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Due to the current global COVID-19 situation, we have decided to convert the second edition of the Gravi-Gamma workshop to a virtual event. The workshop will take place from the 23rd to 25th of June 2021 from 7:00 am to 10:30 am PDT (4:00 pm to 7:30 pm CEST, 11:00 pm to 2:30 am JST). The virtual workshop will consist of invited talks and round table discussions.
Thanks to the recent groundbreaking observational results, Multi-messenger astrophysics is emerging as a distinct discipline with the great potential to provide insights into the properties and processes of the physical universe. This new discipline combines the complementary information carried by photons, gravitational waves, neutrinos, and cosmic rays about individual cosmic sources and source populations allowing to finally observe the astrophysical universe through all of the known forces of nature. In order to fully exploit the potential of this exciting new era it is imperative that the entire astrophysics community works together to share and discuss observational, modeling and theory results from every possible messenger. The second edition of the Gravi-Gamma workshop aims at bringing together experts in the fields of Multi-messenger instrumentation and data analysis, fundamental physics and cosmology to address the science potential with current and future detectors and the requirements for the future network for an optimal science exploration.
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
Melissa Pesce-Rollins
The spectacular detection of the first electromagnetic counterpart of a gravitational wave event detected by the LIGO/Virgo interferometers and originated by the coalescence of a double neutron star system (GW 170817) marked the dawn of a new era for astronomy. The short GRB 170817A associated to the GW event provided the long-sought evidence that at least a fraction of short GRBs are originated by NS-NS merging and suggested the intriguing possibility that relativistic jets can be launched in the process of a NS-NS merger. The wealth of data collected provided the first compelling observational evidence for the existence of “kilonovae”, i.e. the emission due to radioactive decay of heavy nuclei produced through rapid neutron capture. The extensive follow-up campaign carried out at all wavelengths over almost three years of GRB 170817A probed the GRB emission geometry, providing clear evidence for a successful jet endowed with an angular energy profile, featuring a narrow and energetic core (seen off-axis), surrounded by a slower, less energetic layer/sheath/cocoon. Besides the remarkable event associated to GW 170817, kilonova signatures have been tentatively identified in a few short GRBs light curves, supporting a scenario where kilonovae are ubiquitous and can probe neutron star mergers well beyond the horizon of the gravitational wave detectors.
In this talk I will review the situation and perspectives of our understanding of short GRBs (progenitors, central engine, emission geometry, environment) and kilonovae in the multi-messenger era.
I will briefly review some of the observational facts of Supernovae from the perspective of multi-messenger astronomy, such as neutrino and GW emissions.
We present a search for gamma-ray bursts in the Fermi-GBM 10 yr catalog that show similar characteristics to GRB 170817A, the first electromagnetic counterpart to a GRB identified as a binary neutron star (BNS) merger via gravitational wave observations. Our search is focused on a nonthermal pulse, followed by a thermal component, as observed for GRB 170817A. We employ search methods based on the measured catalog parameters and Bayesian Block analysis. Our multipronged approach, which includes examination of the localization and spectral properties of the thermal component, yields a total of 13 candidates, including GRB 170817A and the previously reported similar burst, GRB 150101B. The similarity of the candidates is likely caused by the same processes that shaped the gamma-ray signal of GRB 170817A thus providing evidence of a nearby sample of short GRBs resulting from BNS merger events. Some of the newly identified counterparts were observed by other space telescopes and ground observatories, but none of them have a measured redshift. We present an analysis of this subsample, and we discuss two models. From uncovering 13 candidates during a time period of ten years we predict that Fermi-GBM will trigger on-board on about one burst similar to GRB 170817A per year.
The search and study of the electromagnetic counterparts of gravitational wave signals requires the collaborative efforts of astrophysical researchers with different expertises and extending over the full range of the electromagnetic spectrum. This motivated the spontaneous constitution of GRAWITA, the GW INAF team, that, since the very beginning, was ready to react to alerts of LIGO-VIRGO interferometers. The successful story of the detection of the afterglow and kilonova after the binary NS merger GW170817 convinced even the skeptics of the exciting prospects of the new multi-messenger era.
However, the requirements of this new science are very demanding and therefore we promoted prompted the constitution of the ENGRAVE international collaborations that has the goal to facilitate the access to top optical/infrared observing facilities and to guarantee an effective team organisation.
