The main goal of the Pulsar Timing Array is to regularly monitor tens of millisecond pulsars in the radio band to detect dynamic perturbations of the space-time metric, such as those caused by the passage of gravitational waves. So far, pulsar networks are the only way to detect gravitational wave emission in the nanohertz frequency range. The talk will discuss the current status of Pulsar...
Pulsar Timing Array experiments can probe the presence of possible scalar
or pseudoscalar ultralight dark matter particles through decade-long timing of
an ensemble of galactic millisecond radio pulsars. If dark matter interacts only
gravitationally with ordinary baryonic matter, our findings show that ultralight
particles with masses 10$^{−24.0}$ eV $\leq$ m $\leq$ 10$^{−23.3}$ eV can...
The brightest of all time (BOAT) GRB 221009A has been observed across all the electromagnetic spectrum. The observations of the BOAT in the MeV gamma-rays have revealed a presence of a new feature in the spectrum of the prompt emission - a narrow and variable MeV line. The early GeV and TeV observations have allowed for the detailed characterisation of the afterglow radiation of the BOAT. In...
By releasing the first image of the black hole shadows of M87 and Sgr A, the EHT Collaboration has achieved one of the most illustrious scientific results of the last few years. Beyond the formidable technical accomplishment, the two images had a fundamental impact on our understanding of the physics of black holes and AGNs, and provided a further striking confirmation of general relativity....
The observation by the LHAASO Collaboration of the gamma-ray burst GRB 221009A at energies up to (13-18) TeV challenges conventional physics. This GRB originated at redshift z = 0.151, whence emitted photons at energies above 10 TeV are hardly observable on Earth due to their interaction with the extragalactic background light (EBL) photons. Indeed, if the most recent and accurate EBL model to...
Cosmic rays prove that our Universe hosts elusive astrophysical ”monsters” capable of continuously and efficiently accelerate particles at extreme energies. High-energy photons and neutrinos may provide the ultimate key to decipher the mystery of cosmic rays. Amongst the most promising neutrino candidate sources of high-energy neutrinos there are blazars, active galactic nuclei hosting a...
Pulsar Timing Array (PTA) experiments use well-timed pulsars to probe the gravitational universe at frequencies down to a few nanohertz. This band is populated by gravitational waves emitted by binary systems of supermassive black holes (SMBHBs). The most common signal sought by PTA experiments is a stochastic gravitational wave background generated by the superposition of hundreds of...
Although the recent evidence presented by Pulsar Timing Arrays (PTAs) is that for a stochastic Gravitational Wave Background (GWB), which was most likely produced by the superimposition of several GW signals, simulations of the merger history of supermassive black hole binaries (SMBHBs) suggest a narrow possibility of the detection of some of the most massive or fortunately located individual...
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...
Axion-like particles (ALPs) are a common feature in several extensions of the Standard Model, arising, for example, as a solution to the strong CP problem in quantum chromodynamics, or as a prediction of string theories. A significant property for the experimental detection of ALPs is their coupling to photons, which enables ALP-photon conversions in ambient magnetic fields.
In particular,...
The simultaneous observation of gamma rays and neutrinos from the same astrophysical source allows us to understand the mechanisms of particle production in the ultra-high energy environments of our Universe.
The Cherenkov Telescope Array Observatory (CTAO) is a new-generation ground-based instrument for very-high-energy gamma-ray astronomy, under construction in the northern and southern...
We have witnessed the detection of what has been recorded has the most energetic Gamma-Ray Burst (GRB) ever: GRB 221009A, also known as the B.O.A.T. (brightest of all time, with $\mathrm{E}_{\mathrm{iso}} \sim 10^{55}$ erg). It spans its emission over the whole electromagnetic spectrum, up to the very high energy (VHE) gamma-ray band: in particular the LHAASO observatory, in China, has been...
Multimessenger astrophysics relies on multiple observational data channels, requiring efficient methods to analyze events of astrophysical origin. Given the increasing volume and complexity of data from modern observatories, machine learning techniques have become essential for efficiently identifying signals.
This project applies machine learning techniques to time series data from the...
KM3NeT is a deep-sea telescope aimed at detecting neutrinos. It is composed of two instruments: ARCA and ORCA. ARCA is mainly aimed at searching for astrophysical sources of TeV-PeV neutrinos, while ORCA is mainly dedicated to the study of neutrino oscillations. Despite their different goals, both instruments can participate in a multi-messenger search by providing information about neutrinos...
Gamma-ray observations of astrophysical neutrino sources are fundamentally important for understanding the underlying neutrino production mechanisms. We investigate the Cherenkov Telescope Array Observatory (CTAO) prospects for detecting the very-high-energy (VHE) gamma-ray counterparts to neutrino-emitting extragalactic sources. The performance of CTAO under different configurations...
Core Collapse supernovae are among the most interesting source of possible multimessenger detections, given the joint production of electromagnetic, neutrino and gravitational waves (GW). In this work we investigate the correlation of SASI structure of neutrino and GW to enhance the GW detection. We compare different search analyses for the case of a benchmark three-dimensional CCSN simulation...
