Third Gravi-Gamma Workshop: The multimessenger view of the black hole life cycle


Multi-messenger astrophysics has become a distinct discipline with the great potential to reveal new clues on the properties and processes of the physical universe. Gravitational waves provide a radical new way to study the darkest depths of the cosmos, black holes. With the first three observing runs performed by LIGO, Virgo and KAGRA we are now capable of performing population studies revealing the first identification of intermediate-mass black holes. These sources are of particular interest since they may hold the key to one of the big puzzles in astrophysics and cosmology: the origin and evolution of supermassive black holes. As extraordinary as the past few years of discoveries have been, they have only revealed the tip of the iceberg and in order to gather a complete understanding of the life cyle of these enigmatic objects we need to rely on the multi-messenger approach and combine the observations from Pulsar Timing Arrays, neutrinos, and electromagnetic observatories. The goal of the third edition of the Gravi-Gamma workshop is to bring together experts in the fields of observational and theoretical multi-messenger science to explore the black hole life cycle.

This workshop is funded by a grant from the Italian Ministry of Foreign Affairs and International Cooperation. This event is also supported by AHEAD2020, funded by the Horizon 2020 Framework Programme of the European Union, GA No. 871158

  • Alberto Bonollo
  • Alberto Mangiagli
  • Alberto Sesana
  • Aldo Morselli
  • Alessandra Berretta
  • Alessio Fiori
  • Andrea Melandri
  • Antonio Marinelli
  • Barbara Patricelli
  • Claudio Gasbarra
  • Daniele Belardinelli
  • Federica Giacchino
  • Federico De Santi
  • Giacomo Principe
  • Giancarlo Cella
  • Giuseppe Greco
  • Gor Oganesyan
  • Irene Di Palma
  • Irina Dvorkin
  • Koutarou Kyutoku
  • Luca Baldini
  • Maria Lisa Brozzetti
  • Marion Pillas
  • Marta Di Corrado
  • Massimiliano Razzano
  • Matthew Kerr
  • Melissa Pesce-Rollins
  • Michał Bejger
  • Michele Punturo
  • Nunziato Sorrentino
  • Paolo Cristarella Orestano
  • Pasquale Lubrano
  • Paul Scholz
  • Ryan Fisher
  • Samuele Ronchini
  • Sara Buson
  • Sara Cutini
  • Stefano Ciprini
  • Stefano Germani
  • Stefano Rinaldi
  • Tobia Matcovich
  • Vasco Gennari
  • Viviana Fafone
    • 9:00 AM
    • Stellar and Intermediate black holes
      Convener: Melissa Pesce-Rollins (Istituto Nazionale di Fisica Nucleare)
      • 1
        Past, present and future of gravitational-wave astronomy

        Beginning with GW150914, the LIGO-Virgo-Kagra collaboration observed 90 compact binary coalescences, 11 during the first two observing runs (O1 and O2) and the remaining 79 during the third, O3.

        The implications of these observations in physics and astronomy are countless: from tests of general relativity to insights into binary formation and evolution, from multimessenger observations to cosmological measurements. With the fourth observing run (O4) scheduled for next year, more gravitational-wave events are expected to expand the catalog, bringing with them new insights on our Universe.

        In this talk, I will describe selected recent results obtained by the LIGO-Virgo-Kagra collaboration after the end of O3 as well as some of the prospects for O4, both from the point of view of detector sensitivities and expected observations.

        Speaker: Stefano Rinaldi (Istituto Nazionale di Fisica Nucleare)
      • 2
        Probing modified gravity theories and cosmology using gravitational-waves and associated electromagnetic counterparts

        The standard cosmological model is one of the main predictions of General Relativity (GR). Although very successful, the standard cosmological model still suffers some theoretical and observational issues such as the nature of Dark Energy and the H0-tension. Modifications of GR at cosmological scales are a possible avenue to solve these problems. In this talk, I will discuss how gravitational-wave bright standard sirens can be used to probe GR on cosmological scales. In particular, I will focus on theories that introduce an additional friction term and dispersion relation to GW propagation. I will show that combining 100 binary neutron stars detections associated with a short Gamma-ray burst and host galaxy identification, will suffice to measure the Hubble constant, the GW friction GW dispersion relation (graviton mass) with 2%, 15%, and 2% accuracy, respectively. Finally, I will apply the same study to GW170817, and demonstrate that for all of the GW dispersions relations we consider, including massive gravity, the GW must be emitted ∼1.74 s before the gamma-ray burst. Furthermore, at the GW merger peak frequency, we show that the fractional difference between the GW group velocity and c is ≲10^-17.

