Invited Speakers

Giancarlo Ghirlanda
INAF-Osservatorio Astronomico di Brera

The structure of Gamma Ray Burst jets.

The structure and orientation of gamma-ray burst jets, due to relativistic bulk motion of the outflow within the jet, have a fundamental role in determining how they appear. The discovery of the GW170817 and the associated short GRB boosted theoretical studies on the origin of jet structure and the search for observational features supporting the presence of a quasi universal jet structure. The jet structure is the outcome of a series of complex processes that involve the central engine that powers the jet and the interaction of the latter with the progenitor's material. Key signatures of the possible presence of a structured jet in GRBs can be found in the prompt and afterglow emission properties and are highlighted by population studies.

Dafne Guetta
Ariel University, Ariel, Israel

On the hadronic origin of the TeV radiation from GRBs and the expected neutrino flux.

The recently discovered TeV emission from Gamma-Ray Bursts (GRBs) hints towards a possible hadronic origin of this radiation component. To investigate such scenario, we developed a tailored Monte Carlo (MC) simulation that reproduces the kinematics of photo-hadronic interactions occurring at internal shocks, including the electromagnetic cascade process that the resulting secondary gamma rays undergo inside the GRB jet. As a result, we find that sub-TeV observations of GRB190114C can be reproduced by a baryonic energy content comparable to that in sub-GeV photons and a bulk Lorentz factor Gamma ~50. Neutrino flux predictions are found to be consistent with experimental upper limits set by ANTARES and IceCube.

Maria Grazia Bernardini
INAF-Osservatorio Astronomico di Brera

Gamma-Ray Bursts central engine in the multi-messenger era.

Multi-messenger Astronomy opened a new discovery window, providing the long-sought smoking gun for short gamma-ray burst (GRB) progenitors, almost 20 years after the discovery that long GRBs are originated in the collapse of massive stars. Despite these many advancements in the field, the nature of the remnant compact object that powers both long and short GRBs is still unsettled. Currently, newly-born millisecond magnetars are competing with black holes as source of the GRB power, mainly with their rotational energy reservoir. In this talk we review the main observational evidences supporting the two scenarios, and we discuss how the combined information provided by both the electromagnetic and gravitational signals are the most promising way to unveil the nature of the central engine, that is one of the major breakthrough achievable with the next generation gravitational wave detectors.

Samuele Ronchini

Perspectives for multi-messenger astronomy with the next generation of gravitational-wave detectors and high-energy satellites.

The Einstein Telescope (ET) is an ambitious project for the future of multi-messenger astrophysics and the optimisation of the synergy with astronomical facilities is a cardinal point which needs to be addressed. In order to detect the counterparts of binary neutron star (BNS) mergers at high redshift, the observation of high-energy signals will play a crucial role. I will show the predictions of the high-energy emission of BNS mergers and its detectability in a theoretical framework based on a universal jet structure and able to reproduce the properties of the current sample of short gamma-ray bursts (GRBs). The joint gravitational-wave and high-energy detection rate is estimated for both the prompt and afterglow emissions, testing several combinations of instruments and with the aim of determining the best observational strategies. I will finally emphasise the crucial role of future wide field X-ray missions for the identification and localisation of the EM counterpart.

Andrea Sanna
Università di Cagliari

On the localisation capabilities of the HERMES + SpIRIT constellation of cube-sats.

The association of GW170817 with GRB170817A proved that electromagnetic counterparts of gravitational wave events are the key to deeply understanding the physics of NS-NS merges. Upgrades of the existing GW antennas and the construction of new ones will increase sensitivity to several hundred Mpc, vastly increasing the number of possible electromagnetic counterparts. Monitoring of the hard X-ray/soft gamma-ray sky with good localization capabilities will help to effectively tackle this problem allowing to fully exploit multi-messenger astronomy. However, building a high-energy all-sky monitor with a large collective area might be particularly challenging due to the need to place the detectors onboard satellites of limited size. Distributed astronomy is a simple and cheap solution to overcome this difficulty. Here we discuss dedicated timing techniques that allow precise localization of astronomical events in the sky, taking advantage of the spatial distribution of the HERMES Pathfinder and SpIRIT swarm of detectors orbiting Earth.

Lorenzo Amati
INAF - OAS Bologna

The Amati relation after 20years: discovery, main properties, most relevant applications and perspectives.

Discovered exactly 20 years ago (Amati et al., A&A 2002, most cited article among those reporting results from the BeppoSAX mission), the correlation between spectral peak energy, Ep,i , and isotropic-equivalent total radiated energy, Eiso, referred to as "Amati relation" in the scientific literature, is one of the most relevant and investigated properties of Gamma-Ray Bursts (GRBs), with strong implications for prompt emission physics, identification and understanding of different sub-classes, using these phenomena for measuring cosmological parameters. I will review the observational status of the Amati relation, its main properties and consequences, the expected developments from near future (e.g., SVOM) and next generation (e.g., THESEUS, HERMES) space missions dedicated to GRBs.

