Workshop on Numerical Multi Messenger Modeling

26 Feb 2025, 08:45 → 28 Feb 2025, 15:00 Europe/Berlin

Building C, Seminar Room CTAO (DESY)

^{Copyright: DESY/ Science Communication LAB}

The workshop aims at bringing together the community working on numerical codes to simulate multi-messenger (photon/neutrino/cosmic-ray) emission from astrophysical sources.

It is a third meeting of this kind: 

• 2024, APC https://indico.in2p3.fr/event/31722/
• 2023, Bochum https://indico.uni-wuppertal.de/event/230/

The workshop will allow for extensive time for discussion and co-working. The main topics addressed are: 

• news from code developments and code comparison
• applications to hot sources in the photon/neutrino sky
• multi-messenger fitting

 

02_Gruppenfoto.jpg

Hotelliste-2024_SN.pdf

Zeuthen-Plan-2024-09_mit Legende.pdf

Wednesday 26 February

Session 1

1 Welcoming session

Speaker: Walter Winter (Z_THAT (Theoretische Astroteilchenphysik))

2502_NumericalModeling_DESY.pdf

2 Multi-wavelength polarization signatures of jets

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 a scenario, the polarization degree of the blazar high-energy spectral component from leptonic and hadronic models can be drastically different from the one-zone picture. Specifically, the leptonic polarization is mostly undetectable by IXPE and future X-ray and gamma-ray polarimeters such as COSI. Thus any detection of polarization in the high-energy spectral component is strong evidence for hadronic models. Non-detection, however, cannot rule out hadronic models. In addition, we perform integrated particle-in-cell and polarized radiation transfer simulations to characterize multi-wavelength radiation and polarization signatures from magnetic reconnection and turbulence scenarios. Our results suggest that reconnection in a partially turbulent blazar jet can best explain the multi-wavelength polarization signatures in high-synchrotron-peaked blazars reported by IXPE.

Speaker: Haocheng Zhang (University of Maryland Baltimore County/NASA Goddard Space Flight Center)

DESY.pdf.pptx

3 On the multi-zone Synchrotron polarization of blazars

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 statistical properties of the polarization angle and for the underlying acceleration processes.

Speaker: Andrea Tramacere (Astronomy Department of the University of Geneva)

4 Jet modeling: from X-ray binaries to dark matter nature

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 case of A0620–00, suggesting their contribution to Galactic PeVatrons has been underestimated, particularly after the recent results of LHAASO on TeV emission from BHXBs. Additionally, AGN jets reveal complex interactions between CR and their environments, producing multiwavelength (MW) emission through leptonic and hadronic processes. In this talk, I will present a unified framework for modeling jet systems using an extended version of the BHJet model. By advancing its computational capabilities, this model bridges the gap between small-scale BHXB jets and large-scale AGN jets, incorporating the effects of interactions with light dark matter. Applying BHJet to A0620–00 highlights the potential cumulative gamma-ray and X-ray contributions of the BHXB population, with implications for their detectability with future observatories like CTA. For AGN, BHJet captures the steady-state MW emission accounting for the elastic scattering between CRs and light DM particles. This analysis not only deepens our understanding of jet physics but also offers insights into the potential dark matter signatures in jet environments, advancing the study of astrophysical PeVatrons and their role in fundamental physics.

Speaker: Dimitrios Kantzas (LAPTh/CNRS)

NMMM25_Kantzas.pdf

10:45 Coffee Break

Session 1

5 Modeling an IceCube blazar candidate sample with AM3

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, which can describe well the ten-year IceCube point source flux, and which strongly correlates with the gamma-ray flux. I discuss some physical insights brought by the results and implications for next-generation neutrino searches.

Speaker: Xavier Rodrigues (European Southern Observatory (ESO))

DESY2025_rodrigues.pdf

6 AM³ and lepto-hadronic gamma-ray burst afterglow spectra up to TeV energies

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 parameters, we performed an exhaustive parameter space study using the public, time-dependent, multi-messenger transport software AM³. This description accounts for the radiation from non-thermal protons and the lepto-hadronic cascade induced by $pp$- and $p{\gamma}$-interactions. In this talk, I will first introduce AM³ and give an update about recent code developments on behalf of the AM³ team. Then, I will summarise the main afterglow scenarios which we have found (SSC, Extended-syn, Proton-syn, $pp$-cascade, and $p{\gamma}$-cascade), and discuss their advantages and limitations in the multi-messenger context.

