The nature and origin of magnetic fields on cosmological scales are still unclear. Magnetic fields detected in galaxies and galaxy clusters are typically interpreted as the result of the amplification of weak seed fields, but their nature remains largely unknown with two scenarios considered: the cosmological and the astrophysical origin. Signatures of magnetization in cosmic voids from observations of very high energy (VHE, E > 100 GeV) photons from extragalactic sources can provide crucial results. Indeed, if a non-negligible intergalactic magnetic field (IGMF) is present in the voids, a time-delayed emission known as pair-echo is expected. The timing and intensity of this signal encode information on the IGMF strength B and properties. Given the recent detection of GRB afterglows at TeV energies, in this article we perform a detectability study of pair-echo signatures from GRBs. We simulate afterglow emission for different values of the jet kinetic energy (E_k,iso = 10^49 - 10^55 erg), redshift (z = 0.03 - 1), and lightcurve break times, and estimate the expected pair-echo radiation for IGMF strengths in the range B = 10^-19 - 10^-16 G. We investigate the capability of CTAO to detect the resulting emission at tens of GeV. We find that a subsample of GRBs in the z - E_k,iso parameter space can produce a detectable pair-echo component for CTAO for all the tested IGMF strengths. A steepening of the GRB afterglow light curve, caused e.g. by an early (0.1 - 1 days) jet break, is a key factor to increase the chances of detection. CTAO observations starting from 10 - 12 hrs up to a few days after the GRB trigger time can provide relevant results to probe IGMF.

A significant fraction of the energy from the gamma-ray burst (GRB) jets, after powering the keV–MeV emission, forms an ultra-relativistic shock propagating into the circum-burst medium. The particles in the medium accelerate through the shock and produce the afterglow emission. Recently, a number of GRB afterglows were observed in TeV γ-rays by Cherenkov Telescopes. This new observational window provides access to the broad-band spectra of GRB afterglows, which contain rich information on the microphysics of relativistic shocks and the profile of the circum-burst medium. Since the transition from synchrotron to inverse Compton regime in afterglow spectra occurs between hard X-rays and the very-high-energy (VHE) γ-rays, it is necessary to have a detection in one of these bands to identify the two spectral components. The early afterglow data in hard X-rays, along with the GeV emission, could help to accurately constrain the spectral shape and capture the spectral turnover to distinguish the two components. We present a multi-wavelength spectral and temporal study, focussed on the keV-VHE domain, of GRB 230812B, one of the brightest GRBs detected by Fermi Gamma-ray Burst Monitor (Fermi/GBM). We also include the detection of a 72 GeV photon by Large Area Telescope (Fermi/LAT) during the early afterglow phase. Through detailed modelling of the emission within the afterglow external forward shock in a wind-like scenario, we predict the multi-wavelength afterglow observations from optical (up to approximately one day) to high-energy band. We emphasise the importance of following up poorly localised GRBs by demonstrating that even in cases without prompt localisation, such as GRB 230812B, it is possible to recover the emission using imaging atmospheric Cherenkov telescopes (IACTs) thanks to their relatively wide field of view. The low energy threshold of the Large-Sized Telescope is essential in discovering the VHE component at the much higher redshifts typical for long GRBs.

On date 9th of October 2022, an exceptionally bright Gamma-Ray Burst, GRB 221009A, was detected by several observatories, both ground- and space-based. It has been the highest flux Gamma-Ray Burst ever observed, with an energy Eiso ∼ 1055erg, and its detection was followed by many studies. In our work, we model the very high energy (E> 100 GeV) afterglow light curve published by the LHAASO Collaboration using a numerical modelling and an analytical approach to constrain the Gamma-Ray Burst free parameter space. The light curve in the (0.3 - 5) TeV range, as detected by LHAASO, shows a simple broken power law shape, with the peak around ∼11 s after the trigger. We estimated the afterglow parameters using a Maximum Likelihood Estimation followed by a Markov-Chain Monte Carlo. In this way, we obtain the fiducial confidence intervals. We found some interesting preliminary results about the parameter distributions, in reasonable agreement with other studies.

