The underlying particle acceleration mechanism in blazars and the radiation mechanism of the blazar high-energy spectral component are still not well understood. Multi-wavelength polarization signatures can provide unique constraints on the blazar radiation and plasma physics. This talk aims to emphasize the need of the multi-zone picture for the blazar leptonic and hadronic models. Under such...
I will show that current mm-to-X-ray polarization trends, observed during recent IXPE campaigns for HBLs, and the ROBOPOL trend for Fermi blazars, relating the fractional polarization to the peak frequency of the synchrotron emission, can be successfully reproduced by a multi-zone scenario without the need for an energy-stratified scenario. I will also discuss some implications for the...
Recent advancements in gamma-ray observations and theoretical modeling are transforming our understanding of relativistic jets across scales, from black hole X-ray binaries (BHXBs) to active galactic nuclei (AGN). Jets are efficient cosmic ray (CR) accelerators to PeV energies, contributing to the diffuse gamma-ray and neutrino fluxes. In BHXBs, jets persist even during quiescence, like the...
I discuss recent results of a leptohadronic model applied to a sample of 32 BL Lac objects associated with IceCube high-energy alert events. The model is constrained using multi-wavelength observations as well as optical spectral analyses, which provide valuable information on the source environment. For masquerading BL Lacs, including TXS 0506+056, the model predicts high neutrino fluxes,...
Recent multi-wavelength observations of gamma-ray burst afterglows observed in the TeV energy range challenge the simplest Synchrotron Self-Compton (SSC) interpretation of this emission and are consistent with a single power-law component spanning over eight orders of magnitude in energy. To interpret this generic behaviour in the single-zone approximation without adding further free...
Four tidal disruption events—Sw J1644, Sw J1112, Sw J2058, and AT 2022cmc—have been identified as exhibiting luminous jets accompanied by rapidly declining non-thermal X-ray emissions. In this talk, I will discuss our recent work on modeling the multi-wavelength emissions from the jetted TDE AT2022cmc, where a two-component jet is considered to interpret the spectral and temporal signatures of...
The blazar TXS 0506+056 was the first astrophysical source to be associated with high-energy neutrinos, both temporally and spatially. This breakthrough followed the detection of a high-energy neutrino coincident with the blazar’s 2017 multi-wavelength flare. Additionally, IceCube has identified TXS 0506+056 as the second most prominent hotspot in the neutrino sky over 9.5 years of...
X-ray observations are essential for understanding the emission mechanisms of active galactic nuclei (AGN), particularly blazars, whose X-ray emission predominantly follow a power-law model originating from relativistic jets oriented toward Earth. In this study, we present a detailed analysis of the candidate neutrino-emitting blazar 5BZB J0630-2406, which has been observed over multiple...
IceCube has recently discovered a neutrino diffuse emission from the Galactic Plane up to the PeV.
The spectrum of that emission is significantly higher and harder than expected to be generated by the cosmic ray (CR) population of the Galaxy if that is computed using conventional transport models.
Rather it is in good agreement with the KRA$_\gamma$ model adopting spatial dependent...
Recent observations highlight the importance of active galactic nuclei (AGN) in the context of high-energy neutrino production.
The focus of this study is 5BZB J1150+2417, which was recently proposed as associated with neutrino emission during the first $9$-yrs of IceCube observations among other blazar-type sources.
To test the proposed neutrino-blazar association we perform a...
I will discuss recent advancements in AGNpy, a Python library designed for modeling radiative processes in Active Galactic Nuclei (AGNs). I will highlight several enhancements, including preparation for incorporating time-dependent modeling to better integrate energy loss mechanisms. Additionally, I will explore a multi-layer structure for the Broad-Line Region to improve modeling accuracy for...
Multimessenger astrophysics relies on multiple observational data channels, necessitating efficient methods for analyzing events of astrophysical origin. With the continuous increase in both volume and complexity of data from modern observatories, advanced Machine Learning techniques have become very useful for identifying and classifying signals effectively.
