A panchromatic view of PKS 0558-504: an ideal laboratory to study the disk-jet link

TL;DR

This study presents a comprehensive multi-wavelength analysis of PKS 0558-504, revealing its super-Eddington accretion, extended radio structure, and its analogy to Galactic black holes in a high accretion state, challenging jet-dominated emission models.

Contribution

It provides the first detailed broadband spectral energy distribution and accretion analysis of PKS 0558-504, linking its properties to Galactic black hole states and gamma-ray loud NLS1s.

Findings

PKS 0558-504 has extended radio lobes with low radio-loudness.

The source is accreting at super-Eddington rates.

Accretion power dominates over jet kinetic power.

Abstract

PKS 0558-504 is the brightest radio-loud Narrow-Line Seyfert 1 galaxy at X-ray energies. Here we present results from the radio, optical, UV, and X-ray bands obtained with Swift, XMM, and ATCA during a 10-day monitoring campaign in September 2008. The simultaneous coverage at several wavelengths makes it possible to investigate in detail the broadband spectral energy distribution (SED) and the energetic of this source. The main results can be summarized as follows. The ATCA reveals the presence of an extended radio emission in PKS 0558-504 with two lobe-like structures at ~7" from the bright central source. The extended radio structure and the low value of the radio-loudness similar to radio-quiet Seyfert galaxies coupled with constraints from higher energy bands argue against a jet-dominated emission. The study of the SED, which is dominated by a nearly constant optical-UV emission, supports the conclusion that PKS 0558-504 is accreting at super-Eddington rate. This conclusion was reached assuming M_BH=2.5e8 M_sun, which was obtained with a new scaling method based on X-ray spectral variability results. A comparison between the accretion luminosity and the kinetic power associated with the jet suggests that in this source the accretion power dominates in agreement with the results obtained from Radiation-MHD simulations of Galactic black holes (GBHs) accreting at the Eddington rate. The combined findings from this panchromatic investigation strongly suggest that PKS 0558-504 is a large-scale analog of GBHs in their highly accreting intermediate state. Importantly, PKS 0558-504 may also be the prototype of the parent population of the very radio-loud NLS1s recently detected at gamma-ray energies.