A significant fraction of the energy from the γ-ray burst (GRB) jets, after powering the keV-MeV emission, forms an ultra-relativistic shock propagating into the circumburst medium. The particles in the medium accelerate through the shock and produce afterglow emission. Recently, a few GRB afterglows have been observed in TeV γ-rays by Cherenkov Telescopes. This provides access to broadband spectra of GRB afterglows containing rich information about the microphysics of relativistic shocks and the profile of the circumburst medium. Since the transition from synchrotron to inverse Compton regime in afterglow spectra occurs between hard X-rays and the very-high-energy (VHE) γ-rays, detection in one of these bands is required to identify the two spectral components. The early afterglow data in the hard X-rays, along with the GeV emission, could accurately constrain the spectral shape and help in capturing the spectral turnover to distinguish the two components. We present the multiwavelength spectral and temporal study, focused on the keV-VHE domain, of GRB 230812B, one of the brightest GRBs detected by Fermi Gamma Ray Burst Monitor (GBM), along with the detection of a 72 GeV photon in Large Area Telescope (LAT) during the early afterglow phase. Through a detailed modelling of the emission within the afterglow external forward shock in a wind-like scenario, we predict optical to high-energy observations up to 1 day. We emphasize the importance of following up poorly localised GRBs by demonstrating that even without prompt sub-degree localisation, such as in GRB 230812B, it is possible to recover the emission using imaging atmospheric Cherenkov telescopes, thanks to their relatively wider field of view. Moreover, we show that the low energy threshold of Large-Sized Telescope is essential in discovering the VHE component at much higher redshifts, typical of long GRBs.

Gamma-ray bursts (GRBs) are one of the main targets for the observations of the MAGIC telescopes. As a result of the effort in improving the sensitivity of the instrument and the automatic follow-up strategy, MAGIC detected two GRBs in the very-high-energy (VHE, E>100 GeV) range, namely GRB 190114C and GRB 201216C. In GRB 190114C (z=0.42), the data collected by MAGIC revealed a new emission component at sub-TeV energies in the afterglow of the GRB. The very rich multi-wavelength dataset, spanning 17 orders of magnitude in energy, allowed to perform a detailed modelling of the broadband emission. The multi-wavelength data could be modelled within a one-zone synchrotron-self Compton scenario with internal γ-γ absorption, where the model parameters are compatible with those found in previous GRB afterglow studies below GeV energies. Similarly, GRB 201216C broadband emission could be explained using the same model, although the amount of simultaneous multi-wavelength data is reduced with respect to GRB 190114C. In particular, GRB 201216C challenged the current MAGIC detection potential, as its redshift was determined to be z=1.1, strongly reducing the observed gamma-ray flux but making it the most distant source detected at VHE. These two detections, accompanied by evidence of VHE emission from a few more GRBs, opened up new questions such as the presence of sub-TeV emission in different classes and phases of GRBs. In this contribution we will present the status of the MAGIC GRB follow-up program, with an highlight on its detected GRBs. Moreover we will show the results on the GRBs observed by MAGIC from 2013 to 2019 with no evidence of VHE emission, in particular for those with simultaneous X-ray observations and redshift z<2. We will discuss the implications of these results for GRB physics and the challenges and prospects for future GRB observations with MAGIC.

We present the results of a multi-wavelength study of blazars selected from the 5th ROMABZCAT catalog. We selected from this sample a subsample of 2435 objects having at least one counterpart in one of the three main archival X-ray catalogs, which is, the fourth release of the XMM-Newton Survey Science Catalogue, the second release of the Chandra Source Catalog, and the second Swift X-ray Point Source catalog of detections by Swift-XRT, or in the recently released eROSITA-DE Data Release 1 catalog. We first searched for different multi-wavelength trends between sources with a Gamma-ray counterpart in the Fermi-LAT 14-year Source Catalog (4FGL-DR4) and sources lacking one. We find that the non-4FGL sources are on average fainter both in the X-rays and in the radio with respect to the 4FGL-detected ones, but the two samples have similar X-ray-to-radio flux ratios, as well as synchrotron peak frequencies. We then focused on the 1007 non-Gamma-ray detected population, to determine if there is a sample of X-ray sources that could be TeV emitters. We find that a large number of sources, mostly BL Lacs or BL Lacs with host-galaxy contribution to the spectral energy distribution, have large synchrotron peak frequency and X-ray to radio flux ratio, two properties that characterize the vast majority of known TeV emitters. With respect to these known TeV emitters, our targets have X-ray fluxes 1 order of magnitude fainter. We then computed the 0.2-12 keV and 20 GeV - 300 TeV fluxes for the known 5BZCAT TeV emitters, and determined the existence of a direct correlation between X-ray and TeV fluxes in the BL Lacs population. We used this trend to estimate the VHE flux of our targets, and found a promising sample of sources for follow-up observations with current or future, more sensitive, Cherenkov telescopes, first and foremost the Cherenkov Telescope Array Observatory.

