Where are Compton-thick radio galaxies? A hard X-ray view of three candidates

TL;DR

This study analyzes the X-ray spectra of three radio-loud active galactic nuclei candidates to determine their absorption levels, finding none are truly Compton-thick, and reviews the rarity of heavily absorbed radio-loud AGNs.

Contribution

The paper provides detailed broad-band X-ray spectral analysis of three candidates, challenging previous classifications and highlighting the scarcity of confirmed heavily absorbed radio-loud AGNs.

Findings

All three sources have absorption below the Compton-thick threshold.

No strong reflection continuum or iron K alpha line detected.

Current evidence for heavily absorbed radio-loud AGNs is limited.

Abstract

We present a broad-band X-ray spectral analysis of the radio-loud active galactic nuclei NGC 612, 4C 73.08 and 3C 452, exploiting archival data from NuSTAR, XMM-Newton, Swift and INTEGRAL. These Compton-thick candidates are the most absorbed sources among the hard X-ray selected radio galaxies studied in Panessa et al. (2016). We find an X-ray absorbing column density in every case below $1.5 \times 10^{24}$ cm$^{-2}$, and no evidence for a strong reflection continuum or iron K $\alpha$ line. Therefore, none of these sources is properly Compton-thick. We review other Compton-thick radio galaxies reported in the literature, arguing that we currently lack strong evidences for heavily absorbed radio-loud AGNs.