Flat-spectrum radio quasars as high-energy neutrino sources

INAF – Osservatorio Astronomico di Brera, via Brera 28, Milano, Italy

^★ Corresponding authors: alberto.moretti@inaf.it; alessandro.caccianiga@inaf.it

Received: 14 March 2025
Accepted: 13 October 2025

Abstract

The astrophysical sources responsible for the production of high-energy neutrinos remain largely uncertain. The strongest associations suggest a correlation between neutrinos and active galactic nuclei. However, it is still unclear which specific regions and mechanisms of the accreting supermassive black hole are responsible for their production. In this paper we investigate the correlation between the positions of IceCat-1 neutrino events and a large, optically selected quasar catalogue extracted from the Sloan Digital Sky Survey. Within this sample, we distinguish radio-quiet quasars from flat-spectrum radio quasars (FSRQs) based on radio emission data from the Cosmic Lens All Sky Survey (CLASS) catalogue. While all the associations between neutrino events and radio-quiet quasars are consistent with being random matches, FSRQs exhibit a moderately significant correlation (∼2.7σ) with neutrino positions. Additionally, we observe that the distribution of minimum distances between neutrino events and FSRQs differs significantly for events at declinations above and below 20°. In particular, using the Kolmogorov-Smirnov test, we find that the high-declination event distribution deviates strongly (4σ) from a random distribution. We interpret all these results as an indication that a large fraction of the neutrino events (> 60%) observed by IceCube could be produced by the FSRQs and that the emission mechanism is likely related to the relativistic jets rather than the radio-quiet component of these sources, such as the accretion disk or corona.