Jorge Armando Rueda Hernandez

White dwarf binary mergers: an overlooked class of low-energy gamma-ray bursts.

White dwarf binary mergers (WD-WD) are numerous sources that can lead to the formation of neutron stars (including magnetars) or type Ia supernovae. I will show that the overlooked WD-WD avoiding the above two fates can lead to gamma-ray bursts with a precursor, prompt, and afterglow emission across the electromagnetic spectrum from the radio to the gamma-rays. I also discuss the detectability of the above emissions by current and forthcoming detectors, including the associated gravitational-wave emission.

Paolo D'Avanzo
INAF-Osservatorio Astronomico di Brera

Short Gamma-ray bursts in the multi-messenger era: situation and perspectives.

The knowledge of short gamma-ray bursts (SGRBs) experienced an impressive boost in the past two decades. After the recent major breakthroughs, we now have direct evidence for: the NS-NS / SGRB association, the existence of NS-BH systems, SGRB outflows shaped as structured jets, off-axis afterglow emission, the existence of r-process kilonovae and their association with SGRBs. The majority of the studies on SGRB properties reported in the literature are based over the sample of events with measured redshift (z). Although this approach has the advantage of describing the SGRB intrinsic properties, it can be affected by biases, given that almost 3/4 of SGRBs are lacking z. With the aim of overcoming this issue, in 2014 we presented a sub-sample of Swift SGRBs with favorable observing conditions for z determination and bright in in the 15–150 keV Swift-BAT energy band. Although relatively small (16 events up to Jun 2013), this sample (S-BAT4) is complete in flux with a high completeness in z (70%), providing a useful bench to study the SGRB properties. The sample has recently been extended, being now more than double in size (42 events up to Dec 2021), keeping high completeness in z (60%). In this talk I will review the situation and perspectives of our understanding of SGRBs, their progenitors and their association with kilonovae and GWs, and will discuss how the S-BAT4 sample can represent a robust base for SGRB studies.

Riccardo Ciolfi
INAF, Osservatorio Astronomico di Padova

From binary neutron star mergers to short gamma-ray burst jets: towards the first end-to-end numerical modelling.

The multimessenger observation of a binary neutron star (BNS) merger in 2017 confirmed that such systems can launch powerful jets and produce short gamma-ray bursts (SGRBs). Modelling the involved physical processes via numerical simulations is however extremely challenging. Despite great advancements in general relativistic MHD simulations of BNS mergers over the last decade, the jet formation mechanism and the nature of the central engine remain unclear. Moreover, the incipient jet propagation across the post-merger environment and up to the electromagnetic emission scales has been so far modelled separately from the merger process, without a consistent end-to-end description. In this talk, I will review recent developments in simulations of BNS mergers, jet launching, and jet propagation up to a nearly ballistic expansion, and show how the different scales and evolution phases can be combined in a unified model. I will then conclude with future prospects and upcoming challenges.

Gor Oganesyan

Physics of the GRB prompt emission.

Gamma-ray bursts (GRBs) are keV-MeV transients that show sub-second variability and usually described with non-thermal spectra. Despite the simplicity of the observed GRB spectra composed typically by two power-laws, it is quite challenging to account for their spectral shape in the standard dissipation and radiation scenario. I will discuss the novel spectral feature that is found in the X-ray domain. Recent discovery of the hardening of the GRB spectra at the lower energies indicated the synchrotron origin of the emission. At the same time, it causes new theoretical challenges which require the emitting particles to cool only marginally. I will discuss the recently proposed scenarios to account for the low-energy spectral breaks. I will also discuss the future prospects by observing the prompt emission in the very-high-energy gamma-rays (E > 50 GeV) by CTA and by the upgraded high-energy neutrino observatory, IceCube Gen 2.

Andrea Rossi
INAF-OAS Bologna

The hunt for GRB host galaxies.

The search of GRB host galaxies helps measure the redshift of GRBs even when it is not possible to determine it from the afterglow because of its faintness or undetected clear absorption lines. The redshift allows us to determine the prompt properties of GRBs and their afterglows. In the case of long GRBs (lGRBs) and their association to massive stars, study of their hosts showed that they prefer low-mass star-forming galaxies with sub-solar metallicity, and can trace the evolution of the cosmic star-formation rate, though very peculiar cases exist. Long and short GRBs however differ in several aspects. Short GRBs (sGRBs) and their afterglows are fainter, which is somewhat similar to the case of dark GRBs. However, sGRBs have larger offsets from their hosts, too. This is indirect evidence of their origin from an old stellar population that migrated far from its formation region. Both faintness and large offsets makes the search for sGRB hosts much difficult or even impossible. Nevertheless, thanks to an enormous observational effort, we have today an understanding of the sGRB host population which is comparable to that of lGRB hosts.