        Speaker: Simone Mastrogiovanni
      • 3
        Constraining the black hole population with Gravitational Waves

        Starting with the first detection of gravitational waves (GWs) in September 2015, a total of 90 compact binary coalescences (CBCs) have been detected so far by Advanced LIGO and Advanced Virgo, including mergers between BHs, NSs and mixed NS-BHs. These GW observations allowed us to infer some properties of the NS and BH populations, such as the mass and spin distributions and the merger rates: these are key ingredients to better understand the physics of binary mergers and the origin of these systems. In the next years we expect to have more GW detections of CBCs, thanks to the increasing sensitivity of GW detectors, and future GW observations will be crucial to get more insights on the population of binary compact objects.
        In this talk I will review some recent results and summarize the astrophysical interpretation of the population properties inferred through GW observations, with focus on the BH population; I will also discuss what we expect to learn from future GW discoveries.

        Speaker: Barbara Patricelli (Istituto Nazionale di Fisica Nucleare)
    • 11:30 AM
      Coffee break
    • Stellar and Intermediate black holes
      Convener: Melissa Pesce-Rollins (Istituto Nazionale di Fisica Nucleare)
      • 4
        Future GW astronomy in Europe: Einstein Telescope.
        Speaker: Dr Michele Punturo (INFN Perugia)
      • 5
        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 explore the perspectives of ET operating as single observatory and in a network of next generation gravitational-wave observatories (such as Cosmic Explorer), in synergy with future gamma-ray and X-ray satellites. 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 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 emphasise the crucial role of future wide field X-ray missions also for the detection of the fainter emission outside the jet core, which will allow us to probe the yet unexplored population of low-luminosity short GRBs in the nearby Universe, as well as to unveil the nature of the jet structure and the connections with the progenitor properties.

        Speaker: Dr Samuele Ronchini (Istituto Nazionale di Fisica Nucleare)
    • 1:00 PM
    • Stellar and Intermediate black holes
      Convener: Massimiliano Razzano (Università di Pisa)
      • 6
        Coalescence of black hole-neutron star binaries

        Black hole-neutron star binaries are among the least understood population of compact binary coalescences. LIGO-Virgo O3 reported detection of a black hole-neutron star binary, GW200115, along with some candidates. Future observations will definitely deliver a lot of black hole-neutron star binaries, some of which might be accompanied by electromagnetic counterparts. In this talk, I will review the coalescence process and observable signatures of black hole-neutron star binaries, addressing the difference with other types of compact binary coalescences.

        Speaker: Koutarou Kyutoku (Kyoto University)
      • 7
        Continuous GWs from known and unknown sources: O3 observations and beyond

        The binary inspirals are only a beginning of a list of potentially
        detectable signals. Still undiscovered types of GW radiation include long-
        lasting, almost-monochromatic continuous gravitational waves (CWs), whose amplitudes and frequencies evolve much slower, compared to those of transient GW sources. Promising sources of CW are rotating, non-axisymmetric NS, emitting GWs at a frequency related to their spin frequency. Deviation from the symmetry (low-multipole NS deformation, informally called a ''mountain'') may be caused by a number of astrophysically-interesting processes: fluid instabilities, such as the r-modes, or by elastic, thermal or magnetic stresses in the crust and/or core of NS, and may be acquired at various stages of stars’ isolated evolution, or during an interaction with a stellar companion in a binary system. In addition to neutron stars primordial black holes in binary systems and other exotic dark matter candidates may be sources of CWs. In this talk I will summarize results from the LIGO-Virgo-KAGRA O3 run, and present prospects for the incoming O4 run.

        Speaker: Bejger Michal (APC and CAMK)
      • 8
        What can we learn about stellar- and intermediate-mass black holes from multi-messenger observations?

        Our understanding of the formation paths of stellar-mass and intermediate-mass black holes has drastically changed in recent years. In particular, the masses of black hole binaries observed in gravitational waves are challenging existing theories. In this talk I will discuss the main open questions and the prospects of answering them with multi-messenger observations.

