The physical properties of candidate neutrino-emitter blazars

¹ Julius-Maximilians-Universität Würzburg, Fakultät für Physik und Astronomie, Institut für Theoretische Physik und Astrophysik, Lehrstuhl für Astronomie, Emil-Fischer-Str. 31, D-97074 Würzburg, Germany
² Deutsches Elektronen-Synchrotron DESY, Platanenallee 6, 15738 Zeuthen, Germany
³ Université Paris Cité, CNRS, Astroparticule et Cosmologie, F-75013 Paris, France

^⋆ Corresponding author: alessandra.azzollini@uni-wuerzburg.de

Received: 1 July 2024
Accepted: 4 July 2025

Abstract

Context. The processes governing the production of astrophysical high-energy neutrinos are still a matter of debate, and the sources that originate them remain an open question. Among the putative emitters, active galactic nuclei (AGN) have gained increasing attention in recent years. Blazars, in particular, stand out due to their capability of accelerating particles in environments with external radiation fields. Recent observations suggest that they may play a role in the production of high-energy neutrinos detected by the IceCube observatory.

Aims. We studied the physical properties of a subsample of 52 blazars, that have been proposed as candidate neutrino emitters, based on a positional cross-correlation statistical analysis between IceCube hotspots and the Fifth Edition of the Roma BZCat catalog. We provide a first characterization of their central engines and inner physical nature, which may help to explore the potential link with neutrino production.

Methods. This study carries out an analysis of the optical spectroscopic properties of a sample of 52 candidate neutrino-emitter blazars, to infer their accretion regime. It is complemented by data at the radio and γ-ray frequencies, which carry the information about the intrinsic power of the relativistic jet. We compared the properties of the sample of candidate neutrino-emitter blazars to other blazar samples from the literature. To this end, we performed statistical tests and also explored, through simulations, the applicability of methods that include limits (censored data) on the quantities of our interest.

Results. Overall, the sample of candidate neutrino-emitter blazars displays properties compatible with those of the reference samples. We observe a mild tendency to prefer objects with intense radiation fields (which are typical of radiatively efficient accretors), and high radio power, such as high-excitation radio galaxies (HERGs). Among the blazars in our sample, 24 are detected in γ-rays; they cover various ranges of γ-ray luminosities, compatible with the overall population. Additionally, we show that the statistical tests commonly used in the literature need to be used with caution, as they are highly sensitive to the amount of censored data and the sample size.