Stefano Ascenzi
Institute of Space Sciences (ICE) - CSIC-IEEC

The origin of the X-ray plateaus in the structured jet scenario.

The X-ray emission of gamma-ray burst (GRBs) is often characterized by an initial steep decay followed by a nearly constant emission phase (so-called "plateau") which can extend up to thousands of seconds. While the steep decay is usually interpreted as the tail of the prompt gamma-ray flash, the long-lasting plateau is commonly associated with the emission from the external shock sustained by energy injection from a long-lasting central engine. Recently, different models have been proposed, which ascribe the origin of the plateau to the structured nature of the GRB jet, without requiring any assumption about the central engine. In this talk I will review these models, focusing in particular on the high-latitude emission model, which associates both the early steep decay and the plateau with the prompt gamma-ray emission. I will also show that even when the GRB is observed off-axis this model predicts a bright X-ray transient, which can constitute an interesting target for follow-up observational campaigns of gravitational wave events.


Contributed Talks

Riccardo Crupi
Università di Udine

A data driven framework for searching long faint astronomical high-energy transients.

We present a new tool to estimate the background, a key step to allow sensitive searches for excesses due to cosmic transients. We employ a Neural Network (NN) to estimate the background light curves on different timescales. We employ subsequently a fast change-point and anomaly detection technique to isolate observation segments where statistically significant excesses in the observed count rate relative to the background estimate exist. We test the new software on archival data from the NASA Fermi Gamma-ray Burst Monitor (GBM), which has a collecting area and background level of the same order of magnitude to those of HERMES pathfinder. The neural network performances are discussed and analyzed over period of both high and low solar activity. We were able to confirm events in the Fermi GBM catalog (both solar flares and Gamma Ray Bursts, GRBs), and found events, not present in Fermi GBM database, resembling solar flares, terrestrial flashes, GRBs.

Lorenzo Cavallo
Università degli Studi di Padova

On the hosts of neutron star mergers in the nearby Universe.

With the advent of multi-messenger astrophysics, the characterisation of binary systems of neutron stars has become central in various fields. In this work, we explore possible observational proxies that can be used to infer the delay time distribution (DTD) of neutron star mergers (NSMs). To do that, we construct a sample of model galaxies that fulfils the observed mass distribution function, star formation rate versus mass relation, and the cosmic star formation rate density. The star formation history of these galaxies is described with a log-normal function. For the NSMs, we assume a theoretical DTD that mainly depends on the lower limit and the slope of the distribution of separation of the binary neutron stars (NS) systems at birth. We find that the current local rate of NSMs requires that ~0.3 per cent of NS progenitors lead to a NSM within a Hubble time. The fraction of short-GRBs observed in late-type galaxies favours DTDs with a fair fraction of prompt events.

Andrea Rossi
INAF-OAS Bologna

Mixing up the standard GRB classification.

The recent years brought us new peculiar and surprising GRBs. First, the peculiar GRB 200826A was a short gamma-ray burst (sGRB) for which our analysis revealed an optical and NIR bump in the light curve whose luminosity and evolution is in agreement with several longGRB-SNe. On the opposite side, GRB 211211A was by definition a long GRB, but our optical/NIR observing campaign showed that it was associated with a kilonova, implying that the progenitor was a compact object merger. Finally, the GRB 210905A was a rare very high redshift z=6.312, with an extremely luminous burst and afterglow. Despite these results, our findings demonstrate that the overall properties of this burst are in agreement with those of less distant burst. These finding have shown us that GRB observations are continuously providing new constraints on their origin. Future GRB dedicated missions in synergy with gravitational wave interferometers, are crucial to increase our understanding of these events.

Giuseppe Dilillo

Algorithms for Gamma-Ray Bursts detection.

Algorithms for detecting gamma-ray bursts (GRB) have gone largely unchanged through 50 years of observations. Today, robust anomaly detection techniques exist which can serve as the foundation for a more sensible and efficient algorithm standard. We discuss the limitations of the conventional approach and the application of a novel changepoint detection technique called FOCuS to the problem of detecting gamma-ray bursts. Performances of different algorithmic strategies are assessed and compared, both on synthetic and real-world data, targeting metrics such as computational efficiency and rate of false or missed detections.

Stefano Giarratana
University of Bologna-INAF/IRA

GRB 201015A: a relatively faint GRB with a hint of Very High Energy gamma-ray emission.

