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arXiv · 2504.09287

Looking into the Jet Cone of the Neutrino-Associated Very High Energy Blazar PKS 1424+240

Y. Y. Kovalev·A. B. Pushkarev·J. L. Gomez·D. C. Homan·M. L. Lister·J. D. Livingston·I. N. Pashchenko·A. V. Plavin·T. Savolainen·S. V. Troitsky
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Abstract

The acceleration process of massive particles as well as the production of very high energy (VHE) photons and neutrinos remains a fundamental challenge in astrophysics. We investigate the parsec-scale jet structure and magnetic field of the blazar PKS 1424+240, that has been selected on the basis of strong VHE gamma-ray emission and identified with one of the highest peaks in the IceCube 9-year neutrino sky. We analyze 15 GHz VLBA observations of this BL Lac object, stacking 42 polarization-sensitive images collected in 2009-2025 to enhance the signal and reveal persistent parsec-scale structure. Our observations uncover a rare scenario. The object is viewed inside the jet cone, very close to the axis of its relativistic jet, with a viewing angle of <0.6 deg. This effectively maximizes Doppler boosting to values ~30 and enhances both electromagnetic and neutrino emission in the observer's direction. Based on polarimetric observations, we unambiguously detect a net toroidal component of the jet's magnetic field, indicating a current carrying jet flowing almost directly towards our line of sight. Blazars with very small jet viewing angles offer a solution to the longstanding mismatch between Doppler factors inferred from low VLBI apparent jet speed and those derived from VHE observations -- the so-called "Doppler factor crisis". We show that relativistic beaming plays the critical role in the gamma-ray and neutrino emission of blazars, with direct implications for models of their multi-messenger emission.

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Y. Y. Kovalev, A. B. Pushkarev, J. L. Gomez, D. C. Homan, M. L. Lister, J. D. Livingston, I. N. Pashchenko, A. V. Plavin, T. Savolainen, S. V. Troitsky. 2025-07-11. Looking into the Jet Cone of the Neutrino-Associated Very High Energy Blazar PKS 1424+240. https://doi.org/10.1051/0004-6361%2F202555400

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