We investigates the accretion of neutron stars (NSs) in active galactic nucleus (AGN) accretion discs. We classify potential accretion modes of NSs in AGN discs, proposing a hierarchical model of NS accretion: accretion flow from the Bondi sphere to accretion columns. The accretion of NSs in AGN discs differs from that of BHs, especially within the scale of the NS’s magnetosphere due to its...
Prompt emission of GRB is believed to be produced from electrons accelerated up to non thermal energies in the internal shocks. This emission peaks in the keV-MeV energy band, but a high energy (HE, 0.1 < E <100 GeV) component is theoretically expected. While photons in the very high energy (VHE; E > 20GeV) domain have been detected by Imaging Atmospheric Cherenkov Telescopes in recent years,...
I will present a summary of observations of active galaxies from the Imaging X-ray Polarimetry Explorer (IXPE). For radio quiet AGN such as NGC 1068 and the Circinus Galaxy, X-ray polarization results from scattering from the corona above the disk or from the inner wall of a molecular torus. Blazars whose synchrotron spectra peak at high frequencies (in or near the X-ray band), denoted as...
Polarimetry is a very important probe of the high-energy processes in the Universe. In December 2021 NASA launched the Imaging X-ray Polarimetry Explorer - IXPE, offering us a completely new window to the Universe, and the tools to study astrophysical systems from a radically different perspective. I will discuss the lessons learned from IXPE's two-year nominal mission and the implications for...
X-ray Quasi-Periodic Eruptions (QPEs) are high-amplitude bursts of X-ray radiation recurring every few hours and originating near the central black holes in galactic nuclei of low-mass galaxies. So far, only a handful of such events has been found. Some of the latest models suggest that these eruptions are triggered by extreme mass ratio inspirals (EMRIs), in which the secondary body interacts...
The radiation produced by the accretion of matter onto supermassive black holes exhibits stochastic flux variations across a range of timescales. These fluctuations offer critical insights into the geometry and physical conditions of the accretion flow as well as the interplay between the different energy emitting regions. In this presentation I will focus on the X-ray flux variability of AGN...
On April 10th, 2024 the second part of the fourth observing run (O4b) started with the detectors Advanced LIGO and Advanced Virgo resuming data taking. The run is ongoing and it is currently planned to end in June 2025.
In this talk, I will highlight the series of installed upgrades on Advanced Virgo plus since the end of the O3 observing run in view of O4. Moreover, I will focus on what...
The fourth observing run (O4) of LIGO-Virgo-KAGRA is ongoing, relying on the most sensitive network of gravitational-wave interferometers to date. In this talk, I will highlight some of the most recent astrophysical findings and their implications (in a multi-messenger context) for massive-star evolution, supernova theory, compact binary populations, and electromagnetic and cosmic-ray...
Black hole mergers, involving masses of tens to hundreds of solar masses, are believed to frequently occur within the accretion disks of central supermassive black holes, potentially producing observable electromagnetic counterparts. These counterparts understood as short flares, can last several days to weeks. Here, we present our initial results on the theoretical modelling of light curves...
Intermediate synchrotron-peaked BL Lacs (IBLs) are quite rare sources in the TeV gamma-ray sky. The IBL B2 1811+31 (z = 0.117) underwent a period of flaring activity in 2020. Detailed characterization of the broad-band emission of the source was achieved thanks to a multi-wavelength (MWL) campaign triggered by the Large Area Telescope (LAT) on board the Fermi satellite in the high-energy...
PG 1553+113 is a high-frequency peaked BL Lac object with a redshift of 0.433, detected by the current generation of Imaging Atmospheric Cherenkov Telescopes up to approximately 1 TeV. Interestingly, the continuous gamma-ray light curve recorded by Fermi-LAT since 2008 has shown a periodic modulation of 2.18 ± 0.08 years at energies above 100 MeV and 1 GeV. Additionally, the source displays...
The flat spectrum radio quasar OP 313 showed extremely intense $\gamma$-ray activity from November 2023 to March 2024, as observed by the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. This initiated a large number of follow-up campaigns at all wavelengths, resulting in a confirmation of the increase of the source activity from the radio to very high energy (VHE) bands....
The Fermi Gamma-Ray Space Telescope has been operational for almost 16 years. During this period, the Fermi Gamma-Ray Burst Monitor (GBM) has been the most prolific Gamma-Ray Burst (GRB) detector ever, with more than 3700 observed GRBs to date. Tens of dedicated single-GRB publications and several general catalogs helped shedding light on the temporal and spectral characteristics of these...
I will explore the dynamics of objects orbiting black holes, focusing on when these dynamics remain regular and when they transition into chaotic behavior. The phenomenon of chaotic dynamics around black holes presents rich and complex behavior, which I will discuss across various scenarios, including both general relativity and modified gravity theories [1,2]. While point-particle dynamics...
Among astrophysical gravitational waves sources yet undetected, of great interest are the binary close encounters involving black holes and/or neutron stars. These systems are characterized by high orbital eccentricities and form via dynamical interactions in dense stellar environments, like globular clusters or Active Galactic Nuclei disks. Their detection could shed light on the different...