        Speaker: Irina Dvorkin (Institut d'Astrophysique de Paris, Sorbonne Université)
    • 4:30 PM
      Coffee break
    • Stellar and Intermediate black holes: Contributed Talks
      Convener: Massimiliano Razzano (Università di Pisa)
      • 9
        Deep learning approach to detect gravitational waves from binary close encounters

        Gravitational wave (GW) emission from close encounters (CEs) between neutron stars (NSs) and/or
        black holes (BHs) are recently being considered as new potential astrophysical sources for ground-
        based detectors. CEs are mostly part of three-body systems, constrained by a dense stellar environ-
        ment and configured in eccentric inspirals, characterized by repeated dynamical captures. These
        are predicted to occur with both GW and gamma-ray emission, thus resulting interesting for mul-
        timessenger astronomy. Their GW waveform is hard to model with respect to quasi-circular iso-
        lated inspiraling binary systems, already observed by the LIGO/Virgo collaboration. Unmodeled
        burst search could be a viable method for detecting such systems in Advanced LIGO and Virgo
        data. We propose a deep learning-based approach for CE detection, based on convolutional neural
        networks capable of detecting transient signals associated to CEs and distinguishing them from
        transient noises that can mimic GW signals (glitches). The training of the algorithm is based on
        simulated timeseries of Virgo data. We present preliminary results on of this approach, using a
        one-dimension convolutional neural network architecture, as a first step toward the application to
        real data.

        Speaker: Sorrentino Nunziato (University of Pisa and INFN)
      • 10
        A Bayesian approach to pulsar timing and its applications to multi-messenger astrophysics

        The Fermi Large Area Telescope is enabling a revolution in pulsar physics, having detected almost
        300 gamma-ray pulsars. Many Fermi pulsars show glitches, and one of them, the radio-quiet PSR
        J2021+4026, is variable on a time scale of a few years. Pulsar glitches are considered as possible
        sources of detectable gravitational waves and probes of neutron star interiors. Therefore, multi-
        messenger astrophysics could benefit of a monitoring infrastructure and a systematic study of
        glitches in Fermi-LAT pulsars. We will report on GLIMPSE, a Python toolkit for the analysis of
        gamma-ray pulsar glitches. Our analysis pipeline consists in a Bayesian search for a periodic signal
        in the presence of a glitch, and it has the goal of estimating the parameters of a pulsar timing model.
        The product of this pipeline will be a table containing parameters for all detected events, which will
        be periodically updated. For each glitch we will include the amplitude of the expected gravitational
        wave signal, which will be inferred starting from models for neutron star interiors. Results will be
        available on a web application and could be used to plan targeted searches for gravitational-wave
        transients. Here we will present some preliminary results obtained using this infrastructure, and
        we will discuss its future applications to multi-messenger astrophysics.

        Speaker: Alessio Fiori (INFN )
      • 11
        Observing the Ringodwn: On the Detectability of Higher Modes

        The last phase of black hole binary coalescences is known as the ringdown, in which the newly-
        formed black hole relaxes to its stationary state by emitting gravitational waves. Ringdown studies
        are crucial, providing a unique way of studying gravity in extreme curvature regime and better
        understanding the nature of black holes. The linear theory of black hole perturbations predicts
        that the ringdown is made by a sum of different modes of vibration, which are exponentially-
        damped harmonics oscillations projected onto spherical harmonics. The excitation of the different
        modes depends on the specific process that perturbs the black hole, and for quasi-circular binary
        coalescences the fundamental mode dominates the ringdown emission. Besides, asymmetries in
        the system and its inclination with respect to the observer can excite higher subdominant modes
        of vibration. The measurement of the frequencies and damping times of these higher modes allows
        to test general relativity by comparing the predicted values against the observations.
        We describe the first time domain analysis with an effective one-body ringdown model on the third
        catalog of gravitational waves events GWTC-3, both for parameters estimation and to assess the
        detectability of higher modes in the events. This work sets the bases towards the positive identi-
        fication and characterisation of higher modes in the ringdown signals with future, more sensitive
        gravitational wave detectors, and opens the concrete possibility of conducting multimodal tests of
        general relativity in the strong field regime.