A total of four GRBs have been confirmed at very high-energy (> 100 GeV; VHE) with high significance so far, and any possible peculiarities of these bursts will become clearer as the number of detected events increases. In fact, it is not clear whether the VHE photons are produced through synchrotron emission, synchrotron self-Compton or from external inverse-Compton yet. Multi-wavelength follow-up campaigns are required to extract information on the physical conditions within the jets that lead to the VHE counterpart, hence they are crucial to reveal the properties of this class of bursts. In this talk I will present the results from a multi-wavelength (from X-rays to radio), multi-scale (up to milli-arcsec resolution) follow-up campaign of GRB 201015A, the possible fifth VHE GRB (z = 0.426): we studied the GRB emission with the standard fireball model and we derived constraints on the possible jet proper motion (off-axis event) or expansion of the outflow (on-axis GRB).

Francesco Longo

High Energy emission from GRBs, from Fermi to IACTs.

A new era in the understanding of Gamma Ray Bursts (GRBs) has started with the discovery of the Very High Energy emission from Gamma Ray Bursts by Imaging Cherenkov Atmospheric Telescopes (IACTs). In this presentation I will review the crucial contributions by the Fermi Large Area Telescope to explore the emission mechanisms by GRBs at the highest energies and its role in the path that led to the discovery of the highest energy components by IACTs. In particular I will present the main results obtained by the LAT on the GRBs properties, as outlined in the second GRB catalog. I will review the delayed and prolonged emission, the spectral characteristics of the prompt and of the delayed phase, the flux and fluence distributions of the LAT detected GRBs. I will also present some key GRBs and their peculiar properties.

Giulia Gianfagna

A simultaneous model fitting of GW and EM data of mergers: breaking model degeneracies in GW170817 and future events.

On August 17th 2017, advanced LIGO and Virgo observed the first gravitational-wave signal from a binary neutron star merger, named GW170817. It was followed by a short duration gamma ray burst and a non-thermal afterglow emission, paving the way for multi-messenger astrophysics. In this work, a combined simultaneous fit of the electromagnetic and gravitational-wave domains is implemented, treating the inclination of the system as shared parameter. The value of the inclination that we recover from this fit is in agreement with the LIGO-Virgo previous works, with an uncertainty that is 10-fold smaller, thanks to contribution of the electromagnetic data. Moreover, with the inclusion of the gravitational-wave data, the degeneracy between the viewing angle and the jet opening angle is broken. We also apply this procedure to a simulated GW170817-like event at larger distance, and find that the gravitational-wave information is fundamental to retrieve the viewing angle.

Martin Topinka

Is rapid optical rise of GRB 190919B a sign of late flaring activity.

The light curve of an optical afterglow of long GRB 190919B detected by INTEGRAL exhibits an unusually steep rise, unexpected from a 'canonical' GRB optical afterglow. This invokes a scenario consisting of two superimposed flares: an optical flare originating from the inner engine activity followed by the hydrodynamic peak of an external shock. The inner-engine nature of the first pulse is supported by a marginal detection of flux in hard X-rays.

Sergio Campana
INAF-Osservatorio Astronomico di Brera

HUGO: the High-redshift Universe GRB Observatory.

The race for the most distant object in the Universe has been played by long-duration gamma-ray bursts (GRBs), star-forming galaxies and quasars. GRBs took a temporary lead with the discovery of GRB 090423 at a redshift z=8.2, but now the record-holder is the galaxy GN-z11 at z=11.0. Despite this record, galaxies and quasars are very faint (GN-z11 has a magnitude H=26), hampering the study of the physical properties of the primordial Universe. On the other hand, GRB afterglows are brighter by a factor of ~100, with the drawback of lasting only for 1-2 d. Here we describe a novel approach to the discovery of high-redshift (z > 6) GRBs, exploiting their nIR emission properties.

Aishwarya Linesh Thakur

Time-evolving modelling for fits to Xray GRB afterglows.

GRB spectra are powerful probes of the circumburst medium of their progenitor and the host galaxy's ISM. The X-ray absorption probes the total column along the line of sight, including the immediate vicinity of the GRB, while optical absorption probes the neutral ISM within the host, providing a complementary window to study the nature of the medium. Additionally, the column densities as derived from the X-ray and the optical differ by up to an order of magnitude, suggesting the presence of a highly ionised region close to the GRB. In this study, we present a combined analysis, with fits to a sample of six GRBs using a newly developed time-evolving photoionisation model in conjunction with the optically derived absorption. We find that our model can successfully fit five bursts, the remaining burst being fully consistent with a neutral medium. We also discuss the implications of our fits and how they can be interpreted in the context of the total column towards the GRB.

Andrea Saccardi
GEPI, Observatoire de Paris, Université PSL, CNRS

Dissecting the interstellar medium of a z=6.3 galaxy. X-shooter spectroscopy and HST imaging of the afterglow and environment of the Swift GRB 210905A.