Speaker: Marc Klinger (Anton Pannekoek Institute - University of Amsterdam)

Klinger_LepHadGRBAG_AM3.pdf

7 Modeling radio and X-ray afterglows of jetted TDEs

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 AT2022cmc. I will demonstrate that the X-ray spectra and fast-decaying light curves extending up to 400 days post-disruption can be well explained by electron synchrotron emission from the fast jet’s reverse shock, while the radio observations could be attributed to slow jet forward shocks. The talk will also cover the application of the reverse shock model to interpret the X-ray afterglows from all four aforementioned jetted TDEs, as well as their gamma-ray and neutrino detectability.

Speaker: Chengchao Yuan (Z_THAT (Theoretische Astroteilchenphysik))

NMM_workshop_CY.pdf

12:45 Lunch

Co-Working

co-working session.pdf

Session 2

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

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 observations, hinting at a steady neutrino emission from the blazar. Traditionally, neutrino production in blazars has been attributed to processes occurring in the powerful relativistic jet. However, recent studies propose that neutrinos from blazars may instead originate in a core region near the supermassive black hole, such as the AGN corona or the inner accretion flow. In this contribution, we explore this alternative scenario, focusing on the hypothesis that TXS 0506+056 is a masquerading BL Lac – a high-excitation quasar with hidden broad emission lines and a standard accretion disk. Using observationally informed estimates of the X-ray luminosity of the coronal region, we predict the neutrino and electromagnetic spectra expected from a putative corona and assess their consistency with the observed multi-wavelength spectrum of the source.

Speaker: Damiano Francesco Giuseppe Fiorillo (Z_THAT (Theoretische Astroteilchenphysik))

SlidesTXS0506.pdf

9 X-Ray Spectral Features and Neutrino Production in Blazar 5BZB J0630-2406

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 epochs with XMM-Newton, NuSTAR, Swift-XRT, and eROSITA. Our findings reveal that 5BZB J0630-2406 exhibits characteristics of an X-ray "changing-look" AGN, a phenomenon more typically associated with Seyfert galaxies. Analysis of the X-ray spectra in the $2.0-10.0$ keV band shows significant variability, with high flux states adhering to the expected power-law model indicative of jet emission. However, in low-flux states, the spectrum includes an additional component consistent with corona emission, photoionised absorption, or reflection processes usually observed in obscured AGN. Notably, a spectral break observed during these low states may arise from interactions in the black hole environment, potentially linked to processes producing neutrinos. We tested a range of spectral models to investigate this spectral transition, suggesting that the emission evolves between jet-dominated and multi-component states linked to the central engine of the blazar. The identification of 5BZB J0630-2406 as an X-ray changing-look blazar, combined with its potential for neutrino production, opens new perspectives in multi-messenger astrophysics, underscoring the importance of continued multi-epoch and multi-instrument monitoring to capture the full dynamism of blazars.

Speaker: Jose Maria Sanchez Zaballa (Z_GA (Gammaastronomie))

DESY2025_jmsz.pdf

10 Consistent modelling of the neutrino and gamma-ray Galactic diffuse emissions

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 diffusion.
We show that an upgraded version of that model — accounting for KASCADE CR data up to tens of PeVs — consistently reproduces the energy spectrum and the angular distribution of the $\gamma$-ray diffuse emission recently measured by LHAASO from 1 TeV to 1 PeV.

Speaker: Dario Grasso (INFN, Pisa)

Grasso_Galactic_Diffuse.pdf

11 Lepto-hadronic modelling of neutrino-candidate blazar 5BZB J1150+2417

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 theoretical modelling study of radiative processes.
Modelling the quasi-simultaneous, broad-band spectral energy distributions, we test various methods from purely leptonic to lepto-hadronic models with external photon fields to fit the observations.
Historically, 5BZB J1150+2417 is classified as a BL Lac source.
However, our results find a spectral shape in the $\gamma-$ray emission, that suggests a deviation from the log-parabolic double hump structure, typical for these objects.
Our lepto-hadronic models predict a low neutrino production rate, although at reach of the IceCube neutrino detector over 10 years.