My project aim at developing a...
The Fermi-LAT detected more than 7000 $\gamma$-ray sources in 14 years of operation which are collected in 4FGL-DR4 catalog. About a third of these sources are still unassociated with counterparts in other wavelengths and approximately one-fifth are associated with blazar of unknown type, but their classification as either BL Lac type blazars (BLL) or Flat Spectrum Radio Quasars (FSRQ) is...
The extreme high-energy synchrotron peaked (EHSP) blazars represent a subclass of these sources which emit in the very high-energy (VHE) γ-ray band. The energy of EHSPs synchrotron peak is the highest among the blazars, and usually exceeds 10^17 Hz. These sources are often known as “extreme blazars” and are particularly relevant for high-energy astrophysics since they may emit high-energy...
Following IceCube’s identification of the blazar TXS 0506+056 as the first cosmic neutrino source candidate, blazars have emerged as some of the most promising neutrino source classes. This research area is set to advance significantly with the advent of next-generation neutrino telescopes like KM3NeT/ARCA, a deep-sea Cherenkov neutrino telescope currently under construction in the...
High-energy cosmic rays are a significant aspect of the high-energy universe, but their origins and acceleration mechanisms are not fully understood. Neutrinos, generated through interactions of these cosmic rays, provide a unique means to study these energetic particles and their sources. This presentation focuses on how observations of neutrinos can inform our understanding of cosmic ray...
To identify the sources of cosmic-rays, and characterize their astrophysical properties we need to exploit the full potential of multi-messenger observations in combination with theoretical models. We aim to ease the theoretical interpretation of multi-messenger datasets by providing to the community a minimization tool using the open-source Python package Gammapy.
For this purpose,...
Blazar jets are prolific sources of high energy electromagnetic radiation but their emission region, the “blazar zone”, is uncertain because of the inherent limitation of our head-on view of the jets. Emission models vary in both the acceleration mechanism powering the blazar zone and the latter’s extent and location. Here we have adopted a model of magnetic reconnection that drives continuous...
We investigate ultra-fast outflows (UFOs) in active galactic nuclei (AGN) as potential sources of ultra-high-energy cosmic rays (UHECRs), focusing on cosmic-ray nuclei, an aspect not explored previously. These large-scale, mildly-relativistic outflows are a common feature of AGN. We study the cosmic-ray spectrum and maximum energy attainable in these environments with 3D CRPropa simulations...
The detection by the KM3NeT experiment of the ultra-high-energy event KM3-230213A is a milestone in neutrino astrophysics. With an energy estimated at ~220 PeV, it is the most energetic neutrino observed to date, challenging the current understanding of the cosmic spectrum. Its observation opens the question of its astrophysical origin. Blazars and their relativistic jets have been proposed as...
In the presentation, I will discuss the results of a comprehensive
multi-wavelength investigation of gamma-ray-bright BL Lac objects, utilizing data from the Fermi Large Area Telescope (LAT) and the Swift Observatory (XRT and UVOT) to analyze spectral energy distributions (SEDs) and temporal characteristics of these sources. The research focuses on a sample of bright and highly variable BL...
The low-luminosity radio galaxy NGC 4278, with parsec-scale jets, was recently identified as a TeV source by the LHAASO collaboration during the 2020-2021 campaign. It is the first of its class detected above 100 GeV, challenging current models of particle acceleration in low-power radio galaxies.
In this contribution, we present the analysis of the LAT data in the region of 1LHAASO...
The interactions of ultra-high energy cosmic ray nuclei (UHECR) in astrophysical scenarios can be of stochastic or deterministic nature. Simulation frameworks often employ Monte Carlo techniques or numerically solve systems of ordinary differential equations (ODEs) to describe such interactions and the resulting nuclear cascades. Monte Carlo approaches are best suited to asses the impact of...
