While the existence of a diffuse flux of high-energy astrophysical neutrinos has been established for over a decade, the sources of this signal still need to be discovered. Last year, the IceCube Collaboration reported evidence for TeV neutrinos from the nearby active galaxy NGC 1068 at 4.2 sigma. After the blazar TXS 0506+056, NGC 1068 is the second extragalactic neutrino source identified....
Massive black hole (MBH) binaries are among the loudest expected sources of low frequency gravitational waves. The rate of MBH coalescences is still very uncertain, and EM observations of close MBH binaries have the potential to strongly reduce the current uncertainties. I will discuss the physical consequences of the presence of a binary on the surrounding gas, deriving the observational...
A tidal disruption event (TDE) occurs when a star is destroyed by the strong tidal shear of a massive black hole (MBH). TDE detections can unveil otherwise dormant MBHs, and they constitute unique probes for constraining the MBH demographics, especially towards the low-mass end of the MBH mass function. In order to do so, it is fundamental to theoretically constrain the expected TDE rates...
X-ray quasi-periodic eruptions (QPEs) are a new variability phenomenon observed around low-mass ($M_{BH} < 10^7\,M_{\odot}$) supermassive black holes. They appear as sharp and intense bursts of soft X-ray emission ($E < 2$ keV), that last about one hour and repeat quasi-periodically every few hours. Each QPE emits a luminosity of $10^{42-43}$ erg s$^{-1}$, typically one order of magnitude...
I compare two versions of the analysis of the gravitational wave signal GW150914 presented previously by the LIGO/Virgo collaboration (LVC). The first version was presented in 2016 by this collaboration along with their announcement of the first experimental detection of gravitational waves [1]. It was based on rigorous general-relativistic treatment of the coalescing two-body problem. The...
The new data release four (DR4) of the Fourth catalog of gamma-ray sources of the Fermi Gamma-ray Space Telescope Large Area Telescope (4FGL), is based on gamma-ray photons detected with energy between 50 MeV and 1 TeV, and accumulated during the first 14 years of the Fermi all-sky survey. The analysis methods are inherited from the first 4FGL catalog (8-year list), with several new features...
Although there is indirect experimental evidence on the existence of dark matter, the debate on its nature is still open. One class of possible candidates is represented by Weakly Interacting Massive Particles (WIMP).
Our galaxy is largely composed of Dark Matter. Assuming that pairs of WIMPs can annihilate to produce gamma rays, or that WIMPs can directly decay into photons, monochromatic...
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. Astrophysical and cosmological signatures of axion-like particles might be found in many observations, including gravitational wave spectra, but most importantly in the...
Follow-up of gravitational wave alerts has proven to be challenging, primarily due to the large uncertainty on the localisation, which is often significantly larger than the field of view of most instruments. A smart pointing strategy significantly enhances the chance of rapidly observing the true position of the underlying compact binary merger event and so to detect an electromagnetic...
Despite the increasing number of GW detections, the astrophysical origin of the Binary Black Hole (BBH) mergers detected by the LIGO and Virgo interferometers remains elusive. A promising formation channel for these BBHs is inside accretion discs around supermassive black holes, that power AGN. Investigating the spatial correlation between the positions of these potential host environments and...
Tidal disruption events (TDEs) are bursts of electromagnetic energy released when supermassive black holes (SMBHs) at the centers of galaxies violently disrupt a star that passes too close. TDEs provide a new window to study accretion onto SMBHs and may be associated with high energy neutrinos. In some rare cases, this accretion leads to launching of a relativistic jet, but the necessary...
The study of cosmic-ray accelerators is done with a multi-wavelength approach which provides a more complete view of the physical phenomena that involve the acceleration of charged particles. Cosmic-ray accelerators are both galactic, for example Supernova Remnants, and extragalactic, for example Active Galactic Nuclei and Gamma-Ray Bursts. To get a larger sample of Galactic cosmic-rays,...
In this contribution we present the analysis of GRB221009A, the brightest Gamma-Ray Burst (GRB) ever detected by the Fermi Large Area Telescope (LAT). The burst triggered the Gamma-Ray Burst Monitor (GBM), and the high-energy emission of the triggering pulse started in the LAT before the associated low-energy component detected by the GBM. During the prompt phase, we identified a Bad Time...
