Accretion disc/corona emission from a radio-loud narrow-line Seyfert 1 galaxy PKS 0558–504

Abstract

Approximately 10-20% of Active Galactic Nuclei are known to eject powerful jets from the innermost regions. There is very little observational evidence if the jets are powered by spinning black holes and if the accretion disks extend to the innermost regions in radio-loud AGN. Here we study the soft X-ray excess, the hard X-ray spectrum and the optical/UV emission from the radio-loud narrow-line Seyfert 1 galaxy PKS 0558-504 using Suzaku and Swift observations. The broadband X-ray continuum of PKS 0558- 504 consists of a soft X-ray excess emission below 2 keV that is well described by a blackbody (kTe ~ 0.13 keV) and high energy emission that is well described by a thermal Comptonisation (compps) model with kTe ~ 250 keV, optical depth {\tau} ~ 0.05 (spherical corona) or kTe ~ 90 keV, {\tau} ~ 0.5 (slab corona). The Comptonising corona in PKS 0558-504 is likely hotter than in radio-quiet Seyferts such as IC 4329A and Swift J2127.4+5654. The observed soft X-ray excess can be modelled as blurred reflection from an ionised accretion disk or optically thick thermal Comptonisation in a low temperature plasma. Both the soft X-ray excess emission when interpreted as the blurred reflection and the optical/UV to soft X-ray emission interpreted as intrinsic disk Comptonised emission implies spinning (a > 0.6) black hole. These results suggest that disk truncation at large radii and retrograde black hole spin both are unlikely to be the necessary conditions for launching the jets.