B2 0954+25A: a typical Fermi blazar or a gamma-loud Narrow Line Seyfert 1

Abstract

B2 0954+25A, detected by the {\it Fermi} satellite, is a blazar with interesting observational properties: it has been observed to transit from a jet dominated to a disk dominated state; its radio spectrum appears flat at all observing frequencies (down to 74 MHz); optically, the H$\beta$ line profile is asymmetric. The flatness of radio spectrum suggests that the isotropic emission from radio lobes is very weak, despite the large size of its jet ($\gtrsim$ 500 kpc). Its broad--band spectral energy distribution is surprisingly similar to that of the prototypical $\gamma$--ray, radio loud, Narrow Line Seyfert 1 ($\gamma$--NLS1) galaxy PMN J0948+0022. In this work we revisit the mass estimates of B2 0954+25A considering only the symmetric component of the H$\beta$ line and find (1--3) $\times 10^8$ M$_{\sun}$. In light of our composite analysis, we propose to classify the source as a transition object between the class of Flat Spectrum Radio Quasar and $\gamma$--ray, radio loud NLS1. A comparison with two members of each class (3C 273 and PMN J0948+0022) is discussed.