arXiv subjects

D. Karavola

Publications and source records attributed to D. Karavola.

3 recordsLinked to original sources

arXiv2026

Diffuse neutrino flux from relativistic reconnection in AGN coronae

IceCube observations point to Active Galactic Nuclei (AGN) 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. We investigate whether the diffuse neutrino flux observed by IceCube can originate, via proton acceleration, in reconnection-powered coronae of non-jetted AGN. We create a library of neutrino spectral templates, over a large grid of values for the three key model parameters: the proton plasma magnetization of the corona $σ_{\rm p}$, 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. We couple the single-source model with a mock AGN catalog, consistent with the observed X-ray and mid-infrared AGN samples at redshifts $z=0-4$, to infer the diffuse neutrino flux. Coronal emission satisfactorily explains the most recent IceCube measurements of the diffuse neutrino flux up to energies of $\sim 1$~PeV, provided that $\sim$10\% of the AGN coronae have $σ_{\rm p} \sim 10^5$, 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 AGN being strong candidates.

astro-ph.HE↗

arXiv2026

Delayed Radio Flares in Neutrino-associated Blazars: The Case of TXS 0506+056

Radio flares have been postulated to be associated with the production of astrophysical neutrinos. For example, TXS 0506+056 exhibits a 2-3 yr delay between the 2017 IceCube-170922A/$γ$-ray flare and a GHz radio maximum. We quantitatively test if the delayed radio flare originates from the same compact region where neutrinos and $γ$-rays are produced as it expands downstream and synchrotron self-absorption (SSA) is reduced. Starting from the 2017 flare blob parameters, we model the expanding production region and its evolving radio emission with LeHaMoC in a fully time-dependent framework, and compare our 1.2-22 GHz light curves to RATAN-600 data. We study different scenarios with increasing levels of sophistication, including continuous injection and energy re-dissipation on pc scales. While a simple expanding blob scenario fails to reproduce the radio data, a downstream dissipation episode of particles in the optically thin regime, followed by jet deceleration, successfully describes the radio evolution. Within our one-zone time-dependent framework, the delayed radio flare is unlikely to come from an expanding neutrino production zone becoming transparent to radio emission. Additional ingredients are needed, such as re-dissipation downstream with a subsequent Doppler-factor decline. The radio flare is powered by leptonic synchrotron emission and is largely insensitive to the proton population relevant for neutrino production, implying that the delayed radio flare mainly probes downstream dissipation and beaming in certain jet configurations rather than being a genuine feature associated with the neutrino production.

astro-ph.HE↗

arXiv2026

Neutrino and pair creation in reconnection-powered coronae of accreting black holes

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 magnetization $σ_{\rm p}$, which controls the peak energy of the neutrino spectrum, and the Eddington ratio $λ_{\rm X, Edd}$ (defined as the ratio between X-ray luminosity $L_{\rm X}$ and Eddington luminosity $L_{\rm Edd}$), which controls the amount of energy transferred to secondary particles. For sources with $λ_{\rm X, Edd} \gtrsim λ_{\rm Edd, crit}$ (where $λ_{\rm Edd, crit} \sim 10^{-1}$ for $σ_{\rm p}=10^5$ or $\sim 10^{-2}$ for $σ_{\rm p}=10^7$), proton-photon interactions and $ γγ$ annihilation produce enough secondary pairs to achieve Thomson optical depths $τ_{\rm T} \sim 0.1-10$. In the opposite case of $λ_{\rm X, Edd} \lesssim λ_{\rm Edd, crit}$, the coronal pairs cannot originate only from hadronic interactions. Additionally, we find that the neutrino luminosity scales as $L^2_{\rm X}/L_{\rm Edd}$ for $λ_{\rm X, Edd} \lesssim λ_{\rm Edd, crit}$, while it is proportional to $L_{\rm X}$ for higher $λ_{\rm X, Edd}$ values. We apply our model to four Seyfert galaxies, including NGC 1068, and discuss our results in light of recent IceCube observations.

astro-ph.HE↗