Winds of Change: XRISM Resolve X-ray spectroscopy of NGC 4051

TL;DR

This paper presents high-resolution XRISM Resolve X-ray spectra of NGC 4051, revealing variable, high-velocity outflows likely driven by magnetic forces, providing insights into accretion disk winds in a low-mass Seyfert galaxy.

Contribution

First high-resolution XRISM spectrum of NGC 4051 showing detailed wind components and their variability, suggesting magnetic driving of outflows in a low-mass Seyfert galaxy.

Findings

Detected two blue-shifted Fe K absorption components with velocities of 0.025c and 0.04c.

Observed variability in wind velocity on sub-day timescales.

Wind likely driven by magnetic forces rather than radiation pressure.

Abstract

NGC 4051 is a nearby (16.7 Mpc), Narrow Line Seyfert 1 galaxy (NLS1), which has a low black hole mass of $10^6$ M$_{\odot}$. It is also known for its rapid X-ray variability, on timescales of kilo-seconds and has a complex, multi component wind in both the soft X-ray and Fe K bands. Here we present the first high resolution XRISM Resolve spectrum of NGC 4051, which was captured in a historically bright state for a 150 ks exposure. XRISM resolves two blue-shifted Fe K shell absorption troughs in the mean spectrum, which can be ascribed to H-like iron and arises from two outflow components with outflow velocities of 0.025c and 0.04c. A time dependent spectral analysis shows that the iron K absorption is variable on timescales of less than a day, increasing in velocity over the duration of the observation. The velocity changes may be explained either by the passage of two separate transiting absorbers, of different velocities, or by a single accelerating outflow of approximately constant column density. In the latter case, the wind acceleration is likely to be too large to be caused by radiation pressure and instead magnetic driving is favored to accelerate the wind up to 0.04c. The outflow can originate from an accretion disk wind, whose kinetic power is sub-Eddington in contrast to recent examples of winds from powerful, luminous quasars observed by XRISM.