arXiv subjects

Federico Testagrossa

Publications and source records attributed to Federico Testagrossa.

6 recordsLinked to original sources

arXiv2026

Neutrinos and gamma rays from Seyfert galaxies constrain the properties of coronal turbulence

The TeV neutrino signal observed by IceCube from the active galactic nucleus (AGN) NGC 1068 can probe its innermost coronal regions. If these neutrinos originate from hadrons accelerated within a magnetized turbulent corona, their intensity and spectrum depend on the turbulent magnetic field strength and turbulence coherence scale. The gamma rays accompanying neutrino production are absorbed in this optically thick environment, in a way that depends sensitively on the size of the corona. By a joint fit of the IceCube and Fermi-LAT observations, we translate the multimessenger signal from NGC 1068 and the tentative signal from NGC 7469 into quantitative constraints on coronal properties. NGC 1068, with a significant TeV neutrino excess, favors a compact, strongly magnetized corona with a large turbulence coherence length relative to the coronal size. NGC 7469, with two $\sim 100$ TeV neutrino events, points instead to a somewhat larger corona with much smaller coherence length and high magnetization, but a very small fraction of energy in non-thermal protons. We obtain the diffuse flux from a population of Seyfert galaxies identical to either NGC 1068 or NGC 7469. Finally, we consider a third scenario, motivated by the spectral break observed in the diffuse neutrino flux at tens of TeV, with coronal properties intermediate between the two point-source-inspired models. To enable detailed comparisons with the IceCube and electromagnetic observations, we release our model predictions in a GitHub repository.

astro-ph.HE↗

arXiv2025

Accelerating SED Modeling of Astrophysical Objects Using Neural Networks

Interpreting the spectral energy distributions (SEDs) of astrophysical objects with physically motivated models is computationally expensive. These models require solving coupled differential equations in high-dimensional parameter spaces, making traditional fitting techniques such as Markov Chain Monte Carlo or nested sampling prohibitive. A key example is modeling non-thermal emission from blazar jets - relativistic outflows from supermassive black holes in Active Galactic Nuclei that are among the most powerful emitters in the Universe. To address this challenge, we employ machine learning to accelerate SED evaluations, enabling efficient Bayesian inference. We generate a large sample of lepto-hadronic blazar emission models and train a neural network (NN) to predict the photon spectrum with strongly reduced run time while preserving accuracy. As a proof of concept, we present an NN-based tool for blazar SED modeling, laying the groundwork for future extensions and for providing an open-access resource for the astrophysics community.

astro-ph.HE↗

arXiv2025

A generalized study of linear electromagnetic cascades in astrophysical sources

High-energy gamma rays can trigger electromagnetic cascades via pair production on ambient photons, reprocessing their energy to lower frequencies. A classic example is the cascade from the gamma rays produced by ultra-high-energy cosmic rays in extragalactic photon fields, whose universal spectral shape was first described by Berezinsky in the 1970s. Recently, internal cascades, developing within the gamma-ray sources themselves, have gained a prominent role, as the IceCube data suggest that most detected neutrinos originate in gamma-ray-opaque environments. We analyze under what conditions these internal cascades can approach a universal spectrum. Since the Berezinsky treatment breaks down if synchrotron losses dominate, we present a generalized theory incorporating synchrotron-dominated cascades. We show the emergence of universal cascade spectrum among various examples of high-energy sources containing non-thermal cosmic rays, and discuss the conditions for its appearance.

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arXiv2025

An Accretion Flare Interpretation for the Ultra-High-Energy Neutrino Event KM3-230213A

We study the origin of the ultra-high-energy (UHE) neutrino event KM3-230213A detected by KM3NeT, focusing on MRC 0614-083 which has been pinpointed as the closest blazar to the neutrino localization exhibiting variable multi-wavelength emission. A joint interpretation of the optical, infrared, and X-ray light curves suggests that MRC 0614-083 has undergone a super-Eddington accretion flare accompanied by efficient proton acceleration. That flare has initiated a delayed infrared echo within the surrounding dust torus, which serves as a target for photomeson ($p\gamma$) interactions such that a self-consistent picture emerges that complements the blazar jet scenario: the predicted UHE neutrino flux is at the level expected from joint $E^{-2}$ fit with the IceCube measurements at lower energies, the variable nature of the event alleviates the tension with IceCube limits, and the accompanying electromagnetic cascade describes the X-ray flare around the neutrino detection time. Since a key remaining uncertainty is the unknown redshift of the source, we strongly encourage optical/ultraviolet spectroscopic measurements to determine its redshift.

astro-ph.HE↗

arXiv2025

Can the neutrinos from TXS 0506+056 have a coronal origin?

The blazar TXS 0506+056 has been the first astrophysical source associated with high-energy astrophysical neutrinos, and it has emerged as the second-most-prominent hotspot in the neutrino sky over ten years of observations. Although neutrino production in blazars has traditionally been attributed to processes in the powerful relativistic jet, the observation of a significant neutrino flux from NGC 1068 -- presumably coming from the Active Galactic Nucleus (AGN) corona -- suggests that neutrinos can also be produced in the cores of AGN. This raises the question whether neutrino production in TXS~0506+056 is also associated with the core region. We study this scenario, focusing on the hypothesis that this blazar is a masquerading BL Lac, a high-excitation quasar with hidden broad emission lines and a standard accretion disk. We show that magnetic reconnection is an acceleration process necessary to reach tens of PeV proton energies, and we use observationally motivated estimates of the X-ray luminosity of the coronal region to predict the emission of secondaries and compare them to the observed multi-wavelength and neutrino spectra of the source. We find that the coronal neutrino emission from TXS 0506+056 is too low to describe the IceCube observed neutrinos from this AGN, which in turn suggests that the blazar jet remains the preferred location for neutrino production.

astro-ph.HE↗

arXiv2023

Two-detector flavor sensitivity to ultra-high-energy cosmic neutrinos

Ultra-high-energy (UHE) cosmic neutrinos, with energies above 100 PeV, could be finally discovered in the near future. Measuring their flavor composition would reveal information about their production and propagation, but new techniques are needed for UHE neutrino telescopes to have the capabilities to do it. We address this by proposing a new way to measure the UHE neutrino flavor composition that does not rely on individual telescopes having flavor-identification capabilities. We manufacture flavor sensitivity from the joint detection by one telescope sensitive to all flavors -- the radio array of IceCube-Gen2 -- and one mostly sensitive to $\nu_\tau$ -- GRAND. From this limited flavor sensitivity, predominantly to $\nu_\tau$, and even under conservative choices of neutrino flux and detector size, we extract important insight. For astrophysics, we forecast meaningful constraints on the neutrino production mechanism; for fundamental physics, vastly improved constraints on Lorentz-invariance violation. These are the first measurement forecasts of the UHE $\nu_\tau$ content.

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