        Speaker: Vasco Gennari (INFN Pisa)
    • Stellar and Intermediate black holes
      Convener: Stefano Germani (Istituto Nazionale di Fisica Nucleare)
      • 12
        Searching for Gravitational-Wave / Gamma-Ray-Burst associations in LIGO/Virgo and Fermi-GBM data

        The GW170817 event provided the first observation of gravitational waves from a neutron star merger with associated transient counterparts across the entire electromagnetic spectrum. This discovery demonstrated the long-hypothesized association between short gamma-ray bursts and neutron star mergers. More joint detections are needed to explore the relation between the parameters inferred from the gravitational wave and the properties of the gamma-ray signal, potentially ruling out some of the existing models of the physical processes responsible for these events. Groups in LIGO/Virgo/KAGRA, Fermi and Swift collaborations have developed many searches for joint gravitational-waves/gamma-ray-bursts detections. We will start with an overview of all these searches, and then present a deeper method aimed at detecting weak gravitational-waves transients associated with weak gamma-ray-bursts. Contrary to other searches, this search for coincidences between the gravitational—waves and gamma-ray-bursts triggers does not require a confident detection in one of the two channels. The candidate coincidences are ranked according to a statistic that combines each candidate's strength in gravitational-waves and gamma data, the time proximity of the transients in gravitational-waves and gamma data, and the overlap of the gravitational-waves and Fermi/GBM sky localizations. The ranking is then converted to a false-alarm by using time shifts between the gravitational-waves and Fermi/GBM triggers.
        We will present the results of this deep subthreshold joint analysis applied on triggers from the second Gravitational-Waves Observing Run, which allowed us to check the validity of our method against GW170817+GRB170817A.
        We will also discuss the different tunings we tested to increase the significance of this joint detection.

        Speaker: Marion Pillas (IJCLab, Université Paris Saclay)
      • 13
        Hunting the gamma-ray emission from Fast Radio Burst with Fermi-LAT

        Fast radio bursts (FRBs) are one of the most exciting new mysteries of astrophysics. Their origin is still unknown, but recent observations seem to link them to soft gamma repeaters and, in particular, to magnetar giant flares (MGFs). The recent detection of a MGF at GeV energies by the Fermi Large Area Telescope (LAT) motivated the search for GeV counterparts to the >1000 currently known FRBs. To date, none of these has a known gamma-ray counterpart.
        Taking advantage of more than 13 years of Fermi-LAT data, we perform a search for gamma-ray emission from almost all the reported repeating and non-repeating FRBs. We analyze on different time scales the Fermi-LAT data for each individual source separately and perform a cumulative analysis on the repeating ones. In addition, we perform the first stacking analysis at GeV energies of this class of sources in order to constrain the gamma-ray properties of the FRBs. The stacking analysis is a powerful method that allows for a possible detection from below-threshold FRBs providing important information on these objects. In this talk we present the results of our study and we discuss their implications for the predictions of gamma-ray emission from this class of sources.

        Speaker: Giacomo Principe (Istituto Nazionale di Fisica Nucleare)
      • 14
        Comprehension of jet physics from the analysis of Swift Gamma-Ray Bursts

        The discovery of a short Gamma-Ray Burst, GRB170817A, in association with a Gravitational
        Wave and a bright kilonova started a new era in the high energy astrophysics. The observation
        of GRB170817A and more recently, GRB200826A and GRB211211A, a short and a long burst re-
        spectively with a possible kilonova, have reinforced the need for new ways of classification. For
        this reason, a procedure that uses a machine learning technique searching for similarities in the
        light curves is applied to Swift-BAT prompt emission data. Two distinct groups could be identified,
        although still correlated with standard T90 duration. Since a jet viewed off-axis could explain the
        emission from GRB170817A, the modelling of this kind of sources is of great importance. A pub-
        lic code called JetFit, based on the “boosted fireball” model, is applied to fit Swift-XRT afterglow
        light curves of short and long Gamma-Ray Bursts, with known redshift, from 2005 to 2021. JetFit
        does not model the flaring activity. For this reason, a new procedure to remove the flaring phases
        has been developed. The distributions of the best-fit parameters, grouped according to the classi-
        fication given by the machine learning algorithm, describe the physics of our sample. The mean
        values of the JetFit parameters can be used to compute the Synchrotron part of a typical Gamma-
        Ray Bursts afterglow emission model. Given the synchrotron mechanism, we obtain a prediction
        on the Synchrotron Self-Compton high-energy component by building a general model based on
        physical parameters of the afterglow.