Speaker: Leonard Pfeiffer (Julius-Maximilians-Universität Würzburg)

Workshop_DESY_26022025_pfeiffer.pdf

12 Next Steps for AGNpy

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 Flat Spectrum Radio Quasars (FSRQs). I will also touch upon hadronic processes implemented in agnpy, such as proton synchrotron and p-gamma interactions. Furthermore, I will review the last community's usage of agnpy. Finally, I will outline future development plans for AGNpy.

Speaker: Pawel Gliwny (University of Lodz)

agnpy_berlin.pdf

Poster session

13 Anomaly Detection with Machine Learning in Time Series Data from the Fermi Anti-Coincidence Detector

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 framework using Machine Learning techniques to analyze time series data. The use case that will be presented regards the data from the Anti-Coincidence Detector (ACD) onboard the Fermi Gamma-ray Space Telescope. The primary objective is to enhance the detection of high-energy transient events, such as Gamma-Ray Bursts (GRBs) and other astrophysical signals.
An ensamble of Neural Networks models may be employed to model and predict the temporal structure of the ACD background data. The network's predictions serve as a baseline for implementing a triggering algorithm designed for anomaly detection. By identifying significant deviations from the predicted background, the system effectively flags potential astrophysical transients in the ACD time series data.

In addressing challenges such as noise variability, this work explores advanced approaches to refine anomaly detection thresholds, by characterizing the noise amplitude in the data. Bayesian Neural Networks (BNNs) are highlighted as a promising method to dynamically adapt thresholds based on the noise characteristics of the data, offering a robust alternative to traditional fixed-threshold methods. These developments demonstrate a robust and adaptable framework for signal detection, applicable across various datasets and observatories in multimessenger astrophysics.

Speaker: Andrea Adelfio (INFN - Sezione Perugia)

Poster url

14 Artificial neural network classification of the Fermi-LAT catalog blazars of unknown type and unidentified sources

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 still unclear. Among the sources in 4FGL-DR4 catalog, most have incomplete spectra. For the classification of the 4FGL-DR4 catalog unidentified sources (UID) and blazars of unknown type (BCU) we developed a machine learning method that uses an artificial neural network (ANN) trained with multi-wavelength data. To mitigate the issue of the incomplete spectra, which reduce the ANN’s classification power, we developed a method to fit the spectra of the sources and use the reconstructed spectra in the ANN. We used this method to classify BCUs as BLL or FSRQ. Then we implemented another ANN to find a possible multi-wavelength counterpart for every Fermi-LAT unidentified $\gamma$-ray sources and to classify them as possible Blazar or Not-Blazar sources.

Speaker: Francesco Casini (INFN, Università degli Studi di Perugia)

FC_Poster.pdf

15 Looking for extreme blazars with KM3NeT/ARCA stacking analysis on behalf of the KM3NeT Collaboration

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 neutrinos in the energy range where neutrino detectors are sensitive. A study of these interesting sources is carried out through a likelihood stacking analysis with the KM3NeT/ARCA neutrino telescope. The KM3NeT/ARCA neutrino telescope is a cubic kilometer volume Cherenkov detector, currently under construction, optimised for the observation of TeV-PeV astrophysical neutrinos. Once completed, the detector will consist of 230 Detection Units, each holding 18 digital Optical Modules.
In this contribution, a stacking likelihood analysis of selected extreme blazars from the 3HSP catalog is obtained for the KM3NeT/ARCA detector. The neutrino fluxes of some selected extreme blazars are computed using the AM3 open source modeling code and then compared with km3net ARCA expectation.