GRB 221009A is an exceptionally bright gamma-ray burst (GRB) that reached Earth on 2022 October 9th after traveling through the dust of the Milky Way. The Imaging X-ray Polarimetry Explorer (IXPE) pointed at GRB 221009A on October 11th and measured, for the first time, the 2-8 keV X-ray polarization of both a GRB afterglow and rings of dust-scattered photons which are echoes of the GRB prompt...
As the most energetic explosions in the Universe, long-duration Gamma-ray Bursts (GRBs) provide a unique opportunity to explore physics at extreme energy scales that are otherwise impossible to investigate in Earth-bound laboratories. The radiation produced by the interaction of their ejecta with the environment contains clues to their progenitors and to the mechanisms responsible for...
The brightest long gamma-ray burst (GRB) detected so far by the \textit{Swift}-BAT and \textit{Fermi}-GBM telescopes, GRB~221009A, provides an unprecedented opportunity for understanding the high-energy processes in extreme transient phenomena. We find that the conventional leptonic models for the afterglow emission from this source, synchrotron and synchrotron-self-Compton, have difficulties...
The duration distribution of gamma-ray bursts is bimodal, and the general consensus has been that the two groups stem from separate progenitors: binary compact object mergers and supernovae for short and long GRBs, respectively. A number of events discovered in the recent past has however proven this distinction to be imperfect. Kilonovae, the smoking-guns of mergers, were detected following...
The origin of gamma-ray bursts (GRBs) is still mysterious. We believe that binary neutron star (BNS) mergers produce short GRBs, while long GRBs are associated to the collapse of massive stars.
This GRB dichotomy, based on the duration of the prompt pulse, was recently challenged by the detection of the bright and relatively close (z=0.076) GRB 211211A. Despite its long duration (~30 s), the...
The merger rate density of binary compact objects and the properties of their host galaxies carry crucial information to understand the sources of gravitational waves. In this talk, I present galaxyRate, a new code that estimates the merger rate density of binary compact objects and the properties of their host galaxies, based on observational scaling relations. We generate synthetic...
Binary neutron stars (BNSs) wield a pivotal role in modern astrophysics. Merging BNSs not only can be loud sources of gravitational waves, but also trigger short gamma-ray bursts and kilonovae. A great example of such event is the renowned GW170817; the observation of its electromagnetic counterpart paved the way for new frontiers in multimessenger astrophysics.
Moreover, thanks to the timing...
Pulsars are the largest class of Galactic sources detected by NASA's Large Area Telescope (LAT) on the Fermi mission. Pulsars are generally acknowledged as very stable astrophysical rotators, and they gradually slow down by emitting radiation at the expense of their rotational energy. Occasionally, pulsars can undergo transient events called glitches, which consist in rapid changes in their...
W44 is a middle-aged Supernova Remnant (SNR) largely investigated to probe acceleration of Cosmic Rays (CRs). Previous studies already showed the presence of gamma-ray emission not only from the remnant, but also from its surroundings, thought to be due to high-energy CRs escaping from the forward shock of the remnant.
We present a detailed morphological and spectral analysis of Fermi-LAT...
GW170817 is an outstanding event as it paved the way for multi-messenger astrophysics. It is a binary neutron stars merger, that saw the detection of a gravitational wave (GW), a gamma ray burst (GRB) and an afterglow. Such events are interesting also from a cosmological point of view, as we can derive an Hubble constant ($H_0$) measurement (the current expansion rate of the Universe),...
GRB absorption spectra are powerful probes of the circumburst medium of their progenitor and the host galaxy's ISM. The column densities as derived from the X-ray and the optical spectra differ by up to an order of magnitude, suggesting the presence of a highly ionised region close to the GRB. This happens because the X-ray absorption probes the total column along the line of sight, including...
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 component is theoretically expected. While photons in the very high energy domain have been detected by Cherenkov Telescopes in recent years, prompt-related VHE photons have not been observed yet....
The rare multimessenger event GW170817 showed a new way of making cosmology with the potential to resolve the tension between different measurements of the expansion rate of the Universe given by the Hubble constant.
However, most of the detected gravitational wave signals from compact binaries up to date do not have a multi-messenger counterpart, earning them the designation of dark...
Molecular clouds in the Galactic Centre will glow in neutrinos and gamma-rays when bombarded by energetic hadrons. Gamma-ray imaging of the Galactic Centre has therefore been employed to study the cosmic-ray energy spectrum and density distribution around Sgr A*. While part of the gamma-rays may be contributed by leptons, leading to uncertainty that is challenging to estimate, neutrinos serve...