While waiting for the incoming new LIGO/VIRGO/KAGRA runs, I will describe the challenges that we have to to address to meet the improved sensitivity of the GW interferometers. I will also summarises the ongoing attempts of the astronomical community to search for kilonovae regardless of the GW triggers.
In this talk I discuss the possibility that the low mass (2.50 ‒ 2.67 M⊙) companion of the 23 M⊙ black hole in the binary merger which produced GW190814 was a strange quark star. This possibility is viable if two families of compact stars, viz., “normal” neutron stars and strange quark stars, can coexist in nature, and neutron stars can get converted into strange quark stars.
The scenario with two coexisting families of compact stars could ease the tension between several observational data that seem to suggest the existence of very compact stars with radii smaller than about 12 km and masses of about 1.4 ‒ 1.5 M⊙ and the existence of more massive compact stars with radii up to about 15 ‒16 km. The latter circumstance could be realized in the case of the high mass (2.08 ± 0.08 M⊙) millisecond pulsar J0740+6620 as revealed by the recent measurement of its radius by the NICER Team (Miller et al, arXiv:2105.06979).
Newly-born millisecond magnetars are competing with black holes as source of the gamma-ray burst (GRB) power, mainly with their rotational energy reservoir. Since the GRB central engine remains hidden from direct electromagnetic observations, we discuss how the combined information provided by both the electromagnetic and gravitational signal are the most promising way to unveil its nature. The still unique case of GW 170817 / GRB 170817A could not provide any compelling evidence in favor of one of the two scenarios from the GW signal, thus this remains one of the major breakthrough achievable in the next future and with the next generation gravitational wave detectors.
Continuous gravitational waves (CWs) have not been detected so far, but their emission is expected from various astrophysical systems, like spinning neutron stars, if asymmetric with respect to their rotation axis, and clouds of ultra-light bosons that could form around Kerr black holes as a consequence of superradiance. In this talk I will report some of the most recent results obtained in the search of CWs using the data of LIGO and Virgo detectors, stressing the benefits of a multi-messenger approach, when feasible. Prospects for future runs will be also discussed.
Panel: Nicola Omodei, Maria Grazia Bernardini and Francesco Fidecaro
Hyper-Kamiokande is a next generation neutrino and nucleon decay experiment that is expected to start taking data in 2027. In this talk, I will introduce the experiment and give a brief update on its current status. I will then discuss its neutrino astronomy programme, with a special focus on supernova neutrinos.
The primary goal of a Neutrino Telescope is the search for astrophysical neutrinos in the TeV-PeV range. Several experimental activities have been developed aiming at the operation of a High Energy Neutrino Telescope: a detector sensitive to the Cherenkov light originated by the propagation, in a transparent medium, of relativistic charged particles generated by neutrino interactions. In the Baikal Lake (Siberia), at 1000m depths, a pioneer detector has been operated since 1990. In the last two decades the IceCube Detector, located at ~2000 m depth into the South Pole ice, and the ANTARES detector, anchored at 2400m depth in the Mediterranean Sea, have used the ice, and the sea water respectively, as transparent media where a matrix of photosensors, disposed according to well defined geometries, can measure the Cherenkov light. IceCube dimensions (about 1km3 of instrumented volume) exceed by about two order of magnitude the ANTARES ones. This last detector can be considered as the precursor of KM3NeT, the Mediterranean neutrino Telescope with cubic kilometre dimensions at present under construction. I will describe how neutrino astronomy can improve, in a multi-messenger scenario, our knowledge of the highest energy sources of cosmic rays, I will describe the most recent results obtained by existing detectors and the perspectives for the future.
The HAWC observatory has been taking continuous high-statistics measurements of TeV gamma rays and cosmic rays from two-thirds of the sky since commencing full operations in 2015. With its wide-angle survey capability, and a sensitivity to photon energies reaching over 100 TeV, HAWC is advancing studies of a diverse set of sources in the galactic plane, pushing the search for dark matter and physics beyond the Standard Model to unprecedented regimes, participating in a rapid, multi-wavelength and multi-messenger followup program for transient objects.
I will present highlights from the first five years of HAWC measurements that are highly complementary to those of the Fermi LAT telescope, highlighting the role of wide-angle surveys in the era of multi messenger astronomy.