Speaker: Maria Rosaria Musone (INFN- sezione NAPOLI, Università degli studi della Campania "L. Vanvitelli")

poster_MRM_worshop2025 (3).pdf

16 Stacking search for KM3NeT/ARCA neutrinos using theoretical blazar models

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 Mediterranean Sea. When completed, KM3NeT/ARCA will encompass a volume of one cubic kilometer and detect neutrinos across a wide energy range, from 100 GeV to multi-PeV. Its modular design allows partial detector operation even during construction. This study introduces a novel framework that integrates theoretical blazar models—developed using the LeHa-Paris code—into binned likelihood stacking analyses based on KM3NeT/ARCA’s data. These models simulate proton-photon interactions and associated radiative processes, employing sophisticated numerical methods to predict neutrino spectra accurately. In parallel, advanced statistical likelihood techniques are being developed to distinguish neutrino signals from background noise. By combining theoretical blazar models with statistical analyses, this methodology aims to enhance the sensitivity of neutrino searches across different blazar subclasses with a particular focus on High-frequency-peaked BL Lacs (HBLs), known for their distinctive emission properties. This approach provides a critical step toward unveiling the connection between photon and neutrino emissions from astrophysical sources, providing insights into the fundamental processes driving high-energy phenomena in the universe.

Speaker: Francesco Carenini (University of Bologna and INFN-BO)

Poster_Carenini_WorkshopMMModeling_ARCA.pdf

17 The Impact of Neutrino Astronomy on Understanding Cosmic Rays

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 acceleration and propagation.
We will review the relationship between cosmic rays and neutrinos, including theoretical models that predict neutrino fluxes resulting from cosmic ray interactions in various astrophysical environments. Recent data from neutrino observatories will be discussed, along with analyses showing how these observations contribute to our understanding of cosmic ray sources and acceleration mechanisms. Additionally, the presentation will explore the potential for future research to address outstanding questions in cosmic ray physics.
By examining the interplay between neutrinos and cosmic rays, we aim to enhance our knowledge of high-energy astrophysical processes and improve our understanding of the most energetic particles in the universe.

Speaker: Dr Ilham El Atmani (Hassan II University of Casablanca, Faculty of Science Ain Chock, High Energy Physics & Condensed Matter Laboratory (PHEMAC))

Poster_Ilham_El_Atmani_DESY_Workshop.pdf

Thursday 27 February

Session 1

18 Facilitating multi-messenger modelling using Gammapy

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, broadband multiwavelength data from optical to gamma-rays are imported into the Gammapy framework. This enables that minimizations are performed directly on instrumental counts instead of flux points, reducing biases coming from the flux points generation, and allowing a simpler treatment of systematics between different instruments and datasets. Additionally, neutrino data can be added once the corresponding instrument responses are provided in a compatible format. These datasets can then be fit to any iterable theoretical model using minimization algorithms via Gammapy. The implementation will be agnostic enough to allow using most leptonic and hadronic models of the community.
In this contribution, we want to present our preliminary implementation focusing on blazars as one of the prime multi-messenger candidates. Additionally, we want to discuss different concrete design and realization possibilities with the community to best address their needs.

Speaker: Lea HECKMANN (APC, CNRS Université Paris Cité)

WorkshopBerlin_2025.pdf

19 A numerical model of blazar jet emission from gradual magnetic dissipation

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 energy dissipation throughout the jet, gradually varying the jet plasma magnetization and its bulk Lorentz factor with distance from the central engine. We adapted it to a leptonic code that self-consistently calculates photon emission within spherical blobs (LeHaMoC). This was done by treating the jet as a series of spheres which interact with each other through radiative transfer. The effects of that radiation spillage are calculated iteratively throughout the jet, accounting for relativistic effects arising from the relative motion of jet segments, until a steady state is reached. We find that this approach produces some distinct differences in the total spectral energy distribution when compared to simply calculating the emission from each constituent sphere of the jet on its own and then adding them up, and can thus be useful in further modeling of expansive emission regions.