Long gamma-ray bursts (LGRBs) are unique tools to probe first galaxies. Afterglow spectroscopy allows detailed studies of the properties of the ISM of star-forming galaxies up to the highest redshift. In this talk, I will show the results obtained with VLT/X-shooter observation of the afterglow of GRB210905A at z=6.3118. We detect neutral-hydrogen, low-ionization, high-ionization and fine-structure absorption lines, as well as a tentative Lyman-α emission at velocity > 1000km/s from the absorbing gas. We were able to determine the metallicity, kinematics and chemical abundance pattern, dust depletion and dust-to-metal ratio of the ISM at z=6.3118. We also obtained HST/F140W observations of the GRB field, that allowed us to detect the GRB host galaxy as well as a complex of four objects in the proximity of the GRB afterglow position. These results show the powerful potential of GRBs to access detailed information on the properties of high-redshift galaxies.

Luciano Burderi
Università degli Studi di Cagliari

CubeSats and Distributed Astronomy: from the HERMES fleet to the flight of the ALBATROS, surfing the waves of quantum space-time.

ALBATROS (Astonishingly Long Baseline Array Transients Reconnaissance Observatory in Space) is an ambitious astro- physical mission concept that uses a fleet of three small satellites to create an high-energy all-sky monitor with excellent localisation capabilities. The proposed orbits for the spacecrafts are three independent Earth-trailing heliocentric orbits, that will form a nearly equilateral triangular formation with 2.5 106 km arm length: the so-called cart-wheel formation. Each satellite is equipped with two opposite facing ∼ 500 cm2 effective area detectors each consisting of a segmented array of crystal scintillators (GAGG) with a half-sky Field of View, keV-MeV energy band, and temporal resolution better than one microsecond. Thanks to the million km baselines, temporal triangulation techniques allow unprecedented location accuracies, few arc-second/few arc-minutes, for bright/faint transients in a wide energy band, few keV-few MeV crucial for hunting the elusive electromagnetic counterparts of Gravitational Waves, that will play a paramount role in the future of Multi-messenger Astronomy. This project is an example of high-energy distributed astronomy: a new concept of modular observatory consisting of a fleet of small satellites displaced over a large array, with sub-microsecond time resolution and wide energy band (keV-MeV). A pathfinder of ALBATROS is already under development through the HERMES (High Energy Rapid Modular Ensemble of Satellites) and SpIRIT (Space Industry Responsive Intelligent Thermal Nanosatellite) projects: a fleet of six 3U cube-sats (HERMES) to be launched by the end of 2023 plus one 12U cube-sat (SpIRIT) to be launched by the end of 2022. ALBATROS will furnish the golden sample of GRBs needed to test the dispersion law theorised by some Quantum Gravity theories, which predict relative discrepancies of the speed of photons w.r.t. the speed of light proportional to the ratio of the photon energy to the Planck energy. This effect is extremely small, and GRBs occurring at cosmological distances represent the ideal target to explore it. We describe a compelling approach to this problem that statistically combines a large number of GRBs for which light-curves of the prompt emission over a wide energy band (keV-MeV) are available, and distances are known. We discuss how a golden sample of ∼ 1000 GRBs with known redshift is sufficient to effectively constrain this dispersion law.

Alfredo Luminari

Time Evolving Photoionisation Device (TEPID): a new code for time evolving photoionisation and spectral fitting .

GRBs and their UV/X-ray afterglows are powerful transient sources of ionising radiation. They dramatically modify the state of the surrounding medium, thus enabling its characterization through time-resolved UV and X-ray spectroscopy. This allows to shed light on several elusive GRB properties, such as their metallicity, ejecta, progenitors and, for long GRBs, the surrounding star forming region. The key for this analysis is a time evolving photoionisation modelling, since ionisation patterns from variable sources strongly depend on the lightcurve and the absorbing gas and cannot be mimicked by any of the time-equilibrium models currently available. Here we present our new, fully self-consistent TEPID model, which follows the gas ionisation and temperature in response to any time-variable source of radiation. It computes time-resolved UV and X-ray absorption spectra to be directly compared with observations (eg through XSPEC), thus allowing to constrain the source and gas properties.

Giovanni Della Casa
Università degli Studi di Udine

Study of Gamma-Ray Bursts microvariability.

Entering the multimessenger era, the interest for Gamma-Ray Bursts (GRBs) increases importantly. An important part of the science about GRBs comes from the study of the pulses present in the prompt lightcurve. The time profiles can be very different in the number of pulses and their duration. Consequently, applying a time series analysis, like structure function analyses through Haar wavelets, on those lightcurves can provide important informations about the variability of the GRB prompt emission. The microvariability of a GRB consists in the minimum timescale over which we can observe an important flux variation in the GRB prompt lighcurve. Knowing this minimum variability timescale allows to set important constraints, for example on the central engine dimension. The attempt is to set a clear and solid way to obtain the microvariability, and apply the technique developped over a large number of GRBs from GBM and Beppo-SAX. The results will be presented at the conference.

