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-Newton , 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 \sim 7 ^ { \prime \prime } 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 in PKS 0558–504 .
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 } = 2.5 \times 10 ^ { 8 } ~ { } { M _ { \odot } } , 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 .