Distinct Fe-K Line Complexes in MAXI J1744-294 Revealed by XRISM High-Resolution Spectroscopy

TL;DR

High-resolution XRISM spectroscopy of MAXI J1744-294 uncovered complex Fe-K line features revealing distinct ionized plasma components, providing new insights into accretion disk and wind reprocessing in X-ray binaries during the soft state.

Contribution

First detailed high-resolution spectral analysis of MAXI J1744-294 revealing complex iron line structures and stratified ionized plasma components in a low-mass X-ray binary.

Findings

Detected distinct Fe XXV emission and Fe XXVI absorption lines.

Identified two ionized plasma components with different turbulent velocities.

Source is in the soft spectral state with high ionization levels.

Abstract

The newly discovered Galactic transient MAXI J1744-294 went into its first X-ray outburst in 2025. We study the spectral properties of this source in the 2-10 keV energy band during this outburst using X-ray data from the XRISM satellite for both of its Resolve and Xtend instruments, taken on March 03, 2025. High-resolution spectroscopy has revealed, for the first time, complex iron line features in this source, corresponding to distinct components of Fe XXV emission and Fe XXVI absorption lines. Such a detailed structure has not been reported in other low-mass X-ray binaries to date, prior to the XRISM era. Our analysis shows that the line complexes arise from two highly ionized plasmas with ionization rate ~ 1000 erg-cm/s with distinct turbulent velocities: one broad (~2513 km/s) from hot gas at the inner accretion disk and one narrow (~153 km/s) scattered by nearby photoionized gas. These results offer new insight into the reprocessing of continuum in stratified media, either in the accretion disk or winds, or both, for XRBs in the soft state. The data are well described by models with spin, mass of the black hole, and accretion disk inclination 0.63-0.70, 5.7-10.1 Solar masses, and 19-24 degrees. The fitted spectral model parameters suggest that the source is in the soft spectral state. The source is situated in a crowded field near the Galactic center, resulting in a large hydrogen column density.