Speaker: Stavros Dimitrakoudis (National and Kapodistrian University of Athens)

Dimitrakoudis 2025 DESY A numerical model of blazar jet emission from gradual magnetic dissipation.pdf

20 Advanced Modeling of Blazar Multimessenger Emission Using Neural Networks

I will present a pioneering effort in employing a Convolutional Neural Network (CNN) for the efficient modeling of blazar emissions. Blazars are among the most powerful extragalactic sources, emitting across the entire electromagnetic spectrum, from radio to very high-energy gamma-ray bands. As significant sources of non-thermal radiation, blazars are frequently monitored by various telescopes, leading to the accumulation of substantial multi-wavelength data over different time periods. Also, over the years, the complexity of models of blazar emission has dramatically increased which hinders parameter exploration and makes data interpretation through model fitting challenging. By training the CNN on lepton-hadronic emission models generated for a set of models computed with the kinetic code SOPRANO, which considers the interaction of initial and all secondary particles, the resultant CNN can accurately model the radiative signatures of electron/proton interactions in relativistic jets. This CNN-based approach significantly reduces computational time, thereby enabling fitting to multi-wavelength (photons) and multi-messenger (neutrinos) datasets. The adoption of this AI-driven methodology enables self-consistent modeling of blazar emissions, offering profound insights into their underlying physics and potentially uncovering new astrophysical phenomena.

Speaker: Narek Sahakyan

10:45 Coffee break - Group picture

Session 1

21 Ultra-high-energy cosmic rays from ultra-fast outflows of active galactic nuclei

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 and apply our method to 87 observed UFOs. Nuclei can be accelerated up to $100\,$EeV at the wind-termination shock in some UFOs, but their escaping flux is strongly attenuated due to photonuclear interactions with intense AGN photon fields. In the most extreme $\sim10\%$ of UFOs in our sample, nuclei can escape with energy exceeding $\sim500\,$PeV. In contrast, protons typically escape UFOs with only mild attenuation, with half of the observed UFOs reaching ultra-high energies. We show that UFOs can explain the observed UHECR flux in the transition region below the ankle and potentially contribute to the flux of cosmic-ray nuclei up to the highest energies. An important multimessenger signature is provided by the PeV astrophysical neutrinos expected from interactions of the accelerated cosmic rays in the UFOs.

Speaker: Domenik Ehlert (Norwegian University of Science and Technology)

ufo_presentation_DESY2025_ehlert.pdf

22 MessMapp overview

Speaker: Sara Buson (Z_GA (Gammaastronomie))

23 The KM3NeT ultra-high-energy neutrino and its possible blazar origin

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 promising sources of both astrophysical neutrinos and ultra-high-energy cosmic rays. In this talk, I will present the ultra-high-energy event KM3-230213A and its observed signature. I will describe the identification of seventeen candidate blazars in the 3° radius error region of the neutrino, through their multiwavelength features. The candidates’ properties are characterised throughout the whole electromagnetic spectrum, from radio to gamma rays, thanks to a wide collection of archival data and dedicated observations. Three sources exhibit flaring behaviour in one of the examined bands, in coincidence with the neutrino arrival time. While none of these can be unequivocally associated with the neutrino, I will discuss the implications of a possible blazar origin for the KM3NeT event.

Speaker: Massimiliano Lincetto (Z_GA (Gammaastronomie))

LINCETTO KM3NeT UHE Numerical MM WS-1.pdf

12:45 Lunch

Session 2

24 Multi-gamma-ray-state SED analysis of highly variable blazars

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 Lac objects: Mrk 421, S5 0716+71, PKS 2155-304, and OJ 287. We performed a multi-state SED analysis, systematically examining the sources across
diverse flux states: quiescent, flaring, and intermediate states. The SED analysis reveals interesting and complex behaviors across the observed.
sources.A detailed investigation of PKS 2155-304 highlighted its complex
behavior, while the analysis of OJ 287 provided particularly compelling
evidence of a notable shift in X-ray emission from the inverse Compton to the synchrotron peak region, constraining the physical processes at the emission sites. Through modeling, we obtained crucial parameters characterizing the jet environment. These parameters provide insights into the physical conditions,such as particle acceleration and energy transfer processes, within the relativistic jets.

