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Fermi-LAT observations provide continuous and regularly-sampled measurementsof gamma-ray photon flux for hundreds of blazars. Many of these light curves,spanning almost 15 years, have been thoroughly examined for periodicity inmultiple studies. However, the possibility that blazars may exhibit irregularlyrepeating flaring patterns in their gamma-ray light curves has not beensystematically explored. In this study, we aim to find repeating episodes offlaring activity in the 100 brightest blazars using Fermi-LAT light curves withvarious integration times. We use a Bayesian Blocks representation to convertthe time series into strings of symbols and search for repeating sub-stringsusing a fuzzy search algorithm. As a result, we identify 27 repeated episodesin the gamma-ray light curves of 10 blazars. We find that the patterns are mostlikely produced in structured jets composed of a fast spine and a slowersheath. When individual emission features propagate in the spine, they scatterseed photons produced in the non-uniform sheath through the inverse Comptonmechanism, resulting in a set of gamma-ray flares with a similar profile everysuch passage. Additionally, we explore the theoretically-predicted possibilitythat the spine-sheath structure facilitates the production of high-energyneutrinos in blazar jets. Using the catalogue of track-like events detected bythe IceCube neutrino telescope, we find evidence supporting this hypothesis ata $2.8\sigma$ significance level.

Repeated patterns of gamma-ray flares suggest structured jets of blazars as likely neutrino sources