HEATING IN AN EXTENDED ACCRETION DISK CORONA ALONG THE Z-PATTERN IN CYG X-2

Abstract

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[superscript –1], while some others are narrower with widths of a few hundred km s[superscript –1]. 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 (1 × 10[superscript 15] cm[superscript –3]), and hot (log ξ > 3; T > 10[superscript 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[subscript Edd] on the horizontal to about 1.4 × L[subscript Edd] on the flaring branch.