Blazar PKS 0446+11—Neutrino Connection Study Using a Lepto-hadronic Model

Abstract We present a multiwavelength study of blazar PKS 0446+11, motivated by its spatial association with the neutrino event IC 240105A detected by the IceCube Neutrino Observatory on 2024 January 5. The source is located 0 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>.</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>°</mml:mi> </mml:mrow> </mml:mover> </mml:math> 4 from the best-fit neutrino direction and satisfies selection criteria for very long baseline interferometry–selected, radio-bright active galactic nuclei that have been identified as highly probable neutrino associations. PKS 0446+11 exhibited a major γ -ray flare in 2023 November, reaching ∼18​​​​​​× its 4FGL-DR4 catalog average. Around the neutrino epoch, PKS 0446+11 remained in an elevated state, with the γ -ray flux more than 6 times above its catalog level, the X-ray flux an order of magnitude above the archival measurements, and the optical-UV emission also enhanced. We used Fermi-LAT, Swift-XRT/UVOT, and archival multiwavelength data to construct multiwavelength light curves and spectral energy distributions (SEDs). SED modeling shows that the emission is best described by a leptonic scenario, with synchrotron emission at low energies and external Compton scattering of broad-line region and dusty torus photons dominating the X-ray– γ -ray output. A lepto-hadronic model fails to adequately reproduce the observed SED, although hadronic cascades can broadly account for the X-ray and γ -ray spectral coverage at lower flux levels. We compute the expected neutrino flux for the hadronic scenario and compare it to the IceCube 90% upper limit. Our results highlight the importance of continued multiwavelength and neutrino monitoring to better understand the physical conditions under which this blazar may serve as a neutrino source.