Possible contributions of two nearby blazars to the NGC 4151 neutrino hotspot

¹ Ruhr University Bochum, Faculty of Physics and Astronomy, Astronomical Institute (AIRUB), Universitätsstraße 150, 44801 Bochum, Germany
² Department of Earth and Space Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan
³ Interdisciplinary Theoretical & Mathematical Science Program (iTHEMS), RIKEN, 2-1 Hirosawa, Saitama 351-0198, Japan
⁴ Kavli Institute for the Physics and Mathematics of the Universe (WPI), UTIAS, The University of Tokyo, Kashiwa, Chiba 277-8583, Japan

^⋆ Corresponding authors; omeliukh@astro.rub.de

Received: 14 November 2024
Accepted: 6 January 2025

Abstract

Context. The origin of the high-energy astrophysical neutrinos discovered by IceCube remains unclear, with both blazars and Seyfert galaxies emerging as potential sources. Recently, the IceCube Collaboration reported a ∼3σ neutrino signal from the direction of the nearby Seyfert galaxy NGC 4151. However, two gamma-ray-loud BL Lac objects, 4FGL 1210.3+3928 and 4FGL J1211.6+3901, lie close to NGC 4151, at angular distances of 0.08° and 0.43°, respectively.

Aims. We investigated the potential contribution of these two blazars to the observed neutrino signal from the direction of NGC 4151 and assessed their detectability with future neutrino observatories.

Methods. We modeled the multiwavelength spectral energy distributions (SEDs) of both blazars using a self-consistent numerical radiation code, AM³. We calculated their neutrino spectra and compared them to the measured NGC 4151 neutrino spectrum and future neutrino detector sensitivities.

Results. The SED of 4FGL 1210.3+3928 revealed a feature that cannot be explained with a purely leptonic model, suggesting the presence of protons in the jet. Our model predicts neutrino emission peaking above ∼10¹⁷ eV with fluxes of ∼10⁻¹² erg cm⁻² s⁻¹ for this source. The SED of 4FGL J1211.6+3901 can be explained with both leptonic and leptohadronic models. The contribution of these two blazars to the ∼10 TeV neutrino signal observed from the direction of NGC 4151 can only be minor. Still, future radio-based neutrino telescopes such as IceCube-Gen2’s radio array and GRAND may be able to detect high-energy neutrinos from these two potential neutrino sources.