XRISM Reveals Complex Ionization and Velocity Structures in the GX 340+0 X-Ray Binary

Abstract We present the first high-resolution XRISM spectrum of the neutron star low-mass X-ray binary GX 340+0, revealing unprecedented detail in its emission and absorption features. The spectrum reveals a rich and complex Fe xxv He α line profile and a P Cygni profile from Ca xx . We use the state-of-the-art spectral synthesis code Cloudy to model the emission and absorption features in detail. Our analysis reveals multi-ionization and multivelocity structures, where the combination of broad (∼800 km s −1 ) and narrow (∼360 km s −1 ) line components, along with rest-frame and blueshifted emission and absorption lines, accounts for the observed line profile complexity. We identify a modest ∼2735 km s −1 accretion disk wind exhibiting both absorption and emission features. We also detect a relativistic reflection feature in the spectrum, which we model using relxillNS , specifically designed to characterize X-ray reprocessing in accretion disks around neutron stars. Furthermore, we examine the detailed physics of the Fe xxv He α complex, focusing on the forbidden-to-resonance line ratio under the influence of continuum pumping and optical depth effects.