Multimessenger tests of cosmic-ray acceleration in radiatively inefficient accretion flows

Abstract

The cores of active galactic nuclei (AGNs) have been suggested as the sources of IceCube neutrinos, and recent numerical simulations have indicated that hot AGN coronae of Seyfert galaxies and radiatively inefficient accretion flows (RIAFs) of low-luminosity AGNs (LLAGNs) may be promising sites of ion acceleration. We present detailed studies on detection prospects of high-energy multimessenger emissions from RIAFs in nearby LLAGNs. We construct a model of RIAFs that can reproduce the observational features of the current X-ray observations of nearby LLAGNs. We then calculate the high-energy particle emissions from nearby individual LLAGNs, including MeV gamma rays from thermal electrons, TeV-PeV neutrinos produced by non-thermal protons, and sub-GeV to sub-TeV gamma rays from proton-induced electromagnetic cascades. We find that, although these are beyond the reach of current facilities, proposed future experiments such as e-ASTROGAM and IceCube-Gen2 should be able to detect the MeV gamma rays and the neutrinos, respectively, or else they can place meaningful constraints on the parameter space of the model. On the other hand, the detection of high-energy gamma rays due to the electromagnetic cascades will be challenging with the current and near-future experiments, such as Fermi and Cherenkov Telescope Array. In an accompanying paper, we demonstrate that LLAGNs can be a source of the diffuse soft gamma-ray and TeV-PeV neutrino backgrounds, whereas in the present paper, we focus on the prospects for multi-messenger tests which can be applied to reveal the nature of the high-energy neutrinos and photons from LLAGNs.

Soft gamma rays from low accreting supermassive black holes and connection to energetic neutrinos

“…First, we describe the properties of the thermal plasma in RIAFs (see subsection Emission from thermal electrons in RIAFs in Methods and Ref. 29 for technical details). Thermal electrons in RIAFs emit broadband photons through synchrotron radiation, bremsstrahlung, and inverse Compton scattering.…”

“…The dotted horizontal line indicates N μ ¼ 1 for comparison. Stacking more LLAGN does not help improving the detectability because the background also increases with the number of the stacked LLAGN 29 . Fig.…”

Astronomy with energy dependent flavour ratios of extragalactic neutrinos

“…The core models of AGN are examples of the kind of astrophysical objects we are referring to. Although, the acceleration mechanism for the cosmic rays and sites for shocks are not known, for our purpose, it is safe to consider a situation in which neutrinos are produced from the charged pions originating from the interaction of accelerated protons with photons in the corona around a distance ∼ 10-40R s , where R s = 2GM BH is the Schwarzschild radius of the black hole [53][54][55].…”

Cosmic rays from the nearby starburst galaxy NGC 253: the effect of a low-luminosity active galactic nucleus

“…Moreover, recently some authors have proposed that RIAFs might play a role in the neutrino emission of LLAGNs (e.g. Kimura et al 2015Kimura et al , 2019.…”