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 Heα 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 multi-velocity 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 Heα complex, focusing on the forbidden to resonance line ratio under the influence of continuum pumping and optical depth effects.