Heating in an Extended Accretion Disk Corona Along the Z-Pattern in Cyg X-2

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 −1 , while some others are narrower with widths of a few hundred km s −1 . Line diagnostics allow us for the first time to determine coronal parameters. The line properties are consistent with a stationary, extended up to 10 10 cm, dense (1 × 10 15 cm −3 ), and hot (log ξ ≳ 3; T ≳ 10 6 K) ADC. We find ongoing heating of the corona along the Z-track and determine that heating luminosities change from about 0.4 × L Edd on the horizontal to about 1.4 × L Edd on the flaring branch.