Ezequiel Marchesini
INAF-OAS Bologna

The X/Gamma-ray Imaging Spectrometer XGIS: Unveiling a high-energy broadband.

The X/Gamma-ray Imaging Spectrometer (XGIS) is one of the instruments onboard the THESEUS mission, which has successfully completed a three-year Phase A study as an ESA-M5 candidate, and is now an M7 mission concept candidate. Profiting from new technology, XGIS will operate in a wide energy band from 2 keV to 10 MeV. XGIS will work with a FoV of 117 × 77 deg2 and with a location accuracy of < 15 arcmin (< 150 keV), and with a FoV of 2 sr (< 10 MeV). It consists of two cameras, each one an ensemble of Siswich detectors working in parallel, achieving a large effective area. The new electronics for this ensemble, the ORION ASIC, allows for a very low-noise and fast readout, with a timing resolution of a few us. With its scientific performance, XGIS will be able to detect all kinds of GRBs, up to very high redshift, and to provide a wide band characterization. Since THESEUS has already completed a Phase A study, a high TRL of its components, including XGIS, can be achieved in a short time.

Riccardo Brivio


In the context of Gamma-Ray Bursts (GRBs), despite several years of observations and a large number of GRBs analysed to date, a unique, general picture describing their physics is still missing: further observations and additional, independent techniques are needed for this purpose. Polarimetry constitutes a really powerful tool since it allows us to investigate some features of the source that are difficult to determine with different techniques, such as the geometry of the emitting region and the local magnetic field configuration. Time-resolved polarimetric analysis of GRB afterglows would allow us to infer these features and the physics behind the event. In addition, spectro-polarimetric analysis can allow us to investigate the spectral dependence of the polarised radiation and to identify possible additional contributions given to the total polarisation by different sources, e.g. interstellar polarisation induced by dust along the line of sight. In spite of its importance in this context, only a handful of bursts detected by space telescopes were accompanied by ground-based spectro-polarimetric follow-up to date. In the talk I will present (spectro-)polarimetric analysis of GRB 080928, an event not yet properly analysed, for which multi-epoch polarimetric observations were obtained. The analysis revealed the detection of a polarisation degree P∼ 4% after 1.70 days from the trigger at 4σ confidence level, and the comparison with theoretical models suggested the presence of a homogenous jet observed inside the cone. More in general, I will discuss the role of spectro-polarimetry in GRBs afterglow analysis, also showing how it was applied to the other very few bursts analysed with this technique, i.e. GRB 020813, GRB 021004, GRB 030329, GRB 191221B.

Maria Grazia Bernardini

The SVOM mission.

SVOM (Space-based multiband astronomical Variable Objects Monitor) is a sino-french mission that is dedicated to Gamma-Ray Burst (GRB) science, expected to be launched in mid 2023. The mission includes four space-based and three ground-based instruments that, working together, will discover transients in general, and GRB in particular, providing rapid multi-wavelength follow-up to obtain a complete coverage of their emission over seven decades in energy, from the trigger up to the very late phases of the Afterglow. Thanks to its characteristics, SVOM will play a crucial role in time-domain and multi-messenger Astronomy.

Luca Izzo

The first orphan GRB detected through its associated SN emission.

In this talk I will present and discuss the case of SN 2020bvc, a broad-lined supernova showing an early optical emission excess, attributable to the cocoon emission, and delayed X-ray and radio emission originating from an off-axis jet. The analysis of the multi-wavelength data and their interpretation will be discussed, in addition to future perspectives for the detection of jet-cocoon emission at optical and radio frequencies.

Alessio Mei

GeV emission from a compact binary merger.

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 discovery of an optical-infrared kilonova (KN) points to a compact object binary merger origin. We have analysed the radio-to-GeV afterglow emission of this source. In particular, the analysis of the high energy (HE, 0.1-10 GeV) data, provided by Fermi/LAT, revealed a significant emission (> 5sigma) detected in two epochs at late times (~10^3 and ~10^4 s after the burst) with approximately constant flux (~5e10 erg/cm^2/s). The multi-wavelength afterglow emission is well modelled by synchrotron emission from electrons accelerated in the forward shock (FS). The model includes also the optical/NIR KN emission, which accounts for the excess in the r-band, and synchrotron-self-Compton, which is not dominant at these energies (< 10 GeV). Nonetheless, the LAT emission in the second epoch (~10^4 s) is in substantial excess with respect to the FS+KN best-fit model. This intrinsically faint excess (Liso~10^46 erg/s) was never observed before in neither short nor long GRB populations. We interpret this new spectral component as external Inverse Compton (EIC) emission from KN optical photons and electrons accelerated in the low-power jet. The discovery of the late-time HE excess in GRB 211211A strongly challenges our current understanding of emission processes occurring in gamma-ray burst, especially at high energies, and opens a new observational window for kilonovae, which can possibly be observed also in the ~GeV spectrum.

