Relationship between Gamma-ray loudness and X-ray spectra of Radio Galaxies

TL;DR

This study compares X-ray spectral properties of GeV-loud and GeV-quiet radio galaxies, revealing differences in absorption and implications for jet orientation and emission visibility.

Contribution

It provides the first systematic analysis of X-ray spectra differences between GeV-loud and GeV-quiet radio galaxies using multi-satellite data.

Findings

Most GeV-loud RGs lack significant absorption.

Approximately 50% of GeV-quiet RGs show significant absorption.

Heavy absorption correlates with X-ray luminosity range of 10^{43}-10^{45} erg/s.

Abstract

The {\it Fermi} satellite has detected $\sim$60 radio galaxies (RGs). In this study, we investigate the difference in the properties of X-ray spectra between GeV-loud RGs and GeV-quiet RGs. Our sample comprises 68 objects: 36 RGs detected with {\it Fermi} and 32 RGs not detected with gamma rays. We analyzed the X-ray spectra of these 68 objects using data from the {\it XMM-Newton}, {\it Chandra}, {\it NuSTAR}, and {\it Swift} satellites. Our results show that most GeV-loud RGs do not exhibit significant absorption, while $\sim$50\% of the GeV-quiet RGs exhibit significant absorption. This suggests that the jet of GeV-loud RGs is viewed from a small angle, and thus the emission is not easily blocked by the torus. Moreover, we reported that RGs with a heavy absorption are mostly in the X-ray luminosity range of $10^{43}-10^{45}$erg s$^{-1}$; however, few RGs with lower and higher luminosity suffer from heavy absorption. This is the same trend as that of Seyfert galaxies.