Gamma-ray emitting narrow-line Seyfert 1 galaxies: Past, present, and future

Abstract

This article reviews our current understanding about γ-ray detected narrow-line Seyfert 1 (γ-NLSy1) galaxies. The detection with the Large Area Telescope onboard Fermi Gamma-ray Space Telescope has provided the strongest evidence for the presence of closely aligned relativistic jet in these intriguing active galactic nuclei (AGN) and opened up a realm to explore the physical conditions needed to launch the jet in a different central engine and host galaxy environment than that is known for blazars. Promising results acquired from various multi-wavelength campaigns are converging to a scenario in which the γ-NLSy1 galaxies can be considered as 'young' blazars. These enigmatic sources hold the key to unravel the jet triggering mechanism and evolution of the AGN phase of a galaxy, in general. As such, γ-NLSy1s should be considered as one of the top priority targets for next generation observational facilities.