Cosmic rays are energetic, subatomic particles constantly reaching the Earth atmosphere from all directions. Several technological tools currently available can be used to introduce the students to research activities in the particle physics field. The Legnaro National Laboratories (LNL) of the Italian Istituto Nazionale di Fisica Nucleare (INFN) host a muon telescope. This telescope is formed by plastic scintillators and silicon photomultipliers, mostly used for outreach purposes during the International Cosmic Day (ICD). It is well known that local atmospheric parameters affect the rate of muons reaching the Earth's surface. In this contribution, we, along with high school and bachelor students in Physics at the University of Padova, investigate the anticorrelation between muon counts and atmospheric pressure. This correlation was measured with the muon telescope in LNL using the data collected in 2022 and 2023. The results from our analysis confirm the presence of a significant anticorrelation. Further analyses with a larger datasample allow us to improve the precision of the result, as well as possibly investigate other atmospheric-related correlations, such as with temperature and humidity and the variation in time of these correlations. In addition, we bought a new educational tool: a Cosmic Hunter detector developed by the CAEN group. We are currently testing the instrument performances and we plan to use this instrument to confirm our results and explore new possible educational activities for students.

On October 9th, 2022, the brightest gamma-ray burst (GRB) since the first GRB observation in the late sixties was detected by the Fermi-GBM and Swift-BAT telescopes (GRB 221009A). The outstanding characteristics of this GRB triggered extensive follow-up observations of the source across all wavebands, including at very-high-energy (VHE) gamma rays with the Large-Sized Telescope prototype (LST-1) of the upcoming Cherenkov Telescope Array Observatory (CTAO). In this contribution, we present the analysis and results of the LST-1 observation campaign in October 2022, focusing on the data taken under nominal observing conditions and above 200 GeV.

The detection of gravitational waves from a binary neutron star merger by Advanced LIGO and Advanced Virgo (GW170817), along with the discovery of the electromagnetic counterparts of this gravitational wave event, ushered in a new era of multimessenger astronomy, providing the first direct evidence that BNS mergers are progenitors of short gamma-ray bursts (GRBs). Such events may also produce very-high-energy (VHE, > 100GeV) photons which have yet to be detected in coincidence with a gravitational wave signal. The Cherenkov Telescope Array (CTA) is a next-generation VHE observatory which aims to be indispensable in this search, with an unparalleled sensitivity and ability to slew anywhere on the sky within a few tens of seconds. New observing modes and follow-up strategies are being developed for CTA to rapidly cover localization areas of gravitational wave events that are typically larger than the CTA field of view. This work will evaluate and provide estimations on the expected number of of gravitational wave events that will be observable with CTA, considering both on- and off-axis emission. In addition, we will present and discuss the prospects of potential follow-up strategies with CTA.

In recent years, the MAGIC telescopes have been equipped with a setup that allows its Imaging Atmospheric Cherenkov Telescopes (IACTs) to function as an Intensity Interferometer. The deadtime-free setup includes a 4-channel GPU-based real-time correlator together with optical filters in the 350-450 nm wavelength range and specialized Active Mirror Control (AMC) configurations. This implementation allows MAGIC to perform measurements of the spatial coherence (visibility) of the intensity fluctuations of an object’s starlight over several separations (baselines) and construct a model of said object. The accessible baseline range for MAGIC is ~40-90 m which translates into an angular resolution of 0.5-1 mas. Additionally, thanks to the AMC it can access even smaller baselines, of less than 17 m (which is the diameter of each of both dishes) to measure objects of greater angular size (>1 mas) and even measure the zero-baseline correlation, which is key to calibrate the system. We present the latest measurements that allow us to understand the performance and systematics of our setup and validate our analysis.

Recently, several gamma-ray bursts (GRBs) have been detected in the very-high-energy (VHE) gamma-ray energy range by ground-based gamma-ray experiments such as MAGIC, H.E.S.S., and LHASSO. For some GRBs, the VHE emission is consistent with synchrotron self-Compton (SSC) emission from high-energy electrons accelerated in the forward shock of the relativistic jet. However, more statistics are needed to further constrain the emission models. GRB 201216C is a long bright GRB detected in a broad energy range from radio to VHE. The redshift is estimated to be 1.1, making the GRB the most distant source detected in the VHE energy range. MAGIC started the observation 56 seconds after the GRB was triggered by the Swift-BAT telescope. We performed a detailed analysis and detected the signal with about 6 sigma in the first 20 minutes. MAGIC continued the observation for 2.2 hours on the same night and 4 hours on the next night. No signal was detected later than 40 minutes after the GRB trigger. We have performed modelling of the multi-wavelength emission using the MAGIC data. We analysed simultaneous optical data from Liverpool Telescope with MAGIC and included the results in the modelling. The sub-TeV emission is consistent with the single-zone SSC model in the forward shock. In this presentation, we show the final results of the MAGIC data analysis of GRB 201216C and discuss the emission mechanism of the multi-wavelength data.

