Noname manuscript No. (will be inserted by the editor)
Multi-Messenger Astrophysics with THESEUS in the 2030s
Riccardo Ciolfi · Giulia Stratta · Marica Branchesi · Bruce Gendre · Stefan Grimm · Jan Harms · Gavin Paul Lamb · Antonio Martin-Carrillo · Ayden McCann · Gor Oganesyan · Eliana Palazzi · Samuele Ronchini · Andrea Rossi · Om Sharan Salafia · Lana Salmon · Stefano Ascenzi · Antonio Capone · Silvia Celli · Simone Dall’Osso · Irene Di Palma · Michela Fasano · Paolo Fermani · Dafne Guetta · Lorraine Hanlon · Eric Howell · Stephane Paltani · Luciano Rezzolla · Serena Vinciguerra · Angela Zegarelli · Lorenzo Amati · Andrew Blain · Enrico Bozzo · Sylvain Chaty · Paolo D’Avanzo · Massimiliano De Pasquale · Husne¨ Dereli-Begu´ e´ · Giancarlo Ghirlanda · Andreja Gomboc · Diego Gotz¨ · Istvan Horvath · Rene Hudec · Luca Izzo · Emeric Le Floch · Liang Li · Francesco Longo · S. Komossa · Albert K. H. Kong · Sandro Mereghetti · Roberto Mignani · Antonios Nathanail · Paul T. O’Brien · Julian P. Osborne · Asaf Pe’er · Silvia Piranomonte · Piero Rosati · Sandra Savaglio · Fabian Schussler¨ · Olga Sergijenko · Lijing Shao · Nial Tanvir · Sara Turriziani · Yuji Urata · Maurice van Putten · Susanna Vergani · Silvia Zane · Bing Zhang
Received: date / Accepted: date
Riccardo Ciolfi 3, 20126 Milano, Italy INAF, Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio Stefano Ascenzi 5, I-35122 Padova, Italy; INFN, Sezione di Padova, Via Francesco Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Marzolo 8, I-35131 Padova, Italy Magrans s/n, 08193, Barcelona, Spain; Institut d’Estudis Espacials de E-mail: riccardo.ciolfi@inaf.it Catalunya (IEEC), Carrer Gran Capita 2-4, 08034 Barcelona, Spain Giulia Stratta Antonio Capone, Silvia Celli, Irene Di Palma, Michela Fasano, Paolo INAF, Osservatorio di Astrofisica e Scienza dello Spazio, via Piero Go- Fermani, Angela Zegarelli betti 93/3, 40129 Bologna, Italy; INFN, Sezione di Firenze, via San- Dipartimento di Fisica dell’Universita` La Sapienza, P.le Aldo Moro 2, sone 1, I-50019, Firenze, Italy I-00185 Rome, Italy; INFN, Sezione di Roma, P.le Aldo Moro 2, I- Marica Branchesi, Stefan Grimm, Jan Harms, Gor Oganesyan, 00185 Rome, Italy Samuele Ronchini Simone Dall’Osso Gran Sasso Science Institute, Viale F. Crispi 7, I-67100 L’Aquila (AQ), Gran Sasso Science Institute, Viale F. Crispi 7, I-67100 L’Aquila (AQ), Italy; INFN, Laboratori Nazionali del Gran Sasso, I-67100 Assergi, Italy Italy Dafne Guetta Bruce Gendre, Ayden McCann, Eric Howell ORT-Braude College, Carmiel, Israel OzGrav-UWA, University of Western Australia, 35 Stirling Highway, M013, 6009 Crawley, WA, Australia Stephane Paltani Department of Astronomy, University of Geneva, 1205 Versoix, Gavin Paul Lamb, Andrew Blain, Paul T. O’Brien, Julian P. Osborne, Switzerland Nial Tanvir Luciano Rezzolla
arXiv:2104.09534v1 [astro-ph.IM] 19 Apr 2021 School of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK Institut fur¨ Theoretische Physik, Max-von-Laue-Strasse 1, D-60438 Frankfurt, Germany; Frankfurt Institute for Advanced Studies, Ruth- Antonio Martin-Carrillo, Lana Salmon, Lorraine Hanlon Moufang-Strasse 1, D-60438 Frankfurt, Germany; School of Mathe- School of Physics and Centre for Space Research, University College matics, Trinity College, Dublin 2, Ireland Dublin, Dublin 4, Ireland Serena Vinciguerra Eliana Palazzi, Andrea Rossi, Lorenzo Amati Anton Pannekoek Institute for Astronomy, University of Amsterdam, INAF, Osservatorio di Astrofisica e Scienza dello Spazio, via Piero Go- Science Park 904, 1090GE Amsterdam, The Netherlands betti 93/3, 40129 Bologna, Italy Enrico Bozzo Om Sharan Salafia, Paolo D’Avanzo, Giancarlo Ghirlanda Department of Astronomy, University of Geneva, Chemin d’Ecogia 16, INAF, Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 CH-1290 Versoix, Switzerland Merate, Italy; INFN, Sezione di Milano-Bicocca, Piazza della Scienza 2 Riccardo Ciolfi et al.
