General Physical Properties of Gamma-Ray-emitting Narrow-line Seyfert 1 Galaxies

We present the results of a detailed multi-wavelength study of a sample of sixteen narrow-line Seyfert 1 (NLSy1) galaxies known in $\gamma$-rays so far. This includes a focused X-ray spectral analysis, to compare them with a more general NLSy1 population, and a broadband spectral energy distribution (SED) modeling considering the leptonic radiative processes to understand their similarity/dissimilarity with blazars. The X-ray spectra of $\gamma$-NLSy1 galaxies exhibit similarities both with typical NLSy1 sources below $\lesssim$2 keV and blazars at higher energies. We also find weak evidences of excess absorption in the soft X-ray spectra of 3 sources and a tentative detection of Fe line in 1H~0323+342. A comparison of the broadband parameters derived from the SED modeling reveals the similarity of $\gamma$-NLSy1 objects with blazars, in particular more with flat spectrum radio quasars. The $\gamma$-NLS1 galaxies host relatively low power jets with small bulk Lorentz factors with respect to blazars and this explains the paucity of such sources in the $\gamma$-ray catalogs and identification of an even fewer parent population members. Many of the observed features of these intriguing objects suggest they host low-mass black holes. The accretion rate in Eddington units can be considered as the driving factor to explain the physical properties of $\gamma$-NLSy1 sources, similar to that which is known for general blazar population.