Flat Spectrum Radio Quasars as high-energy neutrino sources

TL;DR

This study finds a significant correlation between flat-spectrum radio quasars and high-energy neutrino events, suggesting FSRQs as potential sources of astrophysical neutrinos through jet-related mechanisms.

Contribution

It provides the first evidence of a moderate correlation between FSRQs and neutrino events, highlighting jets as likely emission sites, unlike radio-quiet quasars.

Findings

Moderate 2.7 sigma correlation between FSRQs and neutrinos.

Significant 4 sigma deviation in high-declination neutrino distribution.

Over 60% of IceCube neutrinos may originate from FSRQs.

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 (2.7 sigma) 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 deg. In particular, using the Kolmogorov-Smirnov test, we find that the high-declination event distribution deviates strongly (4 sigma) 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.