Abstract Multi-messenger astrophysics is becoming a ma- tral role during the 2030s in detecting and localizing the jor avenue to explore the Universe, with the potential to span electromagnetic counterparts of gravitational wave and neu- a vast range of redshifts. The growing synergies between dif- trino sources that the unprecedented sensitivity of next gen- ferent probes is opening new frontiers, which promise pro- eration detectors will discover at much higher rates than the found insights into several aspects of fundamental physics present. Here, we review the most important target signals and cosmology. In this context, THESEUS will play a cen- from multi-messenger sources that THESEUS will be able to detect and characterize, discussing detection rate expec- Sylvain Chaty tations and scientific impact. Universite´ de Paris and Universite´ Paris Saclay, CEA, CNRS, AIM, F-91190 Gif-sur-Yvette, France; Universite´ de Paris, CNRS, AstroPar- Keywords multi-messenger astrophysics · gamma-ray ticule et Cosmologie, F-75013 Paris, France burst · compact binary merger · kilonova · X-ray sources · Massimiliano De Pasquale neutrino sources Department of Astronomy and Space Sciences, Istanbul University, Beyazıt 34119, Istanbul, Turkey Antonios Nathanail Husne¨ Dereli-Begu´ e´ Department of Physics, National and Kapodistrian University of Max Planck Institute for Extraterrestrial Physics, Giessenbachstrasse Athens, Panepistimiopolis, GR 15783 Zografos, Greece 1, D-85748 Garching, Germany; Department of Physics, Bar-Ilan Uni- Asaf Pe’er versity, Ramat-Gan 52900, Israel Department of Physics, Bar-Ilan University, Ramat-Gan 52900, Israel Andreja Gomboc Silvia Piranomonte Center for Astrophysics and Cosmology, University of Nova Gorica, INAF, Osservatorio Astronomico di Roma, via Frascati 33, I-00078 Vipavska 13, SI-5000 Nova Gorica, Slovenia Monte Porzio Catone (RM), Italy Diego Gotz¨ Piero Rosati AIM-CEA/DRF/Irfu/Departement´ d’Astrophysique, CNRS, Univer- Department of Physics and Earth Sciences, University of Ferrara, Fer- site´ Paris-Saclay, Universite´ de Paris, Orme des Merisiers, F-91191 rara, Italy Gif-sur-Yvette, France Sandra Savaglio Istvan Horvath Physics Department, University of Calabria, via P. Bucci, 87036 University of Public Service, Budapest, Hungary Rende, Italy Rene Hudec Fabian Schussler¨ Czech Technical University in Prague, Faculty of Electrical Engineer- IRFU, CEA, Universite´ Paris-Saclay, F-91191 Gif-sur-Yvette, France ing, Prague, Czech Republic; Astronomical Institute, Czech Academy of Sciences, Ondrejov, Czech Republic; Kazan Federal University, Olga Sergijenko Kazan, Russian Federation Astronomical Observatory of Taras Shevchenko National University of Kyiv, Observatorna str. 3, Kyiv 04053, Ukraine; Main Astronomical Luca Izzo Observatory of the National Academy of Sciences of Ukraine, Zabolot- DARK, Niels Bohr Institute, University of Copenhagen, Lyngbyvej 2, noho str. 27, Kyiv 03680, Ukraine 2100 Copenhagen, Denmark Lijing Shao Emeric Le Floch Kavli Institute for Astronomy and Astrophysics, Peking University, Laboratoire AIM, CEA/DSM/IRFU, CNRS, Universite´ Paris-Diderot, Beijing 100871, China; National Astronomical Observatories, Chinese Bat. 709, 91191 Gif-sur-Yvette, France Academy of Sciences, Beijing 100012, China Liang Li Sara Turriziani ICRANet, Piazza della Repubblica 10, I-65122 Pescara, Italy Physics Department, Gubkin Russian State University, 65 Leninsky Francesco Longo Prospekt, Moscow 119991, Russian Federation Universita` degli Studi di Trieste, via Valerio 2, I-34127 Trieste, Italy; Yuji Urata INFN, Sezione di Trieste, via Valerio 2, I-34127 Trieste, Italy; Institute Institute of Astronomy, National Central University, Chung-Li 32054, for Fundamental Physics of the Universe (IFPU), I-34151 Trieste, Italy Taiwan S. Komossa Maurice van Putten Max-Planck Institut fur¨ Radioastronomie, Auf dem Hugel¨ 69, 53111 Physics and Astronomy, Sejong University, 98 Gunja-Dong Gwangin- Bonn, Germany gu, Seoul 143-747, Korea; OzGrav-UWA, University of Western Aus- Albert K. H. Kong tralia, 35 Stirling Highway, M013, 6009 