        Speaker: Alessandra Berretta (INFN)
    • 10:30 AM
      Coffee break
    • Stellar and Intermediate black holes
      Convener: Stefano Germani (Istituto Nazionale di Fisica Nucleare)
      • 15
        A machine learning approach to discover core collapse supernovae

        The recent discovery of gravitational waves and high-energy cosmic neutrinos, marked the beginning of a new era of the multimessenger astronomy. These new messengers, along with electromagnetic radiation and cosmic rays, give new insights into the most extreme energetic cosmic events. The detection of gravitational waves from core-collapse supernova explosions is a challenging task, yet to be achieved, in which it is key the connection between multiple messengers, including neutrinos and electromagnetic signals. In this talk, I present a method for detecting these kind of signals based on machine learning techniques. To test its robustness signals were injected in the real noise data taken by the Advanced LIGO-Virgo network during the second observing run, O2, it would have been possible to reach the event distance values up to 14 kpc.

        Speaker: Irene Di Palma (Istituto Nazionale di Fisica Nucleare)
      • 16
        Neutrino astronomy in the era of the Global Neutrino Network

        After several decades from their conception kilometric volume neutrino telescopes put the basis for a very-high-energy neutrino astronomy. The samples of astrophysical events detected by the IceCube collaboration show spectral energy distributions compatible with a multicomponent astrophysical origin. While the low energy part of this measured flux can be accounted by the “reservoirs” emission the high energy one is naturally explained by extragalactic accelerators. Track-like event samples obtained from long observational time of IceCube and Antares telescopes did not showed a clear signature of know galactic or extragalactic point-like objects. On the other hand multi-messenger follow-ups of peculiar astrophysical events, like TXS0506+056 already indicated enthusiastic perspectives. A different case is represented by the diffuse neutrino fluxes analysis where we already got important hints about their origin.
        The incoming Global Neutrino Network based on IceCube/IceCube-Gen2, KM3NeT, Baikal-GWD and P-ONE will be crucial to constrain the different astrophysical components as well as to optimize the follow-up strategy for electromagnetic and gravitational wave transient events. In this presentation we review the status of long observational periods with related astrophysical evidences as well as the high-energy neutrino follow-up programs.

        Speaker: Antonio Marinelli (Istituto Nazionale di Fisica Nucleare)
      • 17
        Gravitational-wave sky localizations: online calculator and interactive viewer of credible areas

        We will show a new web tool dedicated to multi-messenger astrophysics both for archival research
        and real-time analysis. The web tool is based on the Virtual Observatory (VO) standards permitting
        to manage sky localizations in HEALPix (Hierarchical Equal Area isoLatitude Pixelation) format
        from various missions.
        The application has been developed in accordance with the FAIR (Findability, Accessibility, Inter-
        operability, and Reusability) principles, allowing the efficient exchange of essential information
        between various partners in multi-messenger campaigns.

        Speaker: Giuseppe Greco (INFN)
      • 18
        Estimation of detection probabilities of Gamma-Ray Burst and Gravitational Waves multimessenger events produced by distruptive binary mergers

        In this presentation I will analyse the coalescence events of compact binary objects, in particular
        the mergers of the black hole-neutron star type, with multimessenger approach. Studying the
        short Gamma-Ray Burst electromagnetic counterpart I used a recent model to make predictions
        about both the synchrotron and synchrotron self-Compton afterglow emission and I will discuss
        its possibile detection in the high energy band using the Fermi-LAT and CTA instruments.

        Speaker: Matcovich Tobia (INFN Perugia)
      • 19
        Evaluation of catalogues’ completeness by extending the Virtual Observatory framework to estimate the H0 Hubble constant with dark standard sirens

        About one hundred years ago, Edwin Powell Hubble made the first measure of the rate of expansion
        of the Universe but still today different techniques of investigation lead to different results. This
        dilemma is called Hubble tension and gravitational waves play a key role in its resolution.
        The talk focuses on BBH mergers, called dark standard sirens in cosmological applications, and on
        the possible use of statistical Bayesian methods.
        The study of the rate expansion of the Universe with BBH involves also the use of galaxy catalogues,
        as GLADE (v 2.4) which turns out to be an excellent complete catalogue in B-band.
        We set out to define a parameter that can estimate the completeness in the 90% credible volume of
        a GW event within the framework of the Virtual Observatory.
        The completeness coefficient C has been derived for each gravitational event detected in the first
        three observational runs of LVK (O1, O2 and O3a).

