The Broad-band X-ray Spectrum of IC 4329A from a Joint NuSTAR/Suzaku Observation

TL;DR

This study presents a detailed spectral analysis of IC 4329A using simultaneous NuSTAR and Suzaku observations, constraining the X-ray continuum, absorption, reflection, and coronal properties, revealing variability in Fe Kα line strength and coronal temperature.

Contribution

First simultaneous NuSTAR and Suzaku spectral analysis of IC 4329A, providing robust constraints on the X-ray continuum, absorption, reflection, and coronal parameters.

Findings

Modest absorption column of 6 x 10^21 cm^-2 with no significant Fe K band curvature.

Detected a narrow Fe Kα line with specific energy, width, and equivalent width, but limited constraints on relativistic reflection.

Updated high-energy cutoff measurement at 186 keV, leading to estimates of coronal temperature and optical depth for different geometries.

Abstract

We have obtained a deep, simultaneous observation of the bright, nearby Seyfert galaxy IC 4329A with Suzaku and NuSTAR. Through a detailed spectral analysis, we are able to robustly separate the continuum, absorption and distant reflection components in the spectrum. The absorbing column is found to be modest at $N_H = 6 \times 10^{21}$ cm$^2$, and does not introduce any significant curvature in the Fe K band. We are able to place a strong constraint on the presence of a broadened Fe K{\alpha} line: $E = 6.46^{+0.08}_{-0.07}$ keV rest frame with ${\sigma} = 0.33^{+0.08}_{-0.07}$ keV and $EW = 34^{+8}_{-7}$ eV, though we are not able to constrain any of the parameters of a relativistic reflection model. These results highlight the range in broad Fe K{\alpha} line strengths observed in nearby, bright AGN (roughly an order of magnitude), and imply a corresponding range in the physical properties of the inner accretion disk in these sources. We have also updated our previously reported measurement of the high-energy cutoff of the hard X-ray emission using both observatories rather than just NuSTAR alone: $E_{cut} = 186 \pm 14$ keV. This high-energy cutoff acts as a proxy for the temperature of the coronal electron plasma, enabling us to further separate this parameter from the optical depth of the plasma and to update our results for these parameters as well. We derive $kT = 50^{+6}_{-3}$ keV with ${\tau} = 2.34^{+0.16}_{-0.11}$ using a spherical geometry, $kT = 61 \pm 1$ keV with ${\tau} = 0.68 \pm 0.02$ for a slab geometry, with both having an equivalent goodness-of-fit.