XRISM/Resolve reveals the complex iron structure of NGC 7213: Evidence for radial stratification between inner disk and broad-line region

TL;DR

This study uses high-resolution X-ray spectroscopy to reveal a radially stratified structure in NGC 7213, showing different emission regions from the inner disk to the broad-line region, indicating an intermediate accretion state.

Contribution

First high-resolution X-ray spectrum of NGC 7213 revealing detailed iron line structures and their spatial origins, demonstrating a radially stratified emission region.

Findings

Neutral Fe Kα split into narrow and disk-like components

Detection of broadened Fe XXV and Fe XXVI lines bridging disk and BLR

Evidence for a low-covering-fraction, Compton-thin torus

Abstract

We present the first high-resolution X-ray spectrum of NGC 7213 obtained with XRISM/Resolve, supported by simultaneous XMM-Newton, NuSTAR, and SOAR optical data. The XRISM spectrum resolves the neutral Fe\,K$\alpha$ into two components: a narrow core ($\rm FWHM = 650_{-220}^{+240}\,\rm km\,s^{-1}$) consistent with emission at the dust sublimation radius, and a broader, asymmetric line best described by disk-like emission from $\sim 100\,\rm R_{g}$. This disk component mirrors the profile of the double-peaked H$\alpha$ line observed in the optical. In addition, we detect broadened Fe XXV and Fe XXVI emission lines whose inferred locations bridge the gap between the inner disk and the optical broad-line region. The weak narrow Fe K$\alpha$ equivalent width ($\rm EW = 32 \pm 6\,eV$) and absence of a Compton hump imply a low-covering-fraction, Compton-thin torus. Together, these results reveal a radially stratified structure in NGC 7213, spanning nearly four orders of magnitude in radius, and place the source in an intermediate accretion state ($\rm \lambda_{Edd} = 0.001-0.01$) where the inner disk and BLR remain, while the torus shows signs of dissipation.