        Speaker: Maria Lisa Brozzetti (INFN)
    • 1:00 PM
    • Stellar and Intermediate black holes
      Convener: Giuseppe Greco (INFN)
      • 20
        Unusual GRB afterglow features

        The standard gamma-ray burst (GRB) afterglow model is based on the deceleration of an ultra-relativistic jet in the circumburst medium. It predicts a simple power-law decline of multi-wavelength and long-lived emission following the prompt emission. The X-ray Telescope onboard the Neil Gehrels Swift Observatory has discovered several features in the afterglow light curves which deviate from the standard approach. These features in the X-ray afterglow emission include the initial steep decline, long-lasting flat segments (plateau) and bright X-ray flares. In the newly established multi-messenger astronomy with gravitational waves, it is extremely important to understand the observations from the geometry of the jet. This will allow us to model the most common multi-messenger scenario, i.e. what we will observe off-axis. I will discuss the zoo of models for the X-ray afterglow emission and their predictions for the off-axis observers. I will also discuss newly discovered GeV emission in association with the compact binary merger (GRB 211211A), which is also in excess with the standard afterglow emission model.

        Speaker: Gor Oganesyan (Gran Sasso Science Institute)
      • 21
        A fast radio burst from a Galactic magnetar

        Fast radio bursts (FRBs) are bright millisecond-duration bursts of radio waves coming from far outside the Galaxy whose nature is an ongoing mystery in astrophysics. A leading model for FRBs is that they are extragalactic magnetars, young neutron stars whose emission is powered by their extremely strong magnetic fields. However, a challenge to these models was that FRBs must have radio luminosities many orders of magnitude larger than those seen from known Galactic magnetars. On 2020 April 28, the Canadian Hydrogen Intensity Mapping Experiment (CHIME) FRB project discovered a bright radio burst from Galactic magnetar SGR 1935+2154 during a known state of X-ray outburst. The radio burst energy of the detected burst was three orders of magnitude higher than any radio emission previously seen from a Galactic magnetar and it overlaps with the faintest known extragalactic FRBs. This discovery strongly signals that at least some FRBs originate from magnetars, although the fraction is unlikely to be unity and may even be small. In this talk I will present the CHIME/FRB discovery of the radio burst, put it in context with the wider evidence for and against FRBs as magnetars, and discuss the implications of this landmark result.

        Speaker: Paul Scholz
      • 22
        High-energy emission from a magnetar giant flare in the Sculptor galaxy

        Magnetars are neutron stars with the strongest magnetic fields known in the Universe, with an intensity up to a thousand times higher than typical neutron stars. Rarely, magnetars can produce enormous eruptions, called Magnetar Giant Flares (MGF), consisting of short-duration bursts of hard X-rays and soft gamma rays. On April 15, 2020, a short bright burst of MeV gamma rays triggered the Gamma-Ray Burst Monitor (GBM) aboard the Fermi spacecraft, called GRB 200415A and localized by the InterPlanetary Network (IPN) inside the disk of the nearby Sculptor galaxy. Starting 19 seconds later, and for nearly 300 seconds, the Large Area Telescope (LAT) detected GeV photons in spatial coincidence with the signal at lower energies. In this talk we present the recently published results of the GBM and LAT analysis on GRB 200415A. Detailed analyses show that the sub-MeV emission has peculiar properties typically observed in flares from nearby magnetars. The GeV detection, consistent with the IPN localization and spatially associated with the Sculptor galaxy, represents the first detection of the high-energy emission from a MGF and likely arises from an energetic, ultra-relativistic MGF outflow, as it collides with an external bow-shock shell. This discovery demonstrates that these events could constitute their own class of GRBs and motivated us to perform a combined GBM-LAT search over 14 years of Fermi data to discover additional yet unidentified MGFs.

