, we infer a lower limit to the compact object mass of the order of the mass of the Wolf-Rayet companion star.