Crawley, WA, Australia Institute of Astronomy, National Tsing Hua University, Hsinchu Susanna Vergani 30013, Taiwan GEPI, Observatoire de Paris, PSL University, CNRS, Place Jules Sandro Mereghetti Janssen, 92190 Meudon, France INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica, Via A. Corti Silvia Zane 12, I-20133 Milano, Italy Mullards Space Science Laboratory, University College London, Roberto Mignani Holmbury St Mary, Dorking, Surrey, RH56NT, UK INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica, Via A. Corti Bing Zhang 12, I-20133 Milano, Italy; Janusz Gil Institute of Astronomy, Univer- Department of Physics and Astronomy, University of Nevada Las Ve- sity of Zielona Gora,´ ul Szafrana 2, 65-265, Zielona Gora,´ Poland gas, Las Vegas, NV 89154, USA Multi-Messenger Astrophysics with THESEUS in the 2030s 3
1 Introduction decision/construction operation Gravitational 2G Expected extension waves The breakthrough discoveries of the last few years have demon- strated the great scientific potential of gravitational wave 3G (GW) astronomy and of multi-messenger astrophysics with GW and neutrino sources. Since the first detection of GWs Neutrinos in 2015 from coalescing binary black hole (BH-BH) sys- IceCube-Gen2 tems [1,2], tens of additional stellar-mass black hole coa- lescences [3] as well as two confirmed binary neutron star KM3NeT (NS-NS) mergers and at least one possible NS-black hole
(NS-BH) merger [4,5,6] have been detected so far with Ad- THESEUS vanced LIGO [7] and Advanced Virgo [8]. These observa- tions likely represent only the tip of the iceberg and have 2025 2028 2031 2033 2036 confirmed the expectation that compact binary coalescences Fig. 1 THESEUS nominal 4-year operation window along with the (CBCs) would represent the most common GW sources at current timeline of major facilities for neutrino and GW observations the high frequencies where ground-based GW detectors are by the end of the 2020s and the first half of 2030s, namely: the second- generation (2G) GW interferometer network ([15]; GWIC Roadmap sensitive (i.e. from ∼ 10 Hz up to a few kHz). At such fre- [22], https://gwic.ligo.org/), the third-generation GW in- quencies, there are also other potentially detectable terferometers Einstein Telescope (ET; [23], et-gw.eu) and Cosmic GW sources, including core-collapsing massive stars as well Explorer (CE; [16]), and the neutrino observatories IceCube-Gen2 [24] as rotating and/or bursting NSs, whose output in GWs is and KM3NeT (ESFRI Roadmap 2018, http://roadmap2018. esfri.eu). however more uncertain with respect to CBCs (e.g., [9,10]). All these high-frequency GW sources (possibly includ- ing stellar-mass BH-BH coalescences in rare circumstances; [20], or SVOM [21] are still expected to be rare and likely 1 e.g., [11]) are expected to emit a variety of bright electro- less than one per year for geometrical reasons . magnetic (EM) signals over the entire spectrum, from radio About ten times more sensitive, third generation (3G) to gamma-rays (see Sections 2, 3), offering opportunities for ground-based GW interferometers, such as the Einstein Tele- a multi-messenger investigation. The first GW detection of scope (ET; e.g., [23,25]) and Cosmic Explorer (CE; e.g., a NS-NS coalescence on August 17th 2017 [4], accompa- [16]), are being planned for operation starting in the first nied by the observation of the short gamma-ray burst (GRB) half of the 2030s, allowing us to observe CBCs at distances 170817A [12], the optical/infrared kilonova AT2017gfo, and nearly ten times farther with respect to the 2G network (see further X-ray, optical, infrared, and radio emission ([13] and Figure 1). This will significantly boost the detection rates refs. therein), provided a first striking example of what can for CBCs and, at the same time, greatly enhance the detec- be accomplished by combining together the information from tion chances for the other types of fainter GW sources in the these two distinct channels (see also Section 2). nearby Universe. However, the next generation of ground- During the next few years, the aLIGO and AdVirgo