A few decades have passed since the identification of narrow-line Seyfert 1 (NLS1) galaxies as a subclass of active galactic nuclei (AGN). NLS1s show a Seyfert 1-like spectrum, but with emission line widths similar to those of Seyfert 2 spectra. These peculiar traits suggest a combination of factors: high accretion rates near the Eddington limit and low-mass black holes. Although few, jetted NLS1s have been discovered. Recently, seven sources with an inverted radio spectrum and extreme radio variability were identified, among a sample of radio-quiet and radio-silent jetted NLS1s. They show rapid high-frequency flares at 37 GHz that increase their flux density up to 9000-fold (Jy level) with an e-folding timescale of less than 10 hours. During quiescence and at lower frequencies, they achieve only mJy levels. Until now, their radio spectra are the only common feature. I will present the results of a multi-epoch analysis, devoted to search optical variability and periodicities using publicly available data. For this purpose I performed Fourier analyses, to find any similarity between such extreme flaring objects. Moreover, a long-term variability comparison between radio and optical light curves, and an optical spectra analysis have been carried out. Beside these the role of the Sardinia Radio Telescope in the timescale hunting will be presented. Such strong radio variability had never been observed before in any AGN, making this work an important key to understanding the phenomenon. Furthermore, understanding the physics behind these peculiar objects may ultimately help us reveal a new and unexplored population of jetted AGN.

Breve CV di Luca Crepaldi:

PhD student in Astronomia presso l'Università degli Studi di Padova. Laurea Triennale in 'Astronomia' e Laurea Magistrale in 'Astrophysics and Cosmology' conseguite presso l'Università degli Studi di Padova, con una parziale collaborazione con il Metsähovi Radio Observatory (Finlandia). Topic: Narrow-line Seyfert 1 galaxies in studi multiwavelength, principalmente nella banda ottica e radio. All'attivo circa 50 notti di osservazioni con telescopi ottici (UT4 in Paranal observatory, NTT in La Silla observatory, Tel. Galileo e Copernico in Asiago observatory).