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

TL;DR

This study uses high-resolution spectroscopy to analyze the extended accretion disk corona in Cyg X-2, revealing its composition, physical parameters, and ongoing heating processes along the Z-pattern.

Contribution

First detailed diagnostics of the coronal parameters in Cyg X-2's accretion disk corona using spectral line analysis.

Findings

Coronal density is approximately 10^15 cm^-3.

Coronal temperature exceeds 10^6 K.

Heating luminosity varies from 0.4 to 1.4 L_Edd along the Z-track.

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 exhibiting Lyman alpha emissions from various H-like ions, as well as emissions from He-like ions of Fe and Al, and Li-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 10^10 cm, dense (1x10^15 cm^-3), and hot (log xi > 3; T > 10^6 K) accretion disk corona. 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.