Supernova remnants are considered major contributors to the Galactic cosmic-ray population. However, many existing numerical models of particle acceleration at the remnants shocks still rely on over-simplified geometries that cannot reproduce the rich and asymmetric emission morphologies that many remnants show on account of their interaction with their inhomogeneous surroundings.
In this...
Active Galactic Nuclei (AGN) and their relativistic jets that emit radiation covering almost the entire electromagnetic spectrum, have been few of the most fascinating subjects in astronomy for decades, yet the composition of these relativistic jets is still not clearly known. The origin of the high energy peak in the Spectral Energy Distribution (SED) of blazars has been an open question in...
The first multimessenger observation involving gravitational waves, GW170817, demonstrated the essential role of combining information from different messengers and from the entire electromagnetic spectrum to achieve a comprehensive understanding of astrophysical phenomena. In the coming years, the Cherenkov Telescope Array Observatory (CTAO) — the largest and most sensitive ground-based...
Neutron stars—pulsars—and their magnetospheres are key sources for multi-messenger astrophysics. Their emission spans the entire electromagnetic spectrum, they are strong candidates for contributing to the cosmic-ray positron excess, and theoretical models (though not yet confirmed observationally) suggest that they may also produce high-energy neutrinos in the TeV–PeV range. By combining...
The Seyfert galaxies NGC 1068 and NGC 4151 have emerged as the most promising counterparts of 4.2σ and 3.0σ neutrino excesses detected by IceCube in the TeV energy range.
Gamma rays and neutrinos are co-produced at the same flux level via hadronic interactions between the parent proton population and the ambient matter and radiation in the neutrino-emitting region. Observations of NGC 1068...
Stochastic particle acceleration in magnetized turbulent plasmas, and its resulting multi-messenger signatures, has received increased attention in recent years. A detailed modeling of this process is however made complex by the need to treat simultaneously particle acceleration and radiative processes.
We present here a hybrid numerical code that couples AM3 [1], a state-of-the-art,...
Constraining neutron-star structure requires models that are physically faithful yet fast enough for the evaluations required by Bayesian sampling. We begin with static vacuum field (SVF) magnetospheres, where direct light-curve synthesis is too slow for practical MCMC; our neural-network (NN) surrogate matches SVF profiles with high fidelity and provides ~400x speedups, enabling multipolar...
High center-of-mass electromagnetic (EM) interactions could produce decaying heavy leptons and hadrons, leading to neutrino generation. These processes might occur in the most extreme astrophysical and cosmological scenarios, potentially altering the expected gamma-ray and neutrino fluxes in both the hadronic and the leptonic pictures. For instance, neutrinos could arise from high-redshift EM...
The macroscopic structure and dynamics of relativistic AGN jets regulate where and how particles reach very high energies. Recollimation shocks—and the turbulent regions that form downstream—act as natural sites of localized dissipation and non-thermal particle acceleration. Using high-resolution 2D and 3D RMHD simulations with PLUTO, we examine how external confinement, jet–ambient pressure...
The origin of Very High-Energy (VHE) gamma-ray emission in High-frequency peaked BL Lac objects (HBLs) remains debated. While standard leptonic models successfully explain the synchrotron peak, they often struggle to reproduce hard TeV spectra without extreme parameters. We explore a hybrid scenario where the VHE emission arises from the interaction of stochastically accelerated protons with...
The super-fast (~day), very-high-energy (VHE; >0.1 TeV) photon flares from the nearby active galactic nucleus M87 provide a unique, exciting opportunity to fast-forward our understanding of particle acceleration in jets. After a long break since 2010, the Event Horizon Telescope (EHT) multiwavelength (MWL) campaign captured a new VHE flare in 2018 with unprecedented frequency coverage...
General Relativistic MagnetoHydroDynamic (GRMHD) simulations solve the time-dependent electro- and hydrodynamic partial differential equations in arbitrary spacetimes. They usually employ conservative integration routines to advance the solution in the time domain, which are known to produce mostly numerically stable results. The most common one is the Finite Volume Method, which accurately...
Sagittarius A* has been investigated for years and is one of the most interesting sources in the Galactic Center, a region enriched by strong magnetic fields, dense gas and enhanced cosmic-ray activity. The black hole’s shadow was imaged for the very first time in 2022 by the Event Horizon Telescope at a frequency of 230 GHz, demonstrating a characteristic ring morphology and a significantly...
Non-jetted AGN exhibit hard X-ray emission with a power law spectrum above $\sim$2 keV, which is thought to be produced through Comptonization of soft photons by electrons and positrons (pairs) in the vicinity of the black hole. The origin and composition of this plasma source, known as the corona, is a matter open for debate.
Our study focuses on the role of relativistic protons accelerated...
Identifying the astrophysical sources of high-energy cosmic neutrinos remains a central challenge in multi-messenger astronomy. Following the association of a 290 TeV neutrino detected by IceCube with the flaring blazar TXS 0506+056, theoretical studies have focused on modelling the photon–neutrino connection in blazars. We present a computational framework combining advanced...
In September 2017, a high-energy neutrino event detected by the IceCube Neutrino Observatory (IceCube-170922A) was associated, at the $3\sigma$ level, with a gamma-ray flare from the blazar TXS 0506+056. Cosmic rays that are accelerated in astrophysical sources can escape from their jets and interact with background radiation fields. Interactions with the extragalactic background light can...
High energy (HE) neutrinos have been observed by neutrino observatories for over a decade. Nevertheless, their origin and mechanisms responsible for their production still remain a mystery. Tidal disruption events (TDEs) have been proposed as candidate HE neutrino emitters, however a statistical association between the two has yet to be established. I will discuss results from the statistical...
We will present our efforts to obtain the reference solution for the ideal force-free 3D pulsar magnetosphere with Physics Inspired Neural Networks (PINNs). We will present our first results, we will show where and why they differ from all current state-of-the-art solutions, and we will discuss the potential of PINNs for astrophysics.
Turbulent particle acceleration is widely invoked to explain high-energy emission from extreme astrophysical sources. However, standard second-order Fermi models based on Fokker–Planck equation neglect complex non-linear effects emerging in the high-amplitude ($\delta B/B \sim 1$) and relativistic turbulence regimes, expected in many astrophysical environments. Recent MHD and PIC simulations...
The origin of high-energy neutrinos is fundamental to our understanding of the Universe. Immense effort has been put into identifying extragalactic sources of TeV-PeV neutrinos but still to no avail. Blazars has been proposed as one of the most promising candidates, however, the original association of a blazar with a high-energy neutrino has generated more questions than answers. I will...
In April 2013, the TeV blazar Mrk421 underwent one of its most powerful emission outbursts to date. An extensive multi-instrument campaign, which included MAGIC, VERITAS, and NuSTAR, provided comprehensive VHE and X-ray coverage over nine consecutive days.
In this talk I will present a detailed spectral analysis of the X-ray and VHE emissions on sub-hour timescales throughout the flare. We...
There have been recent population studies supporting the idea that radio-loud blazars can be the potential source of high-energy astrophysical neutrinos being observed by IceCube. The understanding of neutrino production from these sources is intimately connected to explaining their multi-wavelength spectra as well. In this talk, ongoing work will be presented in modelling the lepto-hadronic...
