To be or not to be a blazar. The case of the Narrow-Line Seyfert 1 SBS
  0846+513
  The presence of a relativistic jet in some radio-loud Narrow-Line Seyfert 1s
(NLSy1) galaxies, first suggested by their variable radio emission and the flat
radio spectra, is now confirmed by the Fermi-LAT detection of five NLSy1s in
gamma rays. In particular, a strong gamma-ray flare from SBS 0846+513 was
observed in 2011 June by Fermi-LAT reaching a gamma-ray luminosity (0.1-300
GeV) of about 10^48 erg/s, comparable to that of bright flat spectrum radio
quasars. Apparent superluminal velocity in the jet was inferred from 2011-2012
VLBA images, suggesting the presence of a highly relativistic jet. Both the
power released by this object during the flaring activity and the apparent
superluminal velocity are strong indicators of the presence of a relativistic
jet as powerful as those in blazars. In addition, variability and spectral
properties in radio and gamma-ray bands indicate a blazar-like behaviour,
suggesting that, except for some distinct optical characteristics, SBS 0846+513
could be considered as a young blazar at the low end of the blazar's black hole
mass distribution.
