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 the 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 ultrafast outflow. The ADC component has at least two distinct regions. The Fe–K emission lines are remarkably broad, with a velocity dispersion of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>σ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>v</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>230</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>700</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>900</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> 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 −0.29 c or −0.26 c , respectively. The mass loss rate is <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> <mml:mo>∼</mml:mo> <mml:mn>1</mml:mn> <mml:msup> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>8</mml:mn> </mml:mrow> </mml:msup> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">yr</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> . Our findings suggest that the ADC in Cyg X-2 has a kinematically active environment with a high degree of turbulence and kinetic energy.