2024MNRAS.532.3729L

In this work, we explore the connection of three jetted $\gamma -$loud AGNs classes: Compact steep-spectrum sources (CSS), Narrow-line Seyfert 1 (NLS1), and flat-spectrum radio quasars, through the modelling of the spectral energy distribution (SED). We selected two sources identified as CSS/NLS1 hybrids, PKS 2004-440 and 3C 286. Additionally, we included the source PKS 0440-00, initially classified as an FSRQ in the first Fermi-LAT catalogue, but recently reclassified as an NLS1. We present the results of their broadband SED modelling using a one-zone leptonic synchrotron-self Compton (SSC) + external Compton (EC) model. By exploring the parameter space and investigating the disc-jet connection in these sources, we analyse their classification in a model-dependent way. Our findings reveal that modeling PKS 2004-447 at relatively large angles, as expected for CSS, results in an SSC-dominated inverse Compton emission. In contrast, at low-observing angles, the inverse Compton emission is dominated by external photon fields. Both scenarios result in a jet with a low-radiative power. For 3C 286, we found that using a one-zone model limits the jet viewing angle to $\sim 7^{\circ }$, mainly due to its impact on the $\gamma$-ray emission. Our model results show a magnetically dominated jet, consistent with $\gamma$-CSS sources. Our results suggest that PKS 0440-00, can be classified as a powerful $\gamma -$NLS1, characterized by high accretion power and a jet dominated by bulk motion, similar to FSRQs.