XRISM Observations of Accretion Disk Corona in Cyg X-2

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 ${\sigma }_v=2300_{-700}^{+900}$~km~s${}^{-1}$. This can be larger than what was observed in previous Chandra observations ($1120\pm 870$~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 $\dot{M}\sim 10^{-8}{M}_{\odot }{\mathrm{yr}}^{-1}$. Our findings suggest that the ADC in Cyg X-2 has a kinematically active environment with a high degree of turbulence and kinetic energy.

10 pages, 8 figures, Accepted for publication in ApJ