2009ApJ...692L..80S

We observed at very high spectral resolution the prototype Z-source Cyg X-2 twice along its entire X-ray spectral variation pattern. In this preliminary analysis, we find an extended accretion disk corona (ADC) exhibiting Lyα emissions from various H-like ions, as well as emissions from He-like ions of Fe and Al, and Be-like ions of Fe. The brightest lines show a range of line broadening: H-like lines are very broad with Doppler velocities between 1100 and 2700 km/s, while some others are narrower with widths of a few hundred km/s. Line diagnostics allow us for the first time to determine coronal parameters. The line properties are consistent with a stationary, extended up to 10¹⁰ cm, dense (1x10¹⁵/cm3), and hot (log ξ ≳ 3; T ≳ 10⁶ K) ADC. We find ongoing heating of the corona along the Z-track and determine that heating luminosities change from about 0.4xL_Eddon the horizontal to about 1.4xL_Edd on the flaring branch.