Investigating powerful jets in radio-loud Narrow Line Seyfert 1s

We report results on multiband observations from radio to gamma-rays of the two radio-loud narrow-line Seyfert 1 (NLSy1) galaxies PKS 2004-447 and J1548+3511. Both sources show a core-jet structure on parsec scale, while they are unresolved at the arcsecond scale. The high core dominance and the high variability brightness temperature make these NLSy1 galaxies good gamma-ray source candidates. Fermi-LAT detected gamma-ray emission only from PKS 2004-447, with a gamma-ray luminosity comparable to that observed in blazars. No gamma-ray emission is observed for J1548+3511. Both sources are variable in X-rays. J1548+3511 shows a hardening of the spectrum during high activity states, while PKS 2004-447 has no spectral variability. A spectral steepening likely related to the soft excess is hinted below 2 keV for J1548+3511, while the X-ray spectra of PKS 2004-447 collected by XMM-Newton in 2012 are described by a single power-law without significant soft excess. No additional absorption above the Galactic column density or the presence of an Fe line is detected in the X-ray spectra of both sources.Comment: 16 pages, 8 figures, accepted for publication in MNRA