The XRISM/Resolve view of the Fe K region of Cyg X-3

TL;DR

This study uses high-resolution XRISM spectroscopy to analyze the complex ionized gas dynamics in Cyg X-3, revealing multiple velocity components and detailed line profiles that improve understanding of the system's wind structure.

Contribution

First high-resolution spectral analysis of Cyg X-3 with XRISM, disentangling absorption and emission components and measuring their velocities across the binary orbit.

Findings

Detection of multiple ionization and kinematic components.

Higher velocity amplitude in emission lines compared to absorption.

Identification of a wind structure with smooth and turbulent components.

Abstract

The X-ray binary system Cygnus X-3 (4U 2030+40, V1521 Cyg) is luminous but enigmatic owing to the high intervening absorption. High-resolution X-ray spectroscopy uniquely probes the dynamics of the photoionized gas in the system. In this paper we report on an observation of Cyg X-3 with the XRISM/Resolve spectrometer which provides unprecedented spectral resolution and sensitivity in the 2-10 keV band. We detect multiple kinematic and ionization components in absorption and emission, whose superposition leads to complex line profiles, including strong P-Cygni profiles on resonance lines. The prominent Fe XXV He$\alpha$ and Fe XXVI Ly$\alpha$ emission complexes are clearly resolved into their characteristic fine structure transitions. Self-consistent photoionization modeling allows us to disentangle the absorption and emission components and measure the Doppler velocity of these components as a function of binary orbital phase. We find a significantly higher velocity amplitude for the emission lines than for the absorption lines. The absorption lines generally appear blueshifted by ${\sim}-500$-$600$km s$^{-1}$. We show that the wind decomposes naturally into a relatively smooth and large scale component, perhaps originating with the background wind itself, plus a turbulent more dense structure located close to the compact object in its orbit.