On the Origin of ∼100 TeV Neutrinos from the Seyfert Galaxy NGC 7469

Abstract The origin of TeV–PeV neutrinos detected by IceCube remains largely unknown. The most significant individual neutrino source is the Seyfert galaxy NGC 1068 with a soft spectrum. Another notable candidate is the Seyfert galaxy NGC 7469, which has been recently proposed as a potential neutrino emitter. The likelihood fit of the IceCube data for this source returned a hard spectral index of ∼1.9, and the excess is dominated by two high-energy events. The energies of these two neutrinos are estimated to be 100–200 TeV, implying a maximum proton energy <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>p</mml:mi> <mml:mo>,</mml:mo> <mml:mi mathvariant="normal">max</mml:mi> </mml:mrow> </mml:msub> <mml:mo>&gt;</mml:mo> <mml:mn>2</mml:mn> <mml:mspace width="0.25em"/> <mml:mi mathvariant="normal">PeV</mml:mi> </mml:math> , significantly higher than that in NGC 1068. In this paper, we analyze the Fermi Large Area Telescope observations of NGC 7469, which yield nondetection. The size of the neutrino-emitting region can be constrained by the nondetection when the neutrino flux takes a high value in the allowed range. We suggest that cosmic-ray protons are accelerated to PeV energies via turbulence or magnetic reconnection in the corona and produce ∼100–200 TeV neutrinos via the pγ process. In the turbulence acceleration scenario, the required maximum proton energy can be achieved with a magnetization parameter of σ ∼ 1, while in the reconnection scenario, a magnetization parameter with σ ∼ 10 is needed. In both scenarios, a pair-dominated composition for the corona is preferred. The difference in the neutrino spectrum between NGC 7469 and NGC 1068 could be due to a different magnetization parameter despite the fact that they belong to the same type of active galactic nucleus.