# A discovery of young radio sources in the cores of giant radio galaxies selected at hard X-rays

## TL;DR

This study reveals a high prevalence of young, possibly restarting radio sources at the cores of giant radio galaxies selected via hard X-ray observations, suggesting a link between accretion activity and jet reactivation.

## Contribution

It is the first to identify a significant fraction of young radio sources in the cores of giant radio galaxies selected from hard X-ray catalogs.

## Key findings

- 61% of the studied nuclei are young radio sources.
- A potential connection between hard X-ray emission and jet reactivation.
- Evidence of restarting activity episodes in giant radio galaxy cores.

## Abstract

Giant Radio Galaxies (GRG) are the largest single entities in the Universe, having a projected linear size exceeding 0.7 Mpc, which implies that they are also quite old objects. They are not common, representing a fraction of only about 6% in samples of bright radio galaxies. While a census of about 300 of these objects has been built in the past years, still no light has been shed on the conditions necessary to allow such an exceptional growth, whether of environmental nature or linked to the inner accretion properties. Recent studies found that samples of radio galaxies selected from hard X-ray AGN catalogs selected from INTEGRAL/IBIS and Swift/BAT (thus at energies >20 keV) present a fraction of GRG four times larger than what found in radio-selected samples. We present radio observations of 15 nuclei of hard X-ray selected GRG, finding for the first time a large fraction (61%) of young radio sources at the center of Mpc-scale structures. Being at the center of GRG, these young nuclei may be undergoing a restarting activity episode, suggesting a link between the detected hard X-ray emission - due to the ongoing accretion - and the reactivation of the jets.