A Seyfert galaxy as a hidden counterpart to a neutrino-associated blazar

TL;DR

This study investigates the potential link between high-energy neutrinos and active galactic nuclei, revealing that a Seyfert galaxy may be a significant, previously overlooked contributor to neutrino hotspots, challenging prior assumptions about blazar dominance.

Contribution

The paper presents new NuSTAR observations showing a Seyfert galaxy as a plausible counterpart to a neutrino hotspot, highlighting the importance of considering multiple AGN sources in multimessenger astronomy.

Findings

NGC 5610's hard X-ray flux exceeds that of the blazar PKS 1424+240.

Both AGN align with the X-ray-neutrino correlation when flux is apportioned.

IceCube hotspots may be unresolved blends of multiple AGN.

Abstract

The origin and production mechanisms of high-energy astrophysical neutrinos remain open questions in multimessenger astronomy. Previous studies have hinted at a possible linear correlation between the hard X-ray and high-energy neutrino emission in active galactic nuclei. New \textit{NuSTAR} observations, first presented here, reveal that blazar PKS 1424+240, located within a prominent IceCube neutrino hotspot, is far fainter in hard X-rays than expected from this trend. Motivated by this apparent ambiguity, we identify the nearby Seyfert galaxy NGC 5610, also coincident with the hotspot, whose unabsorbed hard X-ray flux exceeds that of PKS 1424+240 by about an order of magnitude. When the local IceCube neutrino flux is apportioned between the two AGN in proportion to their hard X-ray emission, both align with the previously suggested X-ray-neutrino correlation. This suggests that certain IceCube hotspots may be unresolved blends of multiple AGN, and supports a multimessenger scenario in which high-energy neutrinos and hard X-rays originate from the same hadronic interactions, with the X-ray emission produced through cascade reprocessing.