will based GW interferometers will have relatively poor sky lo- reach their design sensitivity and together with the first un- calisation capabilities for the vast majority of detected GW derground GW interferometer KAGRA in Japan [14], which sources, implying serious difficulties in the identification of recently joined the network, they will ensure an increase in the EM counterparts. For instance, a network composed by CBC detection rates and an improvement in source local- ET and all the 2G detectors will localize within a sky area 2 10 − 20 ization [15]. By the end of the 2020s, further upgrades on below 100 deg only % of NS-NS coalescences at z ' 0.3 aLIGO (A+ and Voyager [16]) and AdVirgo (Virgo+) are (e.g., [26,25]). planned to be completed and the GW sky will be routinely Key discoveries have also been made in neutrino astron- monitored with the final second-generation (2G) GW detec- omy during the last decade, with at least two major results: tor network, composed by five interferometers with the ad- (i) a diffuse flux of astrophysical very-high-energy neutri- dition of LIGO-India, a clone of the two LIGO detectors nos (10 TeV-10 PeV) detected by IceCube [27], the ori- [15]. The distances up to which CBCs will be detected by gin of which is still to date unknown (e.g., [28]); (ii) the the 2G network will go from few hundreds of Mpc to few possible identification of a neutrino cosmic source with the Gpc [15]. Within such distances, the expected 2G network 1 Only a small fraction of NS-NS coalescences will be face-on, detection rate of NS-NS coalescences, i.e. the most promis- i.e. with their orbital angular momentum nearly directed along the line ing multi-messenger sources, could be as high as 80/yr [15]. of sight (within a few degrees). Even assuming a very high jet pro- Nonetheless, joint short GRB observations by current and duction efficiency from such systems, most of the corresponding short GRBs will be beamed away from us. The possible detection of “off- future high-energy missions that will be operational during axis” or “misaligned” short GRBs, like in the case of GRB 170817A, the 2020s as, e.g., Swift [17], Fermi [18,19], INTEGRAL will remain limited to very near (and very rare) events. 4 Riccardo Ciolfi et al. blazar TXS0506+056 [29], which adds to the only two pre- IR telescope (IRT) as well as other space and ground- viously known sources of neutrinos, both belonging to the based narrow field instruments. Sky coordinates can be Local Group environment, i.e. the Sun and the supernova disseminated to the astronomical community within min- SN 1987A. Among the most promising candidates for the utes. diffuse neutrinos, GRBs, AGNs, and star bursting galaxies – In case of detection of the NIR/optical counterpart by are of particular relevance and, for those, multi-messenger IRT, in response to an SXI/XGIS trigger, disseminated observations will be crucial to achieve the sensitivity level sky coordinates will be accurate at the arcsecond level. required by detection, thanks to the possibility of explor- This fundamental input will make it possible to trigger ing spatial correlations as well as temporal coincidences in deeper follow-up observations with the very large ground- the case of transient events (see Section 4). Looking ahead and space-based telescopes available in the early 2030s, towards the future multi-messenger campaigns, larger vol- such as SKA, CTA, ELT, or Athena, which will further ume detectors are being planned, in particular gigaton wa- boost the scientific return in terms of GW and/or neu- ter Cherenkov telescopes such as KM3NeT in the Mediter- trino source characterization. ranean Sea [30] and IceCube-Gen2 at the South Pole [24] – The high cadence spectral observations across the wide (see also [31,32]). In the early 2030s, these detectors will be range 0.3 keV−20 MeV (SXI + XGIS), possibly with completed, accessing the level of fluxes expected from cos- additional NIR coverage (IRT), will represent a great mic sources (Figure 1). Their sky localisation capabilities advantage for the identification and characterization