The NuSTAR View of Nearby Compton-thick AGN: The Cases of NGC 424, NGC 1320 and IC 2560

TL;DR

This study uses NuSTAR X-ray observations to analyze three nearby Compton-thick AGN, revealing their obscured nature, reflection-dominated spectra, and properties of their surrounding torus, enhancing understanding of heavily obscured active galaxies.

Contribution

First detailed spectral modeling of these three Compton-thick AGN with NuSTAR, constraining their reflection components and intrinsic properties for the first time.

Findings

All three AGN are obscured by Compton-thick material with N_H > 5 x 10^{24} cm^{-2}

Their spectra are dominated by reflection from the obscuring torus

Intrinsic luminosities are consistent with broadband spectral energy distributions

Abstract

We present X-ray spectral analyses for three Seyfert 2 active galactic nuclei, NGC 424, NGC 1320, and IC 2560, observed by NuSTAR in the 3-79 keV band. The high quality hard X-ray spectra allow detailed modeling of the Compton reflection component for the first time in these sources. Using quasi-simultaneous NuSTAR and Swift/XRT data, as well as archival XMM-Newton data, we find that all three nuclei are obscured by Compton-thick material with column densities in excess of ~5 x $10^{24}$ cm$^{-2}$, and that their X-ray spectra above 3 keV are dominated by reflection of the intrinsic continuum on Compton-thick material. Due to the very high obscuration, absorbed intrinsic continuum components are not formally required by the data in any of the sources. We constrain the intrinsic photon indices and the column density of the reflecting medium through the shape of the reflection spectra. Using archival multi-wavelength data we recover the intrinsic X-ray luminosities consistent with the broadband spectral energy distributions. Our results are consistent with the reflecting medium being an edge-on clumpy torus with a relatively large global covering factor and overall reflection efficiency of the order of 1%. Given the unambiguous confirmation of the Compton-thick nature of the sources, we investigate whether similar sources are likely to be missed by commonly used selection criteria for Compton-thick AGN, and explore the possibility of finding their high-redshift counterparts.