FBQS J1644+2619: multiwavelength properties and its place in the class
  of gamma-ray emitting Narrow Line Seyfert 1s
  A small fraction of Narrow Line Seyfert 1s (NLSy1s) are observed to be
gamma-ray emitters. Understanding the properties of these sources is of
interest since the majority of NLSy1s are very different from typical blazars.
Here, we present a multi-frequency analysis of FBQS J1644+2619, one of the most
recently discovered gamma-ray emitting NLSy1s. We analyse an ~80 ks XMM-Newton
observation obtained in 2017, as well as quasi-simultaneous multi-wavelength
observations covering the radio - gamma-ray range. The spectral energy
distribution of the source is similar to the other gamma-ray NLSy1s, confirming
its blazar-like nature. The X-ray spectrum is characterised by a hard photon
index (Gamma = 1.66) above 2 keV and a soft excess at lower energies.The hard
photon index provides clear evidence that inverse Compton emission from the jet
dominates the spectrum, while the soft excess can be explained by a
contribution from the underlying Seyfert emission. This contribution can be
fitted by reflection of emission from the base of the jet, as well as by
Comptonisation in a warm, optically thick corona. We discuss our results in the
context of the other gamma-ray NLSy1s and note that the majority of them have
similar X-ray spectra, with properties intermediate between blazars and
radio-quiet NLSy1s.