of will however remain rather limited (e.g., [33] and refs. therein). the diverse EM counterparts of GW and neutrino sources In order to maximise the science return of the multi- with respect to other all sky monitors that are limited to messenger investigations during the 2030s, it will be essen- a narrower band, such as the forthcoming Chinese mis- tial to have a facility that can both (i) detect, localize, and sion, Einstein Probe (0.3−4 keV). disseminate the EM counterpart signals independently from – In response to THESEUS triggers, the search for sub- the GW/neutrino events and, at the same time, (ii) rapidly threshold events in GW and neutrino archival data will cover with good sensitivity the large compatible sky areas also be enabled (e.g., in case of a GRB trigger). Such a provided by GW or neutrino detections. Moreover, given the strategy has been already pursued by the current LIGO- lack of precise knowledge about the properties of various Virgo Collaboration for a number of detected GRBs (e.g., EM counterparts of both GW and neutrino sources, (iii) a [34]). large spectral coverage is another essential capability. These The next Sections describe the main expected EM coun- combined requirements are uniquely fulfilled by the Tran- terparts that THESEUS will be able to detect in synergy sient High-Energy Sky and Early Universe Surveyor (THE- with the future GW and neutrino facilities, both in Survey SEUS).2 mode and via Target of Opportunity programs. In Section 2, THESEUS will allow us to monitor the transient sky we focus on the EM counterparts of NS-NS and NS-BH with a number of advantages with respect to previous mis- mergers, representing the most promising GW and multi- sions, yielding a significant step forward in our ability to messenger sources. Section 3 is devoted to GW sources with investigate the multi-messenger Universe: detectable EM counterparts other than merging compact bi- – A large fraction of poorly localised multi- messenger naries. Then, we complete the discussion on EM counter- sources will be independently discovered with the THE- parts that THESEUS will be able to detect independently SEUS XGIS and SXI within one orbit, due to the un- from an external trigger (Survey mode) with the most promis- precedented combination of large field-of-view (XGIS: ing multi-messenger neutrino sources (Section 4). EM coun- 2 sr in the 2 − 150 keV energy range and > 4 sr at > terparts detectable by THESEUS in response to external trig- 150 keV; SXI: 0.5 sr) and grasp (i.e. the product of effec- gers are discussed in Section 5, while we draw our conclu- tive area and FoV) of these instruments. This will enable sions in Section 6. independent triggers on EM counterparts of numerous GW/neutrino sources, as it was the case for GRB 170817A triggered by Fermi/GBM independently from the GW 2 Electromagnetic counterparts from NS-NS and detection of the same source. At the same time, XGIS NS-BH mergers and SXI will provide fairly accurate localisation (<150), which is a missing feature in Fermi/GBM. This will al- NS-NS and NS-BH mergers are among the most promis- low for follow-up observations with the onboard 0.7 mt ing high-frequency GW sources (for ground-based interfer- ometers) from which we expect a variety of detectable EM 2 https: We refer to the THESEUS Assessment Study Report ( counterparts. From short GRBs to other X-ray and IR sig- //sci.esa.int/s/8Zb0RB8) for a general introduction on the space mission, the on-board instruments (XGIS, SXI, IRT), and the nals accompanying these merger events, we discuss here the key scientific objectives. main EM counterparts that THESEUS will be able to detect. THESEUS Assessment Study Report page 20
Multi-Messenger Astrophysics with THESEUS in the 2030s 5