Marco Marongiu
INAF-Osservatorio Astronomico di Cagliari

Radio data challenge the broadband modelling of GRB160131A afterglow.

Gamma-ray burst (GRB) afterglows originate from the interaction between the relativistic ejecta and the surrounding medium. The properties of the GRB afterglows depend on several aspects, such as (1) radiation mechanisms, (2) relativistic shock micro-physics, (3) circumburst environment, and (4) the structure and geometry of the relativistic jet. While the standard afterglow model accounts for the overall spectral and temporal evolution for a number of GRBs, its validity limits emerge when the data set is particularly rich and constraining, especially in the radio domain. In this context, we analysed the afterglow of the long GRB160131A (redshift z = 0.972), for which we collected a rich, broadband, and accurate data set, spanning from radio to X-ray frequencies, and from 330 s to 160 days post-burst in time. In particular, we modelled the spectral and temporal evolution of this GRB afterglow through two approaches: (1) the adoption of empirical functions to model an optical/X-ray data set, later assessing their compatibility with the radio domain; and (2) the inclusion of the entire multi-frequency data set simultaneously through the Python package named sAGa (Software for AfterGlow Analysis), to obtain an exhaustive and self-consistent description of the micro-physics, geometry, and dynamics of the afterglow. From the deep broadband analysis of the afterglow light curves, GRB160131A outflow shows evidence of jetted emission. Moreover, we observe dust extinction in the optical spectra, and energy injection in the optical/X-ray data. Finally, radio spectra are characterised by several peaks that could be due to either interstellar scintillation (ISS) effects or a multi-component structure. The inclusion of radio data in the broadband set of GRB160131A makes a self-consistent modelling barely attainable within the standard model of GRB afterglows.

Maria Edvige Ravasio
Radboud University

New insights into the physics of GRB prompt emission from high energy observations.

Recent findings from the spectral analysis of the GRB prompt emission at both X-rays and gamma-rays provided strong observational evidences in favor of the synchrotron interpretation, finally paving the way for a solution of the GRB mystery after years of debate. However, these results imply a severe challenge for the GRB standard model, requiring a low magnetic field B~10 G and large distance R~10^16 cm from the central engine. The newly proposed proton-synchrotron scenario seems a promising solution, but the implied limited region of the parameter space hampers its capability to explain all observations. In this context, the characterization of the spectrum at high energies (MeV-GeV) can play a major role in breaking the degeneracies and distinguishing the GRB emission models. By possibly holding the signature of pair-production opacity, which is independent from the radiative process, the high energy spectrum can provide precise measurements of the bulk Lorentz factor of the jet, a key parameter of GRB physics. Moreover, the extension of the accessible energy range helps in unveiling the physics of the poorly known acceleration process, thanks to the constraints on the particles' energy distribution derived from the high-energy spectral powerlaw. Finally, we can exploit the full potential of the high energy observations by combining them with the information derived from the afterglow lightcurves, allowing us to obtain the distance R from the central engine, a fundamental but still unknow physical parameter of the prompt emission, finally shedding a light on the mystery of GRBs (Ravasio et al. 2022, in prep).

Giulia Stratta

The Transient High-Energy Sky and Early Universe Surveyor (THESEUS).

The Transient High-Energy Sky and Early Universe Surveyor (THESEUS) is a space mission concept selected by ESA for a Phase A study (2018-2021) as candidate M5 mission, and currently being reproposed for the recently opened ESA/M7 opportunity for a launch in 2037. THESEUS aims at exploiting Gamma-Ray Bursts for investigating the early Universe and at providing a substantial advancement of multi-messenger and time-domain astrophysics. Through an unprecedented combination of X-/gamma-rays monitors, an on-board IR telescope and automated fast slewing capabilities, THESEUS will be a wonderful machine for the detection, characterization and redshift measurement of any kind of GRBs and many classes of X-ray transients. In addition to the full exploitation of high-redshift GRBs for cosmology (pop-III stars, cosmic re-ionization, SFR and metallicity evolution up to the "cosmic dawn"), THESEUS will allow the identification and study of the electromagnetic counterparts to sources of gravitational waves which will be routinely detected in the second half of the '30s by next generation facilities like aLIGO/aVirgo, LISA, KAGRA, and Einstein Telescope (ET), as well as of most classes of transient sources, thus providing an ideal synergy with the large e.m. facilities of the near future like LSST, ELT, TMT, SKA, CTA, ATHENA.

Matteo Ferro
INAF – Osservatorio Astronomico di Brera

Search for afterglow and kilonova emission in short GRBs.