Speaker: Gopal Bhatta (University of Zielona Gora)

DESY25_Bhatta.pdf

25 Fermi-LAT Detection of the Low-luminosity Radio Galaxy NGC 4278 during the LHAASO Campaign

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 J1219+2915 at the time of the LHAASO detection. Our analysis revealed evidence for a new point-like source, detected at a statistical significance of TS~29, spatially consistent with the LHAASO detection and the radio position of NGC 4278. We observed a hard spectrum in the Fermi-LAT band, with two very high-energy (VHE) photons (~100 GeV) associated with NGC 4278 with a probability exceeding 99%.
Our results provide further support to the association between the LHAASO source and the NGC 4278, posing new challenges for our understanding of the physical processes acting in relativistic jets.

This finding demonstrates that not only blazars or bright extended radio galaxies but also compact, low-luminosity radio galaxies can surpass the sensitivity thresholds of GeV and TeV instruments, paving the way for future studies with the Cherenkov Telescope Array Observatory.

Speaker: Ettore Bronzini (University of Bologna & INAF-OAS)

26 Analytic nuclear cascades: a unified framework for UHECR sources and propagation

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 the probabilistic quantities but may be limited by computation time, while ODEs can be faster at the cost of neglecting the stochastic effects. The limitations of each of these approaches are known and somehow complementary, yet, a framework where the speed of computation is not sacrificed while including the stochastic effects would have much scientific potential by overcoming the current limitations.
This is the goal of the probabilistic description presented in this work, which is based on the theory of matrix exponential distributions. This approach provides analytical expressions for the probability distributions of the nuclear cascades resulting from interactions of UHECR nuclei in both sources and during propagation. The description allows for a larger number of nuclear species due to being easily computable, and integrates nuclear decays without the need of ad-hoc limitations on nuclear species on the basis of the decay time. The inclusion of more complex effects such as time variable photon fields, magnetic diffusion and escape in this framework are also discussed, emphasizing that no additional simplifying assumptions are required to achieve a time efficient and precise computation. The method is implemented in a python package called CRISP, to be presented in this talk.

Speaker: Leonel Morejon (Wuppertal University)

LMorejon_WNM3_26.02.25.pdf

27 GAMERA - A tool for multi-messenger modelling in high-energy astrophyiscs

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 wrapper facilitates the easy use in Python. In this contribution, I will
give an overview of the package, outlining its general structure, functionalities
and applications.

Speaker: Mischa Breuhaus (Centre de Physique des Particules de Marseille (CPPM))

GAMERA_Mischa_Breuhaus.pdf

28 DIPLODOCUS: an anisotropic Boltzmann equation solver designed to model AGN jet dynamics and emissions

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 space, allowing self-consistent particle transport along the jet axis. The code has two parts: to evaluate anisotropic particle interactions, a new framework has been developed to pre-compute collision integrals via Monte-Carlo sampling; and a conservative solver for general Boltzmann equations, which may include non-conservative forces such as radiation reaction. Both operate under a formalism denoted "distribution-in-plateaux", whereby the underlying particle distribution functions are discretised by use of Heaviside step functions, rather than Dirac delta functions which are used in particle-in-cell. As such, they uniformly sample momentum space, allowing constant accuracy over all energy ranges.

Speaker: Christopher Everett (University of Oxford)

Presentation1.pptx

15:45 Coffee break

Session 2

29 Accounting for mixing in synchrotron spectral modelling of flickering AGN jets using Lagrangian particles

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 this module to account for the mixing of shocked material with unshocked material, which we find is particularly important for systems with high density contrast between these two populations.

This talk will focus on the adaptations made to account for mixing between shocked and unshocked populations and to allow this modelling in RHD simulations and will cover some early results from the work so far.

We plan to use our simulations to assess the applicability of spectral ageing models to radio observations of jets from AGN, particularly in cases where the jet has a power which varies over time. Estimating the ages of AGN is a key component in being able to estimate the duty cycle and jet power of these systems. By estimating the strength of the magnetic field based on the internal energy density of the fluid, rather than by evolving the magnetic field in a relativistic magnetohydrodynamic (RMHD) simulation, we mirror observational approaches based on equipartition arguments and separate the analysis of the effects of varying jet power from those of detailed shock acceleration physics.

