The relativistic jet of the gamma-ray emitting narrow-line Seyfert 1
  galaxy 1H 0323+342
  The detection of several radio-loud narrow-line Seyfert 1 (NLS1) galaxies by
the Fermi Gamma-Ray Space Telescope hints at the existence of a rare, new class
of gamma-ray emitting active galactic nuclei with low black hole masses. Like
flat spectrum radio quasars (FSRQs), their gamma-ray emission is thought to be
produced via the external Compton mechanism whereby relativistic jet electrons
upscatter a photon field external to the jet, e.g. from the accretion disc,
broad line region (BLR) and dusty torus, to higher energies. Here we study the
origin of the gamma-ray emission in the lowest-redshift candidate among the
currently-known gamma-ray emitting NLS1s, 1H 0323+342, and take a new approach.
We observationally constrain the external photon field using quasi-simultaneous
near-IR, optical and X-ray spectroscopy. Applying a one-zone leptonic jet
model, we simulate the range of jet parameters for which this photon field,
when Compton scattered to higher energies, can explain the gamma-ray emission.
We find that the site of the gamma-ray emission lies well within the BLR and
that the seed photons mainly originate from the accretion disc. The jet power
that we determine, $1.0 \times 10^{45}$ erg s$^{-1}$, is approximately half the
accretion disc luminosity. We show that this object is not simply a low-mass
FSRQ, its jet is intrinsically less powerful than predicted by scaling a
typical FSRQ jet by black hole mass and accretion rate. That gamma-ray emitting
NLS1s appear to host underpowered jets may go some way to explaining why so few
have been detected to date.
