XRISM Observations of Accretion Disk Corona in Cyg X-2

TL;DR

This paper presents high-resolution XRISM X-ray spectra of Cyg X-2, revealing broad Fe-K emission lines, a potential ultra-fast outflow, and complex accretion disk corona dynamics, advancing understanding of accretion processes in neutron star systems.

Contribution

First detailed high-resolution X-ray spectral analysis of Cyg X-2's accretion disk corona, identifying broad Fe-K lines and potential ultra-fast outflows.

Findings

Broad Fe-K emission lines with high velocity dispersion.

Possible detection of ultra-fast outflow at ~0.27c.

Active, turbulent environment in the accretion disk corona.

Abstract

We present the high-resolution X-ray spectrum of the Z-source Cygnus X-2, obtained with X-Ray Imaging and Spectroscopy Mission (XRISM). The observations have enabled a precise characterization of the Fe-K emission lines from the accretion disk corona (ADC) and a possible detection of an ultra-fast outflow (UFO). The ADC component has at least two distinct regions. The Fe-K emission lines are remarkably broad, with a velocity dispersion of $\sigma_v=2300^{+900}_{-700}$~km~s$^{-1}$. This can be larger than what was observed in previous Chandra observations ($1120\pm870$~km~s$^{-1}$) and recent XRISM observations of the similar Z-source GX 340+0 (360--800~km~s$^{-1}$). Furthermore, we marginally detect a blueshifted absorption feature, which we identify as either \ion{Fe}{26} or \ion{Fe}{25}, with outflow velocities of $-0.29c$ or $-0.26c$, respectively. The mass loss rate is $\dot{M}\sim10^{-8}M_\odot\,\mathrm{yr}^{-1}$. Our findings suggest that the ADC in Cyg X-2 has a kinematically active environment with a high degree of turbulence and kinetic energy.