Our approach will allow us to quantify the effects of mixing and of electrons passing through multiple shocks on the energy spectra of the electron populations. Early results suggest that in highly variable jets, the source might look younger after high power periods than after lower power periods due to increased injection of energy into newly shocked material and that we might expect more distinct patches of recently shocked material further back in the lobes shortly after a period of high jet power.

References:

Mignone, A. et al. 2007, PLUTO: A Numerical Code for Computational Astrophysics. The Astrophysical Journal Supplement Series, 170

Mukherjee, D. et al. 2021, Simulating the dynamics and synchrotron emission from relativistic jets – II. Evolution of non-thermal electrons. MNRAS, 505

Vaidya, B. et al. 2018, A Particle Module for the PLUTO Code. II. Hybrid Framework for Modelling Nonthermal Emission from Relativistic Magnetized Flows. The Astrophysical Journal, 865

Speaker: Emma Elley (University of Oxford)

DESY_MM_Numerical_Modelling_EE.pdf

30 Axion Gamma-Ray Signatures from Quark Matter in Neutron Stars and Gravitational Wave Compar- isons

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 emissivities $\epsilon_a$ can be derived, from which fluxes can be determined. We predict a photon flux which may be detectable by Fermi LAT, and limits on the QCD mass $m_a$. In this model, axions decay to gamma rays in a 2-photon vertex. We may determine the expected fluxes from the theoretical emissivity. The sensitivity curve from the Fermi Large Area Telescope (Fermi LAT) would allow axion mass constraints for neutron stars as low as $m_a \le 10^{-14}$ eV 95$\% C.L.$. Axions could thus be detectable in gamma rays for neutron stars as distant as 100 kpc. A signal from LIGO GWS 170817 could be placed from the NS-NS merger, which gives an upper limit of $m_a \le 10^{-10}$ eV.

Speaker: Bijan Berenji (SLAC National Accelerator Laboratory / California State University, Dominguez Hills (CSUDH))

axion_gamma-ray_gravitational-wave.pdf

31 Black hole-neutron star (NSBH) coalescence events

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 forthcoming upgrades to the LIGO-Virgo-Kagra (LVK) interferometers,
and particularly with the prospective implementation of next-generation instruments such as the Einstein Telescope (ET), we anticipate a substantial increase
in the detection rate of these events, potentially by orders of magnitude.

The study of NSBH coalescences, alongside neutron star binary (BNS) mergers, is pivotal due to their status as prime multimessenger candidates capable of producing
a wide range of electromagnetic counterparts, including Gamma-ray Bursts (GRBs) and Kilonovae. By conducting joint analyses of both the gravitational and electromagnetic signals,
it becomes feasible to derive more precise insights into the properties of the involved celestial objects and the myriad processes occurring during and subsequent to the merger,
including the neutron star's stiffness and the mechanisms underlying GRB generation and beam structure.

This work provides an estimation of the combined detection capability for gravitational signals and GRBs originating from NSBH events,
considering the anticipated upgrades to existing instruments and the deployment of next-generation facilities. In assessing the gravitational wave detectors,
we compare the LVK interferometers with ET employing the GWFish software, while for evaluating the detectability of GRBs, particularly focusing on the afterglow component,
we primarily reference Fermi and the prospective CTA array telescope. By utilizing state-of-the-art models for beam formation and propagation, we investigate how the goodness
of information derived from these events is contingent upon the instruments utilized and the inherent characteristics of the coalescence itself.

Speaker: Tobia Matcovich (Istituto Nazionale di Fisica Nucleare))

Numerical-workshop-DESY.pdf

32 Progress on cuHARM, a code for GR-R-MHD equations on graphics processing units

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 closure relations or on the assumption of grey transport. I will further discuss the implementation on graphics processing units (GPUs) to accelerate the computation, with an emphasis on performance, bottlenecks and scalability. I will conclude the talk by discussing future developments.

