Very High Energy gamma rays from AGNs: key for AGN structure and cosmological studies

Only around 60 AGNs have been detected so far at Very High Energy (VHE, E>100 GeV) gamma rays, most of them being blazars (AGNs which relativistic jet point in the direction to the Earth). Among them only five Flat Spectrum Radio Quasars (FSRQs) have been observed in the VHE band, all of them detected by the MAGIC telescopes located at Roque de los Muchachos Observatory (La Palma). Despite the difficulty of their detection, FSRQs offer a unique physics scenario to test the AGN structure thanks to their intrinsic gamma-ray absorption within their Broad Line Region (BLR). Gamma-ray blazars are one of the most powerful accelerators of the Universe, and besides the study of their intrinsic properties, blazars can be used as cosmic lighthouses to probe the cosmic backgrounds as the extragalactic background light (EBL) and the intergalactic magnetic field (IGMF). An overview of the of the study of VHE FSRQs in a multi-wavelength context as well as the role of VHE blazars on cosmological studies will be discussed.