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 σv = 2300⁺⁹⁰⁰₋₇₀₀ km s⁻¹. This can be larger than what was observed in previous Chandra observations (1120 ± 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 Fe XXVI or Fe XXV, with outflow velocities of −0.29c or −0.26c, respectively. The mass loss rate is M˙ ∼ 10⁻⁸M_⊙ 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.