Einstein Telescope (ET) is the pan-European project aiming to the realisation of a new generation gravitational wave observatory. ET promises a gain in sensitivity from one to some orders of magnitude with respect the current advanced detectors, with a particular attention at the low frequency band, below 10Hz. In order to achieve these performances, an innovative design and an intense technology development programme are implemented. Several are the science targets identified for ET, in astrophysics, multimessenger astronomy, nuclear and fundamental physics attracting a large and diverse scientific community in to the project. An overview of the ET project, of the technology, of the science targets and of the whole realisation process will be presented.
The next decade of Universe exploration is expected to undergo a revolution for the transient astrophysics. The third generation of gravitational-wave (GW) observatories, such as Einstein Telescope (ET) and Cosmic Explorer (CE) will allow us for the first time to observe GWs along the cosmic history back to the cosmological dark ages. These observatories will be an unprecedented resource to address open questions of fundamental physics, astrophysics and cosmology. They will operate in synergy with a new generation of innovative electromagnetic (EM) observatories, such as CTA, Athena, the Vera Rubin Observatory, JWST, ELT, SKA and the mission concepts THESEUS and HERMES. This network of observatories will probe the formation, evolution and physics of binary systems of compact object in connection with kilonovae and short gamma-ray bursts along with the star formation history and chemical evolution of the Universe. The talk will summarize the multi-messenger science case for ET and the perspectives for the next decade.
Very-high-energy (VHE) gamma-ray astroparticle physics is a relatively young field, and observations over the past decade have surprisingly revealed almost two hundred VHE emitters which appear to act as cosmic particle accelerators. These sources are an important component of the Universe, influencing the evolution of stars and galaxies. At the same time, they also act as a probe of physics in the most extreme environments known - such as in supernova explosions, and around or after the merging of black holes and neutron stars. However, the existing experiments have provided exciting glimpses, but often falling short of supplying the full answer. A deeper understanding of the TeV sky requires a significant improvement in sensitivity at TeV energies, a wider energy coverage from tens of GeV to hundreds of TeV and a much better angular and energy resolution with respect to the currently running facilities. The next generation gamma-ray observatory, the Cherenkov Telescope Array (CTA), is the answer to this need. In this talk I will present the scientific capabilities of this future facility that will allow to address in detail many of the still open questions of the gamma-ray astrophysics. In addition, CTA will allow the entire astronomical community to explore a new discovery space that will likely lead to paradigm-changing breakthroughs. In particular, CTA has an unprecedented sensitivity to short (sub-minute) timescale phenomena, placing it as a key instrument in the future of multi-messenger and multi-wavelength time domain astronomy. In the talk I will cover the main science cases that will strongly benefit from coordinated observations with other facilities, from gravitation waves detectors, to neutrino telescopes and astronomical observatories operating at all wavelengths.
What is now referred to as multi-messenger and multi-frequency astrophysics has been at the very basis of the investigation of Cosmic Rays for many decades now: the spectrum and morphology of Galactic gamma ray and radio emission have represented powerful tools to unveil the origin of the cosmic radiation. Neutrinos and gravitational waves have recently joined the scene. The recent measurement of a flux of neutrinos of astrophysical origin has now added one actor to the list of messengers that tell us the tale of the acceleration and transport of cosmic rays. Surprises are not rare: I will discuss a few instances of information coming from gamma rays and neutrinos that are potentially affecting our way of thinking of cosmic rays, on galactic and extragalactic scales.
Panel: Michele Punturo, Marica Branchesi and Elizabeth Ferrara
Following detection by advanced LIGO and Virgo, gravitational wave (GW) stocks are
on the rise. Despite their enormous impact, ground based detectors are
only sensitive to GW sources in the audio band. The low frequency GW
Universe is still unexplored and future spaceborne interferometers such
as LISA and ongoing and future pulsar timing arrays (PTAs) have the
potential to probe this window from nHz to mHz, unveiling the
gravitational universe and its sources, in particular massive black hole
binaries (MBHBs). Forming in the aftermath of galaxy mergers, those
sources are expected to be the loudest in the GW universe and possibly
bright in the electromagnetic (EM) spectrum. I will discuss the expected
joint GW and EM emission of MBHBs and future opportunities for
multimessenger observations with LISA and PTA and future EM facilities
such as LSST, SKA, Athena.
