XRISM finds the Changing-Look AGN NGC 1365 in an extended low state: A dense, highly ionized outflow obscures the central source

TL;DR

XRISM observations of NGC 1365 during a low-flux state reveal dense, highly ionized outflows and emission features, providing insights into the wind structure and its relation to the broad-line region.

Contribution

First XRISM/Resolve observations of NGC 1365 in a low state, detecting emission lines from a highly ionized wind and linking the X-ray and optical broad-line regions.

Findings

Detection of Fe XXV and Fe XXVI absorption and emission lines.

Estimated wind launch radius of about 10^16 cm.

Broadened Fe Kα line consistent with wind and broad-line region scales.

Abstract

We present the first XRISM/Resolve observations of the active galactic nucleus, NGC 1365, obtained in 2024 February and July. NGC 1365 is known for rapid transitions between Compton-thick and Compton-thin states, along with strong absorption from a highly ionized wind. During our observations, the source is found in a persistent low-flux state, characterized by a decrease in hard-X-ray luminosity and significant line-of-sight obscuration. In this state, XRISM/Resolve reveals clear Fe\,\textsc{xxv} and Fe\,\textsc{xxvi} absorption lines together with, for the first time in this source, corresponding emission lines. These features may arise either from reemission from a photoionized wind (P Cygni profile) or from collisionally ionized gas associated with outflow-driven shocks in the interstellar medium. We estimate the wind launch radius to be approximately $10^{16}~\mathrm{cm}$ ($\sim 10^4 R_{\mathrm{g}}$), consistent with the location of the X-ray broad-line region. We also resolve a broadened Fe K$\alpha$ line by $\sigma \sim 1300$ km s$^{-1}$ placing it at similar scales to the wind, consistent with radii inferred from disk-broadening models and the variability of the Fe K$\alpha$ broad line. The similarity of the Fe K$\alpha$ profile to the H$\beta$ wing and broad Pa$\alpha$ width indicates that the X-ray-emitting region is likely cospatial with the optical/IR broad-line region and originates from the same gas.