The huge luminosity, the redshift distribution extending at least up to z~10 and the association with the explosive death of very massive stars make long GRBs extremely powerful probes for investigating the early Universe (pop-III stars, cosmic re-ionization, SFR and metallicity evolution up to the “cosmic dawn”) and measuring cosmological parameters. At the same time, as demonstrated by the...
I will present an update on the HERMES Pathfinder + SpIRIT projects, currently in phase-D. These projects are in-orbit demonstrations, with the goal of demonstrating that Gamma Ray Bursts can be efficiently observed and localized by miniaturized instrumentation hosted by CubeSats. This can allow the design and implementation of a sensitive all-sky, all-time X-ray/Gamma-ray observatory, based...
The KM3NeT collaboration is building two underwater neutrino detectors in the Mediterranean: the ARCA (Astroparticle Research with Cosmics in the Abyss) and ORCA (Oscillation Research with Cosmics in the Abyss) detectors.
ARCA is located off the Sicilian coast of Capo Passero and aims to detect and identify astrophysical neutrino sources. The ORCA detector, located off the French coast of...
The detection of gravitational waves in 2015, thanks to the LIGO and Virgo interferometers, opened a new window on our Universe. The discoveries during the first three observing runs already had an extraordinary impact on astrophysics, cosmology, and fundamental physics.
The GW community is now looking at the next long–prepared step: ‘third–generation’ detectors. Thanks to an increase of...
The Virgo and LIGO instruments and their first observations are amazing, but they are only the very first step into the new era of GW science and astronomy. The prospect to detect signals from kilometer-scale sources out to redshifts of 100 with the proposed Einstein Telescope and Cosmic Explorer, or the merger of massive black holes with LISA is mind-boggling. These detectors are part of a...
In this talk, I will first give a brief update on the the Laser Interferometer Space Antenna mission status. Afterwards, I will review the different ways in which electromagnetic and gravitational wave information are synergistically used to gather unique scientific inshight into the variety of sources present in the LISA Gravitational wave band. Broadly speaking these are divided in two...
The Compton Spectrometer and Imager (COSI) is a gamma-ray telescope, selected by NASA as a Small Explorer satellite mission to be launched in 2027. COSI employs a novel Compton telescope, consisting of a compact array of cross-strip germanium detectors. Owing to its wide field-of-view and excellent energy resolution, COSI will achieve an unprecedented sensitivity in the 0.2-5 MeV energy band....
The detection of the gravitational wave (GW) signal GW170817 and the electromagnetic (EM) signal AT2017gfo confirmed the association between binary neutron star (BNS) mergers and kilonovae (KNe) and showed the potential of joint detection to unveil the nature of neutron stars and the nucleosynthesis of heavy elements in the Universe. The next-generation GW interferometers, such as the Einstein...
The Vera Rubin Observatory will be a powerful instrument in the discovery and follow-up of kilonovae (KNe), especially in the perspective of third generation gravitational wave (GW) observatories which will come online towards the end of the tenure of Rubin's decadal survey (LSST WFD) in the mid 2030s. Follow-up of electromagnetic (EM) counterparts of binary neutron star (BNS) mergers provides...
The Einstein Telescope (ET) will be an innovative next generation gravitational wave (GW) interferometer. With ET it will be possible to explore a large volume of the Universe and detect thousands of binary neutron star systems mergers (BNS) per year. The corresponding electromagnetic (EM) counterparts will likely be faint and to be searched in the large error regions of ET GW signals. Beyond...
The production of VHE early emission of gamma‑ray bursts (GRBs) is still highly debated. Nowadays, we mostly rely on observations in the range of 10 keV-10 MeV while at higher energies (above 100 GeV), the current instruments have difficulties due to time spent repositioning the telescope. I will discuss the multi-messenger observational strategies to detect the early emission of short GRBs...
SVOM is a joint French-Chinese mission dedicated to the study of gamma-ray bursts (GRBs) and high-energy transients. SVOM boasts a suite of space-based instruments spanning from hard X-rays to visible light that will be complemented by a ground segment of optical telescopes. With an expected launch in early 2024, SVOM will also contribute to multimessenger observations of gravitational waves...