GAMERA is an open-source software package for modelling non-thermal ra-
diation processes. It has been used in various publications to model the time
evolution of populations of leptonic and hadronic cosmic rays in constant and
changing environments and to compute the resulting photon and secondary par-
ticle spectra. While the core is written in C++ to allow fast computations, a
Python...
We will present developments towards the DIPLODOCUS code (Distribution In PLateaux methodOLOgy for the Computation of Boltzmann eqUationS), written from scratch using the Julia coding language, and designed to kinetically model dynamics and emissions from AGN jets and other jetted sources. The code expands on the concept of multi-zone jet models to include anisotropic distributions in momentum...
We use PLUTO (Mignone et al., 2007) relativistic hydrodynamics (RHD) simulations to connect information about electron energy spectra to the ages and fuelling processes of active galactic nuclei (AGN). We adapt the Lagrangian particle module (Vaidya et al, 2018 and Mukherjee et al, 2021) to model emission from RHD simulations without explicitly evolving the magnetic fields. We further adapt...
We present a theoretical model for detecting axions from neutrons stars in a QCD phase of quark matter. The axions would be produced from a quark-antiquark pair $u\bar{u}$ or $d\bar{d}$, in loop(s) involving gluons. The chiral anomaly of QCD and the spontaneously broken symmetry are invoked to explain the non-conservation of the axion current. From the coupling form factors, the axion...
Black hole-neutron star (NSBH) coalescence events are regarded as highly significant phenomena within the current multimessenger framework of gravitational waves,
and they are poised to assume an increasingly prominent role in the foreseeable future. To date, only a handful of such events have been observed,
with GW200105 and GW200115 being the most noteworthy among them. However, with the...
I will present progress on the development of the radiation module of cuHARM, a finite volume code which solves the general relativistic radiation magnetohydrodynamic equations in curved space-time. The specific intensity is resolved in frequency and in direction on a geodesic grid. I will describe the challenges linked to this discretization, which does not rely on the widely used M1 or M2...
The electromagnetic flare of the flat-spectrum radio quasar (FSRQ) 3C 454.3 in November 2010 was the brightest $\gamma$-ray flare ever observed by the Fermi-LAT from a blazar. We performed the data analysis of the multiwavelength (from infrared photons to $\gamma$ rays) quasi-simultaneous one-day-averaged spectral-energy distributions (SEDs) for seven days of the flare and modelled the...
Blazars are a subclass of Active Galactic Nuclei (AGN) powered by the accretion of matter to a supermassive black hole (SMBH). Charged particles can be accelerated in the jets produced near the SMBH and produce non-thermal radiation relativistically boosted in the observer's frame. Recently a high-energy neutrino has been detected from the direction of a distant blazar known as TXS 0506+056,...
Blazars are luminous astrophysical objects that show a high variability in brightness. They emit powerful relativistic jets which are aligned with the observer's line of sight. The broad emission from radio up to gamma rays can be explained by interactions of non-thermal particles in the jet. Nonetheless, the origin of the high-energy emission of blazars is still not clear. Various theoretical...
This talk will discuss recent work on the connection between blazar flares and high-energy astrophysical neutrinos. Using the time-dependent lepto-hadronic code OneHaLe, we analysed the spectral energy distributions and light curves of several bright γ-ray flares observed by the Fermi Large Area Telescope. The results indicate that the calorimetric estimates for neutrino production rates...
Rapid flux variability over a large range of wavelengths is a well-known signature of emission from blazars, with variability time scales of the order of a few days and below frequently observed at high energies.
Different radiative models with varying degrees of complexity are being developed to either reproduce individual flare events or overall statistical behaviour, but a general picture...
Supermassive black holes reside in the center of galaxies and are characterised that not even light can escape their gravitational pull.
However, in their direct vicinity high-energies flares occur, particles are accelerated to highest energies and relativistic outflows are launched.
In order to understand these phenomena we perform GRMHD simulations of accreting black holes taking magnetic...
