Hard X-ray emission from blazars associated with high-energy neutrinos

A. V. Plavin, R. A. Burenin, Y. Y. Kovalev, A. A. Lutovinov, A. A. Starobinsky, S. V. Troitsky, E. I. Zakharov

Published 2023-06-01Version 1

Bright blazars were found to be prominent neutrino sources, and a number of IceCube events were associated with them. Evaluating high-energy photon emission of such blazars is crucial for better understanding of the processes and regions where neutrinos are produced. Here, we focus on hard X-ray emission observed by the SRG/ART-XC telescope, by the Swift/BAT imager, and by the INTEGRAL/IBIS telescope. Their energy range ~10 keV and above is well-suited for probing photons that potentially participate in neutrino production by interacting with ultrarelativistic protons. We find that neutrino-associated blazars tend to demonstrate remarkably strong X-ray emission compared to other VLBI blazars in the sky, chance coincidence probability is p=0.5%. Both neutrinos and hard X-rays are found to come from blazars at cosmological distances z ~ 1, and are boosted by relativistic beaming that makes it possible to detect them on Earth. Our results suggest that neutrinos are produced within compact blazar jets, with target X-ray photons emitted from accelerated jet regions.