        Speaker: Niccolò Di Lalla (Stanford University)
    • 4:30 PM
      Coffee break
    • Stellar and Intermediate black holes
      Convener: Giuseppe Greco (INFN)
      • 23
        Search for gravitational waves associated with Fast Radio Bursts Detected by CHIME/FRB During the LIGO-Virgo Observing Run O3a

        We present the search for gravitational waves associated with fast radio bursts detected by the CHIME/FRB experiment during the LIGO-Virgo Observing Run O3a, from 1 April 2019 15:00 UTC - 1 October 2019 15:00 UTC. Targeted searches for GW events using both modelled compact-binary-coalescence and unmodelled searches were used. We will present results for the exclusion distances generated by the searches in comparison to the fast radio burst events' luminosity distances as well as upper limits on the total amount of energy released in gravitational waves for these events.

        Speaker: Ryan Fisher (Christopher Newport University)
      • 24
        Stochastic Gravitational-Wave Backgrounds: Current Detection Efforts and Future Prospects With Ground-based Interferometers

        The collection of individually resolvable gravitational wave (GW) events makes up a tiny fraction
        of all GW signals in our Universe, while most lie below the confusion limit of our observatories
        and thus remain undetected. Like voices in a crowded room, the collection of unresolved signals
        gives rise to a background which is well–described via stochastic variables, and hence referred
        to as the stochastic GW background (SGWB). In a recent review paper [arXiv:2202.00178], we
        outline what possible GW sources can contribute to such a background, and give an overview of
        stochastic detection methods with different GW experiments. In this talk, I will focus on detection
        methods with the current second generation (2G) interferometer network, laying out a roadmap to
        detection. In the process, I will characterize the SGWB we expect to measure with the 2G network,
        and highlight the challenges we face when trying to measure this elusive signal. Finally, I will
        briefly outline future detection prospects with third generation (3G) interferometers and review
        proposed data analysis techniques tailored to this class of detectors.

        Speaker: Arianna Renzini (Caltech)
    • 8:00 PM
      Social dinner Ristorante Etruria

      Ristorante Etruria

      Piazza dei Priori, 6/8 56048 – Volterra
    • Supermassive black holes
      Convener: Sara Cutini (INFN)
      • 25
        Multimessenger opportunities with massive black hole binaries

        Massive black hole binaries (MBHBs) are expected to be the loudest gravitational wave (GW) sources in the milli-Hz window which will be probed by the future Laser Interferometer Space Antenna. MBHs are also known to radiate at large luminosities, opening the possibility of future multimessenger observations of MBHBs. I will describe the dynamics of MBHBs, their expected GW and electromagnetic signals and prospects for multimessenger astronomy in the next decade.

        Speaker: Alberto Sesana (Albert Einstein Institute, Golm)
      • 26
        Searching for Gravitational Waves with Gamma Rays

        Pulsar timing arrays (PTAs) are long-term monitoring campaigns of many millisecond pulsars (MSPs). Their key science goal is the detection and characterization of the few-nHz gravitational wave background (GWB) expected primarily from the mergers of supermassive black holes. These waves are random (stochastic), but the shared vantage point of the earth introduces hallmark correlations in the data which encode the strength and nature of the GW sources. The Fermi Large Area Telescope has detected more than 100 MSPs, and with its accurate and precise timestamping, it is a gamma-ray PTA. Sensitivity to the GWB increases dramatically with longer data sets, and we recently derived an upper limit on the GWB which is competitive with radio observing campaigns but free from many confounding effects, like propagation through the ionized interstellar medium. Here, we summarize these original results, give an update based on proposed improvements to the measurement precision, and discuss prospects for the eventual detection and characterization of the GWB.

        Speaker: Matthew Kerr (Naval Research Laboratory)
    • 10:30 AM
      Coffee break
    • Supermassive black holes
      Convener: Sara Cutini (INFN)
      • 27
        Unveiling early black hole growth with multi-frequency gravitational wave observations

        In $\sim 2034$ LISA will be able to detect the gravitational waves (GWs) from the coalescence of massive black hole binaries (MBHBs) in between $[10^5,10^7] \, \rm M_{\odot}$ solar mass up to $z\sim 10$. If the merger happens in a wet environment, copious amounts of radiation across the entire electromagnetic (EM) spectrum is expected to be produced by the accretion of the gas onto the binary.
        If LISA locates the MBHB merger within an error box of sub-squared degree accuracy, EM telescopes can be pointed to identify the host galaxy and detect the EM counterpart to the GW signal, paving the way to test the nature of gas in a rapidly changing space-time and to perform cosmology and General Relativity experiments.
        In this talk I will discuss the possibilities to observe jointly the GW and EM signal and recent results on the synergies between LISA and future EM facilities such as LSST, SKA, Athena.

