Relativistic iron K alpha line detection in the Suzaku spectra of IC 4329A

TL;DR

This study analyzes Suzaku spectra of IC 4329A, revealing both narrow and broad iron K alpha lines, with the broad component likely originating from the inner accretion disk affected by relativistic effects.

Contribution

First detection of a relativistic broad iron K alpha line in IC 4329A using high-quality Suzaku data, demonstrating the line's subtlety and the importance of stacked residuals.

Findings

Narrow Fe K alpha line at 6.4 keV with EW=57 eV

Broad iron K alpha line with EW=124 eV, likely from the inner accretion disk

Presence of a narrow FeXXVI emission line at 6.94 keV

Abstract

We present an analysis of five Suzaku observations of the bright Seyfert1 galaxy IC 4329A. The broad energy band and high signal-to-noise ratio of the data give new constraints on the iron K alpha line profile and its relationship with the Compton hump at higher energies. The Fe K bandpass is dominated by a narrow core (EW=57 eV) at 6.4 keV consistent with neutral material. Using a physically-motivated model, our analysis also reveals the presence of a broad Iron K alpha line (EW=124 eV), most likely produced in the inner part of the accretion disk and blurred by general relativistic effects. This component is not immediately evident from the individual spectra, but is clearly present in the stacked residuals of all five observations, and has high statistical significance. This highlights the difficulty in identifying broad iron lines in AGN, even in data with very high signal-to-noise ratio, as they are difficult to disentangle from the continuum. The data are consistent with the narrow and broad iron line components tracking the Compton Hump, but do not provide clear evidence that this is the case. An additional narrow FeXXVI emission line at 6.94 keV is also seen, suggesting the presence of ionized material relatively distant from the central region. There is also a hint of variability, so the precise origin of this line remains unclear.