The study of short GRBs (SGRBs) in the local Universe is of particular interest for the association of these elusive events with GWs and kilonovae (KNe). I will present the results of deep follow-up observations of two, possibly nearby, recent SGRBs. GRB 211106A was firstly associated to a galaxy at z=0.097 while GRB 211227A (a SGRB with extended emission) is possibly linked to a host at z=0.228. For the two bursts we carried out observations in several optical and NIR bands with different ESO-VLT intruments (FORS2, HAWK-I, MUSE and X-SHOOTER) in multiple epochs, enabling us to derive tight limits and constraints on the associated afterglow and KNe emission. I will discuss the implication of these results in the broader context of SGRBs properties.

Davide Miceli
Università e INFN Padova

Very high energy emission from gamma-ray bursts with the MAGIC telescopes.

Since almost 20 years the MAGIC telescopes perform observations of gamma-ray bursts (GRBs). The follow-up strategy and the specific design of these telescopes, namely a fast slewing system (7deg/s), a low energy threshold (around 50 GeV) and the possibility of performing observations in imperfect conditions, make them the most suitable instrument for the observation of GRBs in the very high energy domain. The effort in the refinement of such strategy finally paid off in January 2019 with the first TeV detection of a GRB, namely GRB190114C. Such discovery shed light on the physical processes involved and on several unknown aspects of GRB afterglow physics. This opened a new era for GRB studies with MAGIC, including the detection of GRB201216C and the studies performed for the hint of detections from GRB160821B and GRB201015A. In this contribution I will present the main results achieved and the future challenges that the MAGIC telescopes can address in the GRB field.

Graziella Pizzichini

GRBs at high redshift.

I shall report on an ongoing search for particular properties of GRBs at high redshift

Anna Elisa Camisasca
Università di Ferrara

Optimising the observation strategy of optical counterparts to short GRBs with robotic Liverpool Telescope.

In collaboration with the Astrophysics Research Institute (Liverpool John Moores University) GRB team and Dr. Mattia Bulla (Stockholm University), I studied how to optimise the observation strategy (sequence of filters and exposure times) of robotic observations of kilonovae with the MOPTOP ( Multicolour OPTimised Optical Polarimeter) curretly deployed at the 2-m Liverpool Telescope. The ultimate goal is to constrain the properties of the kilonovae associated with short GRBs. To this aim, I made use of the synthetic light curves of the kilonovae for different viewing angles, distances, and kilonovae models.

Marco Citossi

Nano-Spazio INAF FVG outreach program.

Nano-Spazio INAF FVG is an outreach program carried out by INAF-OATs in close collaboration with the "Istituto Malignani" high school of Udine. INAF-OATs participates to the so-called 'Alternanza Scuola-Lavoro' (i.e. 'school-work synergy') outreach project promoted by the Italian government, with the primary aim of bringing students closer to space-related activities before choosing their university studies. The outreach program is split into three parts: one with frontal lessons, which present and discuss relevant topic of astrophysics, and one practical, consisting of hands-on activities aimed to replicate scientific analysis of real space data. The last part of the program includes the assembly of nano-satellite payload to launch in a stratospheric balloon, developed in collaboration with the HERMES-SP project. Students (in number of 25, coming from different courses of study) and their teachers are involved in the design, construction, test and operation of detectors for the measurement of several properties of the cosmic ray flux. This turns out to be an excellent educational laboratory to introduce non-experts, especially students, to the study of physics and fundamental natural phenomena. On the other hand, cosmic radiation is easily intercepted and can easily "be made visible" through simple particle detector telescopes as ArduSiPM detectors. The study of cosmic radiation is also closely linked to the other major themes of modern astrophysics, from dark matter to gravitational waves and gamma ray bursts and much more. Talking about cosmic rays means therefore talking about the exploration of the Universe in all its forms. For this reason, it was decided to use instrumentation and experimental data to create an online pathway to allow the acquisition of notions useful to learn what cosmic rays, extensive air showers (EAS), muons and other quantities useful to understand cosmic radiation are, as well as understand the functioning of the instruments to detect them, especially to perform measurements of atmospheric muons under different conditions. Finally, the results of a set of measurements, made with the ArduSiPM detectors under different conditions, has to be described (i.e. measurement of the cosmic muon rate, measurement of muon angular distribution and measurement of muon intensity as a function of the zenith angle). The impact of this project on the students' attitude has been then evaluated by means of questionnaires specifically designed to gather information on the students' educational background, the level of engagement triggered by the proposed activities, their relevance to school-based activities, and the perceived ease of understanding of the covered topics. The analysis of the answers clearly shows that students greatly appreciated this outreach project, supporting its possible expansion and development, even articulated in a more complex pedagogical plan,


Any question? please feel free to contact us at grbv@inaf.it


IFPU (Institute for Fundamental Physics of the Universe)

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