The instrumentation for gamma-ray astronomy has advanced tremendously during the last two decades. The study of the most violent environments in the Universe has opened a new window to understand the frontier of physics, exploring processes that are beyond the capabilities of Earth- based laboratories to replicate. One of the instruments at the forefront of gamma-ray astronomy is the MAGIC stereoscopic system, which consists of two 17-m diameter mirror dish telescopes located at 2200m a.s.l. on the Canary Island of La Palma, in Spain. The year 2023 marks the 20th anniversary of MAGIC, reaching the milestone of 200 publications in peer-reviewed journals over a wide range of research areas, covering astrophysics with Galactic and extragalactic objects, dark matter searches, and cosmology. MAGIC has established itself as a world-wide leading instrument for gamma-ray astronomy in the energy range from 20 GeV to beyond 100 TeV. MAGIC is an active participant in multiple multiwavelength and multimessenger observational campaigns, contributing to our understanding of the universe. In the conference, I will provide a status report of MAGIC, including the discussion of a few outstanding results during the last two decades and the prospects for the near future.

The recent discovery of PeV gamma-ray emission especially from the LHAASO observatory, located in the Northern hemisphere, boosted the relevance of observing the Southern sky at such energies. SWGO (SouthernWide-Field Gamma-Ray Observatory) is the largest proposed detector with sensitivity in the 100 TeV-1 PeV energy range. The baseline SWGO idea is a km^2 array of water tanks to be placed above 4,400ma.s.l. in the Andes, South America. In this contribution, we have studied the particle content and the morphology of Extensive Air Showers (EAS) generated by photons and protons in the 0.1 to 10 PeV energy range. We have simulated over 106 gamma-rays and proton induced showers respectively with primary energy in the 0.1-10 PeV energy range. We also show the particle distribution at ground, the lateral profile, the muon content and the average particle properties at ground.

A decade has passed since high-energy astrophysical neutrinos have been discovered by IceCube, however the corresponding sources have not been fully identified yet. The reported coincidence of the high-energy IceCube-170922A with the gamma-ray blazar TXS 0506+056 is not enough to claim that blazars are the dominant high-energy neutrino emitters in the Universe. In fact, recently IceCube announced a second correlation with NGC 1068, a nearby Seyfert galaxy, which is significantly different from a gamma-emitting blazars. The hunt for counterparts of the IceCube neutrinos using gamma-ray telescopes started in 2012. Nonetheless, these efforts will continue with the next-generation gamma-ray telescopes, such as the CTA Large Size Telescopes (LSTs) and other telescopes, by means of an improved and revised observation strategy. These new observations will allow us to detect enough sources in order to elucidate the mystery of the neutrino emitters. In this contribution, we introduces the efforts made thus far in the search for gamma-ray counterpart of high-energy IceCube events using the current generation IACTs, focusing on alerts made of multiple neutrinos events, and present an idea to improve in the observational strategies with the CTA LSTs that will become operational in the coming decade. We will discuss how to reduce the bias to gamma-ray emitters in order to search for possible neutrino counterparts.

Despite the advancement in background rejection techniques, observation of the very-high-energy gamma-ray sky by imaging atmospheric Cherenkov telescopes (IACTs) are subject to an irreducible background from gamma-like hadron- or electron-induced air showers. The determination of this residual background is crucial for accurate spectral and spatial measurements. The Cherenkov Telescope Array (CTA) will become the next generation of IACTs. To unveil its full potential, the improved reconstruction performance of CTA needs to be coupled with a reliable background estimate across the entire field of view. This may become especially important in the case of the planned surveys of large areas of the sky. In this contribution we will present pybkgmodel, an open-source python software package developed for CTA. It aims at providing in a consistent way the various background modelling methods, based on the experience from current IACTs such as H.E.S.S, MAGIC, and VERITAS. It is designed as a toolbox allowing a user to easily choose the optimal reconstruction approach for various target regions or a combination of several algorithms. We will introduce the design of the package as well as demonstrate its performance using simulations for the CTA Large-Sized Telescope prototype (LST-1).