2.1 Short gamma-ray bursts Compact binary coalescences (CBCs) have been confirmed as the The NS-NS merger detected with LIGO and Virgo on Au- most promising GW emitters in the frequency range covered by gust 17, 2017 (GW170817) and its associated short GRB 170817A was the first direct evidence of the progeni- ground-based detectors (i.e. from about 10 Hz up to few kHz). Since tor of a short GRB as a compact binary merger system [12, the first GW detection of a coalescing binary stellar-mass black hole 35,36,37,38,39,40,41,42,43,44,45,46] (see, e.g., [47] for a review), which confirmed several indirect pieces of evi- (BH-BH) system in 2015 [47], numerous other BH-BH mergers ( [48], dence collected in the last decade (e.g., [48,49]). The after- [49]), two confirmed binary neutron star (NS-NS) mergers, and one glow properties of GRB 170817A also confirmed the formation of a relativistic, possible NS-BH merger ( [50], [51], [52]) have been detected so far narrow jet (half-opening angle of about 2 − 4 deg [45,46]) with Advanced LIGO (aLIGO, [53]) and Advanced Virgo (AdV, after the NS-NS merger, a result that theoretical studies and MHD simulations could not fully predict. It was also the first [54]). CBCs are also sources of potentially detectable electromagnetic short GRB viewed from outside the core of the jet (i.e. the (EM) radiation across the whole spectrum, from radio to gamma-rays. cone with very high Lorentz factor), as demonstrated by the rising and then slowly decaying afterglow. The viewing an- A breakthrough confirmation of such expectations was obtained on gle was estimated to be around 15−30 deg away from the di- August 17th, 2017, when a GW signal consistent with a NS-NS merger rection of propagation of the highly relativistic jet core [45, 46]. Such a lateral view, allowed to identify the observed 40 Mpc away (GW170817) was accompanied by the short gamma-ray gamma-ray emission as directly originating from the mildly burst GRB 170817A and later by further X-ray, optical, infrared, and relativistic cocoon that formed around the jet core via the in- teraction of the incipient jet itself with the surrounding ma- radio emission ( [55], [56]). This event was the first direct evidence of terial ejected during and after the NS-NS merger. Figure 2 Fig. 2 Schematic cartoon depicting the different emitting regions the progenitor of a short GRB, confirming past indirect evidence. The depicts our current understanding of NS-NS merger emit- responsible for the EM counterparts of the multi-messenger event ting regions, as gathered from the single multi-messenger FigureGW170817/GRB 2-12 170817A, Cartoon based on our on current the understanding current of afterglow properties confirmed the formation of a relativistic, narrow observation of the August 2017 event. the physical processes accompanying the 2017 NS-NS merger. [From [50]] The above results clearly show how the detection of short understanding of NS-NS merger emitting jet after the NS-NS merger (half-opening angle of ~2°-4°, [57]), a GRBs is of crucial relevance for multi-messenger astrophysics regions supported by the multi- result that theoretical studies and magneto hydro-dynamic simulations and underline the fundamental role of THESEUS in ensur- ing short GRB observations during the 2030s, when the cur- messenger observation of GW170817 could not fully predict. Optical/NIR observations showed the first firm rent and future space missions as Fermi, Swift, or SVOM /GRB170817obtained by considering, (from at each [46]). redshift, the GW detection evidence of a kilonova (KN), with two (“blue” and “red”) main are not guaranteed and, at the same time, both 2G and 3G efficiency for NS-NS mergers. In these computations, three emission components [58]. It was also the first GRB viewed from GW interferometers are expected to be operational. scenarios for the 3G GW interferometers have been con- During its nominal mission lifetime, THESEUS/XGIS sidered:outside 1) ET the alone, core 2) ET of plus the one jet CE (in(i.e. USA), the 3) ETcone with very high Lorentz factor), as demonstrated by the rising and then 0 and SXI are expected to detect and accurately (< 15 ) lo- plusslowly two CEs decaying (one in USA andafterglow one in Australia). [59]. The The ex- viewing angle has been estimated to be around 15°-30° away from the calize ' 40 short GRBs (' 12/yr assuming 3.45 years of pected numbers of short GRBs detected and localized with