The Spectra of IceCube Neutrino (SIN) candidate sources

V. Modeling and interpretation of multiwavelength and neutrino data

¹ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching bei München, Germany
² Excellence Cluster ORIGINS, Boltzmannstr. 2, 85748 Garching bei München, Germany
³ Technische Universität München, TUM School of Natural Sciences, Physics Department, James-Frank-Str. 1, 85748 Garching bei München, Germany
⁴ Institute for Advanced Study, Technische Universität München, Lichtenbergstrasse 2a, 85748 Garching bei München, Germany
⁵ Center for Astrophysics and Space Science (CASS), New York University Abu Dhabi, PO Box 129188 Abu Dhabi, UAE
⁶ Associated with INAF, Osservatorio Astronomico di Brera, Via Brera, 28, 20121 Milano, Italy
⁷ INAF – IASF Palermo, Via Ugo La Malfa, 153, 90146 Palermo, Italy
⁸ INAF – IASF Milano, Via Corti 12, 20133 Milano, Italy
⁹ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹⁰ Department of Physics, National and Kapodistrian University of Athens, University Campus Zografos, 15783 Athens, Greece
¹¹ Institutt for fysikk, Norwegian University of Science and Technology (NTNU), 7491 Trondheim, Norway

Received: 2 May 2024
Accepted: 3 June 2024

Abstract

Context. A correlation has been reported between the arrival directions of high-energy IceCube events and γ-ray blazars classified as intermediate- and high-synchrotron-peaked BL Lacs. Subsequent studies have investigated the optical properties of these sources, compiled and analyzed public multiwavelength data, and constrained their individual neutrino emission based on public IceCube point-source data.

Aims. We provide a theoretical interpretation of public multiwavelength and neutrino point source data for the 32 BL Lac objects in the sample previously associated with an IceCube alert event. We combined the individual source results to draw conclusions regarding the multimesssenger properties of the sample and the required power in relativistic protons.

Methods. We performed particle interaction modeling using open-source numerical simulation software. We constrained the model parameters using a novel and unique approach that simultaneously describes the host galaxy contribution, the observed synchrotron peak properties, the average multiwavelength fluxes, and, where possible, the IceCube point source constraints.

Results. We show that a single-zone leptohadronic model can describe the multiwavelength broadband fluxes from all 32 IceCube candidates. In some cases, the model suggests that hadronic emission may contribute a considerable fraction of the γ-ray flux. The required power in relativistic protons ranges from a few percent to a factor of ten of the Eddington luminosity, which is energetically less demanding compared to other leptohadronic blazar models in recent literature. The model can describe the 68% confidence level IceCube flux for a large fraction of the masquerading BL Lacs in the sample, including TXS 0506+056; whereas, for true BL Lacs, the model predicts a low neutrino flux in the IceCube sensitivity range. Physically, this distinction is due to the presence of photons from broad line emission in masquerading BL Lacs, which increase the efficiency of hadronic interactions. The predicted neutrino flux peaks between a few petaelectronvolt and 100 PeV and scales positively with the flux in the gigaelectronvolt, megaelectronvolt, X-ray, and optical bands. Based on these results, we provide a list of the brightest neutrino emitters, which can be used for future searches targeting the 10–100 PeV regime.