In 2020, the MAGIC collaboration started an initiative to improve diversity, equity and inclusion (DEI) in the collaboration. One of the major actions undertaken by this initiative was a survey which was distributed among all MAGIC members with the goal of getting a clear picture of the status quo and to identify potential problems or opportunities concerning DEI related topics. Two surveys have since been performed - one in December 2020 and one in June 2022 - covering questions related to demographics, working conditions, recognition, harassment, bullying and discrimination. In this contribution, we present the questionnaire and strategy used to run these surveys. Additionally, we describe the impact the survey had within the collaboration and which actions have been taken as a direct consequence of the survey results.

The prototype Large-Sized Telescope (LST-1) of the Cherenkov Telescope Array Observatory (CTAO) is in commissioning phase at the Observatorio del Roque de Los Muchachos at 2200 m a.s.l. in La Palma (Canary Islands, Spain). LST-1 is a 23-m diameter telescope and is the first of four that will compose the LST part of the CTAO Northern array. The LST subarray is optimized to provide the best sensitivity for gamma rays in the 20 GeV - 200 GeV energy range. The MAGIC telescopes, which are located approximately 100 m from the LST-1, is operating as a two 17-m telescope stereoscopic system for more than 14 years. LST-1 and MAGIC routinely perform joint observations of gamma-ray sources to exploit the potential of the three-telescope system. This contribution describes the analysis pipeline and evaluates the performance of the system using Monte Carlo simulations and data on the Crab Nebula. The sensitivity achieved during joint observations with MAGIC and LST-1 is about 30% higher than that of MAGIC alone.

The prototype Large-Sized Telescope (LST-1) of the Cherenkov Telescope Array (CTA) was inaugurated on La Palma, Canary Islands, in 2018. Since then, the telescope is in the commissioning phase and takes regular gamma-ray data on astrophysical sources while waiting for other CTA telescopes in La Palma to be constructed. Here we present the status of the commissioning, lessons learned, the telescope performance, and scientific highlights achieved in the last couple of years. The science results include the detection of active galactic nuclei flares, studies of pulsar wind nebulae and pulsars, the detection of a Nova, and searches for gamma-ray emission from gamma-ray bursts. We also present the status of the construction of the three further LST telescopes (LST-2-4) in La Palma and plans for their commissioning.

Clusters of galaxies are the largest gravitationally-bound structures in the Universe. They are composed of galaxies and gas (approximately 15% of the total mass) mostly dark matter (DM, accounts up to 85% of the total mass). If the DM is composed of Weakly Interacting Massive Particles (WIMPs), galaxy clusters represent one of the best targets to search for gamma-ray signals induced by the decay of WIMPs, with masses around the TeV scale. Due to its sensitivity and energy range of operation (from 20 GeV to 300 TeV), the Cherenkov Telescope Array (CTA) Observatory has a unique opportunity to test WIMPs with masses close to the unitarity limit. This will complement the searches for DM from other gamma-ray observatories as well as direct and collider experiments. The CTA Observatory is planning to search for gamma-ray emission, either its origin may be cosmic-ray (CR) or DM related, in the Perseus galaxy cluster during the first years of operation. In this poster, we will present the software created to perform the analysis using the \texttt{ctools} software and the corresponding results.

Water-Cherenkov detectors (WCD) have been manufactured in Australia by the company AQUA-MATE as part of the RD activities for SWGO. They consist of a steel tank frame with a bladder on its interior satisfying the SWGO double-layer tank design. Tanks and bladders have been custom designed to optimally accommodate the bladder inside the tank and with minimal material usage. They are delivered in compact boxes that are easy to transport. These boxes are designed to fit 24 tanks in a 20-foot container. The double-layer tank design has introduced new features to improve the discrimination between gamma-rays and cosmic rays. Some of these features created challenges for the manufacturing. Some units have been delivered to one of Peru’s candidate sites at 4800 m and to Mexico (the HAWC Observatory, 4100 m) for prototype tests in real conditions. In this contribution we will describe manufacturing and construction details of the first SWGO prototype WCD. These details were envisaged to facilitate: the transport of the units, the assembly, the deployment and maintenance activities of the detectors. Furthermore, the units need to be resistant to strong winds, rain, snow and earthquakes.The costs are scalable with the detector volume. This information could be of interest to other Observatories that are in RD phase, such as the Global Cosmic Ray Observatory (GCOS) for the study of the highest-energy particles in the Universe and the Tau Air Shower Mountain-Based Observatory (TAMBO) for the search of PeV neutrinos.