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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 magnetizationσp, which controls the peak energy of the neutrino spectrum, and the Eddington ratio λX,Edd(defined as the ratio between X-ray luminosityLXand Eddington luminosityLEdd), which controls the amount of energy transferred to secondary particles. For sources with λX,Edd≳ λEdd,crit(where λEdd,crit∼ 10-1forσp= 105or ∼ 10-2forσp= 107), proton-photon interactions andγγannihilation produce enough secondary pairs to achieve Thomson optical depthsτT∼ 0.1-10. In the opposite case of λX,Edd≲ λEdd,crit, the coronal pairs cannot originate only from hadronic interactions. Additionally, we find that the neutrino luminosity scales asL2X/LEddfor λX,Edd≲ λEdd,crit, while it is proportional toLXfor higher λX,Eddvalues. We apply our model to four Seyfert galaxies, including NGC 1068, and discuss our results in light of recent IceCube observations.
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This content will become publicly available on December 1, 2025
The role of magnetospheric current sheets in pair enrichment and ultra-high energy proton acceleration in M87*
Abstract Recent advances in numerical simulations of magnetically arrested accretion onto supermassive black holes have shed light on the formation and dynamics of magnetospheric current sheets near the black hole horizon. By considering the pair magnetizationσein the upstream region and the mass accretion rateṁ(in units of the Eddington mass accretion rate) as free parameters we estimate the strength of the magnetic field and develop analytical models, motivated by recent three-dimensional particle-in-cell simulations, to describe the populations of relativistic electrons and positrons (pairs) in the reconnection region.Applying our model to M87*, we numerically compute the non-thermal photon spectra for various values ofσe. We show that pairs that are accelerated up to the synchrotron radiation-limited energy while meandering across both sides of the current sheet, can produce MeV flares with luminosity of ∼ 1041 erg s-1— independent ofσe— for a black hole accreting atṁ=10-5. Pairs that are trapped in the transient current sheet can produce X-ray counterparts to the MeV flares, lasting about a day for current sheets with length of a few gravitational radii. We also show that the upstream plasma can be enriched due to photon-photon pair creation, and derive a new equilibrium magnetization ofσe∼ 103-104forṁ= 10-6- 10-5. Additionally, we explore the potential of magnetospheric current sheets to accelerate protons to ultra-high energies, finding that while acceleration to such energies is limited by various loss mechanisms, such as synchrotron and photopion losses from the non-thermal emission from pairs, maximal proton energies in the range of a few EeV are attainable in magnetospheric sheets forming around supermassive sub-Eddington accreting black holes.
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- PAR ID:
- 10561342
- Publisher / Repository:
- JCAP
- Date Published:
- Journal Name:
- Journal of Cosmology and Astroparticle Physics
- Volume:
- 2024
- Issue:
- 12
- ISSN:
- 1475-7516
- Page Range / eLocation ID:
- 009
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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