In 14 years of operation the Fermi-LAT detected more than 7000 γ-ray sources, of which one third are still not associated with counterparts in other wavelengths, and approximately one fifth are associated with blazar of unknown type. We developed a machine learning method based on an artificial neural network trained with multi-wavelength data which we used to classify blazars of unknown...
The gravitational-wave (GW) cosmology community has been developing techniques and methodologies to infer the cosmological parameters and investigate the black hole population with Compact Binary Coalescences (CBCs) without an electromagnetic counterpart, commonly referred to as dark sirens.
In this study, our focus lies on the method based on galaxy catalogs such as GLADE+, a composite...
The joint detection of a gravitational wave (GW) signal and a short Gamma-Ray Burst (GRB) from a binary neutron star merger in 2017 proved that short GRBs are multi-messenger sources. It is thus fundamental to understand and model the afterglow emission of short GRBs in order to improve our follow-up strategies for detecting the electromagnetic counterparts of GW events. It is widely accepted...
Understanding the interaction of massive black hole binaries with their gaseous environment is crucial since at sub-parsec scales the binary is too wide for gravitational wave emission to take over and to drive the two black holes to merge.
Furthermore the presence of a gaseous disc around sub-pc massive black hole binaries can trigger electromagnetic emission that can be detected by the...
Compact symmetric objects (CSOs) are sources with radio lobe emission on both sides of an active nucleus and an overall size of less than one kpc.
From the detection of 3 CSOs by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope, we know that the emission from these objects can extend into the GeV band. Surprisingly, the first LHAASO catalog reported a TeV source,...
Photons, neutrinos, gravitational waves and cosmic rays may originate from the same source regions, so a multi-messenger approach is crucial for a better understanding of the physics behind the production and propagation of these messengers. In this context, the Pierre Auger Observatory plays a key role to investigate the highest-energy primary particles, given its ability to distinguish...
The Dark Matter Particle Explorer (DAMPE) is a satellite-based detector designed for precise Galactic cosmic ray studies and indirect dark matter search. Since its launch in December 2015, DAMPE has been continuously collecting data on high-energy cosmic particles, with excellent statistics and particle identification capabilities, thanks to a large geometric factor and a good energy...
Quasi-periodic eruptions (QPEs) are recurrent X-ray bursts observed in active galactic nuclei, characterized by regular flares followed by periods of quiescence. One potential explanation for these eruptions involves extreme mass ratio inspirals (EMRIs), where a stellar-mass compact object, such as stellar mass black hole, spirals into a supermassive black hole (SMBH). During it orbit, the...
In this invited talk I will give an overview of current efforts top detect “long-period” (decades or longer) supermassive black hole binaries using optical spectroscopy. Such objects are interesting for many reasons including, but not limited to, (a) they provide tests of models for galaxy evolution through mergers, (b) they make up the population of supermassive black holes producing the...
I will present a novel framework designed to assess the background count rate for spaceborne high-energy detectors—a critical step in identifying faint astrophysical transients. The approach integrates a neural network to estimate background light curves across various timescales and leverages a rapid change-point and anomaly detection technique, Poisson-FOCuS, to flag statistically...
In this contribution, we present several Deep Learning (DL) models developed for high-energy astrophysics to detect and localize gamma-ray transient sources, such as gamma-ray bursts (GRBs). These models were applied to high-energy projects including AGILE, COSI, and CTAO.
AGILE is a high-energy astrophysics space mission launched in 2007, which concluded operations in 2024. Its payload...
Supermassive black hole binaries are thought to be an inevitable product
of the prevailing galaxy evolution scenarios where most massive galaxies
host a central black hole and undergo mergers over cosmic time. The early
stages of this process have been observed in the form of interacting
galaxy pairs and widely separated dual quasars, but the close,
gravitationally bound binaries that are...
We will dive into recent AI advancements for data reconstruction and analysis with spaceborne instruments at the mult-TeV energies. First, we will briefly describe the DAMPE and HERD missions - state-of-the-art spaceprobes for high-energy cosmic rays and gamma-ray physics. Then we will discuss how modern Deep Learning methods broaden the science program of such experiments and even facilitate...
In recent years multifrequency polarimetry is emerging as a powerful tool for investigating blazar jets, especially with the advent of the Imaging X-ray Polarimetry Explorer (IXPE) space observatory.
We study the polarization of High-Synchrotron Peaked (HSP) blazars, where both optical and X-ray emission are due to synchrotron radiation from a population of non-thermal electrons. We adopt an...
With an increasing number of observatories making their data publicly available, we have truly reached the era of multi-wavelength astronomy. Combining gamma-ray data from multiple instruments as well as with measurements at other wavelengths is needed to unlock the data's full potential. However, lack of standardization as well as unique challenges of each instrument can make combining data...
The detection of a double-peaked broadband spectral energy distribution in the long GRB 190114C highlights the need for a systematic study of Gamma-Ray Burst (GRB) temporal and spectral evolution. This study will examine multi-wavelength observations of GRB afterglows, analysing their spectral evolution across seven orders of magnitude in energy, ranging from 0.3 keV to 107 keV. The sample...
