Relativistic reflection in NGC 4151

TL;DR

This study analyzes the X-ray spectrum of NGC 4151, revealing relativistic reflection from a truncated accretion disk at certain states, and challenges previous models suggesting emission near the black hole horizon.

Contribution

It provides new insights into the geometry of the accretion disk and the origin of X-ray reflection in NGC 4151, especially regarding disk truncation and relativistic effects.

Findings

Relativistic reflection detected in bright states

Narrow Fe Kalpha line from Compton-thin matter

No evidence for reflection near the black hole horizon

Abstract

We investigate the X-ray spectrum of the Seyfert galaxy NGC 4151 using the simultaneous Suzaku/NuSTAR observation and flux-resolved INTEGRAL spectra supplemented by Suzaku and XMM observations. Our best spectral solution indicates that the narrow Fe Kalpha line is produced in Compton-thin matter at the distance of several hundred gravitational radii. In such a model, we find a weak but significant relativistic reflection from a disk truncated at about ten gravitational radii when the source is in bright X-ray states. We do not find evidence either for or against the presence of relativistic reflection in the dim X-ray state. We also rule out models with X-ray emission dominated by a source located very close to the black hole horizon, which was proposed in previous works implementing the lamp-post geometry for this source. We point out that accurate computation of the thermal Comptonization spectrum and its distortion by strong gravity is crucial in applications of the lamp-post geometry to the NuSTAR data.