Larsson, J.J.LarssonD'AMMANDO, FILIPPOFILIPPOD'AMMANDOFalocco, S.S.FaloccoGIROLETTI, MARCELLOMARCELLOGIROLETTIORIENTI, MonicaMonicaORIENTIPICONCELLI, EnricoEnricoPICONCELLIRIGHINI, SIMONASIMONARIGHINI2020-10-052020-10-0520180035-8711http://hdl.handle.net/20.500.12386/27562A small fraction of Narrow Line Seyfert 1s (NLSy1s) are observed to be γ-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 multifrequency analysis of FBQS J1644+2619, one of the most recently discovered γ-ray emitting NLSy1s. We analyse an ∼80 ks XMM-Newton observation obtained in 2017, as well as quasi-simultaneous multiwavelength observations covering the radio-γ-ray range. The spectral energy distribution of the source is similar to the other γ-ray NLSy1s, confirming its blazar-like nature. The X-ray spectrum is characterized by a hard photon index (Γ = 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 Comptonization in a warm, optically thick corona. We discuss our results in the context of the other γ-ray NLSy1s and note that the majority of them have similar X-ray spectra, with properties intermediate between blazars and radio-quiet NLSy1s.STAMPAenArticle10.1093/mnras/sty2412-s2.0-85043514539000429276700004https://academic.oup.com/mnras/article-abstract/476/1/43/48324902018MNRAS.476...43LFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation::PE9_6 Stars and stellar systems