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A small fraction of Narrow Line Seyfert 1s (NLSy1s) are observed to begamma-ray emitters. Understanding the properties of these sources is ofinterest 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 mostrecently discovered gamma-ray emitting NLSy1s. We analyse an ~80 ks XMM-Newtonobservation obtained in 2017, as well as quasi-simultaneous multi-wavelengthobservations covering the radio - gamma-ray range. The spectral energydistribution of the source is similar to the other gamma-ray NLSy1s, confirmingits blazar-like nature. The X-ray spectrum is characterised by a hard photonindex (Gamma = 1.66) above 2 keV and a soft excess at lower energies.The hardphoton index provides clear evidence that inverse Compton emission from the jetdominates the spectrum, while the soft excess can be explained by acontribution from the underlying Seyfert emission. This contribution can befitted by reflection of emission from the base of the jet, as well as byComptonisation in a warm, optically thick corona. We discuss our results in thecontext of the other gamma-ray NLSy1s and note that the majority of them havesimilar X-ray spectra, with properties intermediate between blazars andradio-quiet NLSy1s.

FBQS J1644+2619: multiwavelength properties and its place in the class of gamma-ray emitting Narrow Line Seyfert 1s