Speaker: Damien Begue (Bar-Ilan University)

Begue_cuHARM_2.pdf

19:00 Social dinner

Friday 28 February

Session 1

33 Insights from modelling the brightest Fermi-LAT blazar flare

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 observed emission with the AM$^{3}$ program for the time-dependent simulation of radiative processes. We show that each of the one-day averaged SEDs can be well described with a leptonic model producing the observable emission originating from a $\sim 10^{16}$-cm-sized region located beyond the outer radius of the broad-line region (BLR). We show that the emission region (blob) should be a quasi-stationary feature in the jet into which the relativistic plasma with a high bulk Lorentz factor ($\Gamma\sim20-40$) is injected while an attempt to model the blob as moving along with the bulk motion of the jet plasma results in a poor description of the data. By adding protons into the blob and using the high-statistics X-ray data to constrain the hadronic contribution, we obtain the expected neutrino yield from 3C 454.3 in different states of its activity. Extending the model of 3C 454.3 to the whole population of Fermi-LAT FSRQs we estimate their contribution to the observed IceCube neutrino flux at energies $\geq 100$ TeV.

Speaker: Egor Podlesnyi (Norwegian University of Science and Technology (NTNU))

Podlesnyi 3rd Workshop on Numerical Multi-Messenger Modelling.pdf

34 Delayed Radio Flares in Blazars Associated with High Energy Neutrinos from Expanding Leptohadronic Plasma Blobs

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, simultaneously with a flux enhancement in the gamma-rays, indicating the presence of a hadronic population in the jet. Intriguingly, no radio flare accompanied the neutrino event. However, two years later, the radio flux increased significantly, suggesting that the jet was initially radio-opaque and that the radio and high-energy emission regions lie at different scales along the outflow. This pattern of delayed radio flares relative to high-energy outbursts also appears in other blazars associated with high-energy neutrino emission. Motivated by these observations, we investigate whether an expanding emitting region, containing a leptohadronic particle population and propagating along the jet, can reproduce the spectral features for the case of TXS 0506+056 and the observed time lag between radio and high-energy signals.

Speaker: Stamatios Ilias Stathopoulos (National and Kapodistrian University of Athens)

WNMMM DESY 25.pptx

35 Impact of model parameter degeneracy on leptonic radiation models

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 models have been proposed to explain the production of blazar radiation. The one-zone leptonic model describes the low-energy emission as synchrotron photons emitted by electrons, which are then upscattered to higher energies by the same electrons. However, one-zone leptonic models have a high number of free parameters leading to possible degeneracy of the modeling results. This work aims to determine the extent to which we can constrain the parameters based on the available data. We apply and compare five different methods of searching for the best-fit parameters. Using the visualization tool t-SNE, the high-dimensional parameter space is visualized with the aim to show parameter sets of the leptonic model with higher similarities closer to each other. The parameter space is analyzed with simulated and observational data of blazar PKS 0735+178 and Markarian 501. We present the maps of the parameter space and discuss the physical implications of the obtained results.

Speaker: Frederike Apel (None)

Apel_parameter_degeneracy.pdf

10:45 Coffee break

Session 1

36 Neutrino Emission from Bright Blazar Flares

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 used in Kreter et al. (2020) may overstate the increase in neutrino production when applied to proton-synchrotron blazar models but do correctly predict the general trend. Additionally, we show that while the lack of detection of these neutrinos with current observatories is not inconsistent with their presence, future detectors may indeed be able to confirm their existence or the lack thereof.

Speaker: Joshua Robinson (North-West University)

Neutrino_Emission_from_Bright_Blazar_Flares_Robinson.pdf

37 Radiative models for rapid blazar flares

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 of the physical origin of blazar flares is still missing.
In our team, we have carried out a systematic study of the expected shapes of multi-wavelength flares for a range of particle acceleration and re-acceleration scenarios to establish characteristic observable signatures, such as time delays between energy bands, asymmetries and plateaux.
We have also investigated a particular scenario where rapid variability is due to the expected variation in the external radiation field for an accelerated plasma blob, without variations in the particle injection or acceleration.
Both studies are using a time-dependent leptonic code based on a Fokker-Planck equation of the particle evolution.

Speaker: Andreas Zech (LUX, Observatoire de Paris, CNRS, PSL University, France)

Zech_modelling_Zeuthen_2025.pdf

38 Closing session

Speaker: Sara Buson (Z_GA (Gammaastronomie))