Multimessenger flare in the quasar PKS 0446+11

¹ Max Planck Institute for Radio Astronomy, Auf dem Hügel 69, D–53121 Bonn, Germany
² Department of Astronomy, University of Michigan, 323 West Hall, 1085 S. University Avenue, Ann Arbor, MI 48109, USA
³ Special Astrophysical Observatory of the Russian Academy of Sciences, Nizhny Arkhyz, 369167, Russia
⁴ Instituto de Astrofísica de Andalucía-CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
⁵ Department of Physics and Astronomy, Denison University, Granville, OH 43023, USA
⁶ Institute for Nuclear Research, 60th October Anniversary Prospect 7a, Moscow 117312, Russia
⁷ Lebedev Physical Institute, Leninskiy prospekt 53, Moscow 119991, Russia
⁸ Department of Physics and Astronomy, Purdue University, 525 Northwestern Avenue, West Lafayette, IN 47907, USA
⁹ CePIA, Astronomy Department, Universidad de Concepción, Casilla 160-C, Concepción, Chile
¹⁰ Black Hole Initiative, Harvard University, 20 Garden St, Cambridge, MA 02138, USA
¹¹ Moscow Institute of Physics and Technology, Dolgoprudny, Institutsky per., 9 Moscow region, 141700, Russia
¹² Crimean Astrophysical Observatory, 298409 Nauchny, Crimea
¹³ Owens Valley Radio Observatory, California Institute of Technology, Pasadena, CA 91125, USA
¹⁴ Physics Department, Lomonosov Moscow State University, 1-2 Leninskie Gory, Moscow 119991, Russia

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 6 November 2025
Accepted: 27 March 2026

Abstract

Context. The physical mechanisms driving neutrino and electromagnetic flares in blazars remain poorly understood.

Aims. We investigate a prominent multimessenger flare in the quasar PKS 0446+11 to identify the processes responsible for its high-energy emission.

Methods. We analyzed the IceCube-240105A high-energy neutrino event together with contemporaneous observations in the gamma-ray, X-ray, optical, and radio bands. We modeled the on- and off-flare spectral energy distributions (SEDs) within a single-zone leptohadronic framework. Multi-epoch VLBA observations from the MOJAVE program provide parsec-scale polarization data that complement the multiwavelength light curves.

Results. No significant time delay was detected between the neutrino arrival and the flares in different energy bands. This is consistent with an extremely small jet viewing angle below 1 deg, inferred from the parsec-scale polarization structure. The flare can be reproduced by the injection of a proton population and an increase in the Doppler factor from 18 to 24. We also detected an approximately 90 deg rotation of the EVPA in the parsec-scale core during the initial phase of the flare, indicating the emergence of a shock formed by the change in the bulk plasma speed.

Conclusions. Our comprehensive multimessenger analysis demonstrates that the extreme beaming and subdegree viewing angle of this distant blazar can account for the observed neutrino and electromagnetic activity. These findings strengthen the case for blazars as efficient accelerators of hadrons and significant contributors to the observed high-energy neutrino flux.