        Speaker: Alberto Mangiagli (APC)
      • 28
        Neutrinos from stellar tidal disruption events

        While most stars orbit about the center of their host galaxy for their entire lifetime, a few of them are less fortunate. Two-body interactions can scatter an unlucky star towards the supermassive black hole at the center of the galaxy. This star will suffer a tidal disruption and the resulting stellar debris gets accreted into the black hole. These stellar tidal disruptions events are rare and result in a spectacular flare of electromagnetic radiation. Visible from radio to X-ray wavelengths, tidal disruption flares are a unique probe to study massive black holes. Over the last decade, astronomers have gotten increasingly adept at finding these events. The advent of optical transient surveys has accelerated this effort, resulting in a large number of (often unexpected) discoveries. In this talk I will review this progress, in particular the recent discovery of neutrino counterparts to tidal disruption events.

        Speaker: Dr Sjoert Van Velzen (Leiden University)
      • 29
        Beginning a journey across the Universe: the discovery of extragalactic neutrino factories

        Neutrinos are the most elusive particles in the Universe, capable of travelling nearly unimpeded across it. Despite the vast amount of data collected, a long standing and unsolved issue is still the association of high-energy neutrinos with the astrophysical sources that originate them. Amongst the candidate sources of neutrinos there are blazars, a class of extragalactic sources powered by supermassive black holes that feed highly relativistic jets, pointed towards the Earth. Previous studies appear controversial, with several efforts claiming a tentative link between high-energy neutrino events and individual blazars, and others putting into question such relation. In this work we show that blazars are unambiguously associated with high-energy astrophysical neutrinos at unprecedented level of confidence, i.e. chance probability of 2 × 10^{−6}. This statistical analysis provides the observational evidence that blazars are astrophysical neutrino factories and hence, extragalactic cosmic-ray accelerators.

        Speaker: Sara Buson (Univ. of Wuerzburg)
    • 1:00 PM
    • Electromagnetic detectors and future prospects for multimessenger science and contributed talks
      Convener: Giancarlo Cella (Istituto Nazionale di Fisica Nucleare)
      • 30
        New Robotic Telescope in the context of EM Detectors and future prospects for Multimessenger science

        The discovery of gravitational waves (GWs) from the coalescence of compact objects is one of the most exciting scientific discoveries of the last decade, and started a “golden age” for the multi-messenger astronomy. Merging of either black hole-neutron star or two neutron stars are among the most promising GW sources able to generate electromagnetic counterparts, but also core-collapsing massive stars and isolated neutron stars could be detected in the near future. Several electromagnetic counterparts, such as gamma-ray bursts and their afterglows, kilonovae, millisecond pulsars, soft gamma repeaters and core-collapse supernovae, are expected to be associated with these sources. Comprehensive follow-up observational campaigns of GW signals will help to answer to some fundamental questions in astrophysics and physics in general, leading to a more complete understanding of these events. I will review the current status of the observations of GW sources and their EM counterparts and the future perspectives for joint multi-messenger observational campaigns with current and future instrumentation.

        Speaker: Andrea Melandri (INAF - OAB)
      • 31
        Very High Energy facilities in the context of Electromagnetic Detectors and future prospects for Multimessenger science

        The recent detection Gamma Ray Burts (GRB) by Imaging Atmospheric Cherenkov Telescopes opened up the possibility of Multi Messenger (MM) detection of neutron star merger events and the assiciated GRBs with Gravitational Waves (GW) and Very High Energy (VHE) gamma rays.
        New facilities with enhanced sensitivities which are under construction or will start construction in the near future will overlap their operations with the next Observing runs of the present generation or future projetcs of GW interferometric detectors creating the concrete chance for a combined detection.
        This talk will discuss the science potentials and the prospects with the next generation
        of instruments of a joint GW and VHE gamma ray detection.

        Speaker: Stefano Germani (Istituto Nazionale di Fisica Nucleare)
    • Closing remarks
    • 4:30 PM
      Coffee break