Search for: All records

Context.IceCube observations point to active galactic nuclei (AGNs) as promising contributors to the observed astrophysical neutrino flux. Close to the central black hole, protons can be accelerated through magnetic reconnection to very high energies and subsequently interact with abundant X-ray photons in the source, leading to neutrino production. Aims.We investigate whether the diffuse neutrino flux observed by IceCube can originate, via proton acceleration, in reconnection-powered coronae of non-jetted AGNs. Methods.We created a library of neutrino spectral templates over a large grid of values for the three key model parameters: the proton plasma magnetization of the coronaσ_p, the X-ray coronal luminosity, and the black hole mass. Synchrotron cooling of pions and muons plays a significant role due to the large coronal magnetic fields. To infer the diffuse neutrino flux, we coupled the single-source model with a mock AGN catalog consistent with the observed X-ray and mid-infrared AGN samples at redshiftsz = 0 − 4. Results.The coronal emission satisfactorily explains the most recent IceCube measurements of the diffuse neutrino flux up to energies of ∼1 PeV, provided that ∼10% of the AGN coronae haveσ_p ∼ 10⁵, while the rest are distributed over a range of lower magnetizations. Coronal emission is suppressed at higher energies by pion and muon cooling so that another population is required, with jetted AGNs being strong candidates. 

Abstract A ubiquitous feature of accreting black hole systems is their hard X-ray emission which is thought to be produced through Comptonization of soft photons by electrons and positrons in the vicinity of the black hole, in a region with optical depth of order unity. The origin and composition of this Comptonizing region, known as the corona, is a matter open for debate. In this paper we investigate the role of relativistic protons accelerated in black-hole magnetospheric current sheets for the pair enrichment and neutrino emission of AGN coronae. Our model has two free parameters, namely the proton plasma magnetizationσ_p, which controls the peak energy of the neutrino spectrum, and the Eddington ratio λ_X,Edd(defined as the ratio between X-ray luminosityL_Xand Eddington luminosityL_Edd), which controls the amount of energy transferred to secondary particles. For sources with λ_X,Edd≳ λ_Edd,crit(where λ_Edd,crit∼ 10^-1forσ_p= 10⁵or ∼ 10^-2forσ_p= 10⁷), proton-photon interactions andγγannihilation produce enough secondary pairs to achieve Thomson optical depthsτ_T∼ 0.1-10. In the opposite case of λ_X,Edd≲ λ_Edd,crit, the coronal pairs cannot originate only from hadronic interactions. Additionally, we find that the neutrino luminosity scales asL²_X/L_Eddfor λ_X,Edd≲ λ_Edd,crit, while it is proportional toL_Xfor higher λ_X,Eddvalues. We apply our model to four Seyfert galaxies, including NGC 1068, and discuss our results in light of recent IceCube observations.