The detection of the electromagnetic (EM) emission following the gravitational wave (GW) event GW170817 opened the era of multi-messenger astronomy with GWs and provided the first direct evidence that at least a fraction of binary neutron star (BNS) mergers are progenitors of short Gamma-Ray Bursts (GRBs). GRBs are also expected to emit very-high-energy (VHE, > 100 GeV) photons, a prediction that has been confirmed by recent MAGIC and H.E.S.S. observations. One of the challenges for future multi-messenger observations will be the detection of such VHE emission from GRBs in association with GWs.
In this talk I will review the challenges and the status of the searches for VHE EM counterparts to GWs and discuss the prospects for future detections with next generation instruments such as the Cherenkov Telescope Array. The implications that future joint GW and VHE EM observations could have on the understanding of GRB physics will also be discussed.
The last five years marked the birth of the first detections of gravitational waves and neutrinos from outside the solar system opened the era of multi-messenger astrophysics. In addition to the growing and continuously upgraded GW and neutrino facilities, many observatories in the e.m. domain (opticla, NIR, radio, X- and gamma-rays, VHE) worldwide are already partly or fully dedicated to the study of the Universe this amazing newly open window. But it is towards the end of this decade, and the beginning of the '30s that we will actually enter the golden-age of multi-messenger astrophysics. Indeed, as I will review in this talk, the projects for advanced second generation and third generation GW and neutrino detectors (e.g., ET, CE, KM3NeT) are flanked by the current development of the extremely large observatories in the electro-magnetic domain (e.g., E-ELT, TMT, SKA, Athena, CTA) and dedicated space mission concepts like THESEUS (ESA/M5 candidate). The synergies between these great ground and space facilities will revolutionise several fields of astrophysics and provide measurements of paramount importance also for cosmology and fundamental physics.
I will give a broad overview of the scientific targets of the Einstein Telescope in astrophysics, cosmology, and fundamental physics
Extreme astrophysical events can send us physical information through complementary messengers of different nature:
gravitational waves (GW), electromagnetic radiation, neutrinos or other particles.
On August 17th 2017, the first multi-messenger astrophysical source (GW170817) was revealed,
thanks to the coordinated action of gravitational wave detectors, gamma ray burst monitors and optical and radio telescopes,
which gave us a complete picture of the coalescence of two neutron stars.
With 3rd Generation gravitational wave detectors and the new astronomical facilities (LSST, ELT, SKA, CTA, KM3NET),
we expect many events like that. We anticipate the need to analyse the data provided to us by such events, to fulfill
the requirements of real-time analysis, but also in order to decipher the event in its entirety.
The use of machine and deep learning techniques has become increasingly common in scientific communities.
The large amount of data to analyze and the need for real-time analysis are driving the search for cutting-edge techniques
and new data analysis paradigms. Especially the field of deep learning for event-based, image-based and signal-based applications
of two and higher dimensions has been intensively followed by expert groups within the ESFRIs and will be deployed to the EOSC via ESCAPE.
The discovery of the binary neutron star merger GW170817 electromagnetic counterparts has opened the era of gravitational wave+electromagnetic (GW+EM) multi-messenger astronomy.
Exploiting this breakthrough requires increasing samples to explore the diversity of the GW electromagnetic counterparts behavior, provide tighter constraints on the Hubble constant, and test fundamental physics.
Rubin-LSST will play a key role in the newborn multi-messenger astronomy field allowing us to study and identify the likely faint and rapidly fading electromagnetic counterparts of the hundreds of gravitational wave (GW) events expected by the 2nd generation GW detectors network at full sensitivity. It will operate in synergy with other multi-wavelength facilities, available for our team GRAWITA expressly dedicated to this project.
In this talk, I will present the activities we carried out to optimize the response of the Italian GRAWITA network of facilities to expected GW triggers and how GRAWITA is working in the context of the search for GW counterparts with Rubin-LSST. All the activities I will describe are expected to provide means and opportunities to the Italian and European astronomical communities to have a leading role in the GW and Time Domain Astronomy.
Panel: Federico Ferrini, Luca Latronico and Pasquale Blasi