scientific observations) inside their imaging field of view, THESEUSdirection and of detected propagation also by 2G and of 3G the interferome- highly relativistic jet core [57]. Such a lateral view allowed us to identify the plus numerous short GRBs at higher energies (> 150 keV) ters are summarized in Table 1. These conservative numbers with coarse or no sky localization. These numbers are ob- areobserved robust and based gamma-ray on the Mission emission Observation Simulator as directly originating from the mildly relativistic cocoon formed around the jet tained from simulations of a realistic observational sequence (MOS)core resultsvia 3theand interaction state-of-the-art NS-NS of the merger incipient simula- jet itself with the surrounding material ejected during and after the NS- of THESEUS, considering all observational constraints, in tions for the GW detection efficiency estimates. response to a random set of short GRB triggers based on the NS merger (Figure 2-12). 3 population model of [51]. Such a population model is built By considering the possibility to observe short GRBs on short GRBs observed before GRB 170817A with Swift alsoThe outside last the decade solid angle of has the narrow also jet seen core, the decisive num- discoveries in neutrino astronomy. The two major results are: the and Fermi, for which the line of sight falls inside the narrow ber of potential detections can sensibly increase. Indeed, 4 detection of a diffuse flux of astrophysical very-high-energy neutrinos (10 TeV-10 PeV) by IceCube [60], core of the corresponding jet (i.e. “aligned”). Figure 3 (left the misaligned view of GRB 170817A enabled us for the panel) shows the redshift distribution of these short GRBs firstwhose time to quantify origin how is the still high-energy unknown prompt emission ( [61], [62]); and the first possible identification of a neutrino source at (blue line). Joint short GRB+GW detections are also shown, becomescosmological gradually softer distance, and less energetic the as blazar the view- TXS0506+056 [63] which adds to the only known non-solar source of ing angle increases (with respect to the jet axis). As a re- 3 For more details, see the THESEUS Assessment Study Report (https://sci.esa.int/s/8Zb0RB8). sult,neutrinos, it has been possible the to supernova estimate, for events SN1987A similar to in the Local Group environment. These detections together with 4 We note that other population models for aligned short GRBs exist GRBGW170817 170817A, the maximumshow viewingthe huge angle at power which a given of identifying an electromagnetic counterpart of a GW or neutrino source. in the literature (e.g., [52]). instrument could detect the prompt emission depending on By the end of the 2020s, the network of second generation (2G) GW interferometers, with Advances LIGO Plus (A+), Advanced VIRGO Plus (AdV+) and KAGRA [64], will see further upgrades and the addition of a fifth interferometer, LIGO-India, expected to start observations in 2025 [65]. The distances2 up to which NS- NS and 10-solar-mass BH-BH mergers will be detected by the completed 2G network will be ~330 Mpc and ~2.6 Gpc, respectively. Within such distances, the expected detection rate of the most promising EM radiation emitters, NS-NS mergers, is in the range ~1-80 per year (updated to O3 results, [65]). Joint observations of short GRBs (as in the case of GW 170817) by current and future missions that will fly during the 2020s, like Fermi, INTEGRAL, or SVOM, are expected to be rare and likely much less than one per year due to the beamed emission even assuming a high jet production efficiency from such systems.
2This is defined as the distance enclosing the CBC orientation-averaged spacetime volume surveyed per unit detector time, assuming a matched-filter detection signal-to-noise ratio (SNR) threshold of 8 in a single detector [65].
THESEUS Assessment Study Report page 23
Table 2-2 THESEUS role in the context of multi-messenger astrophysics during the 2030s The role of THESEUS THESEUS vs other facilities EM follow-up The large XGIS and SXI FoV and grasp will allow THESEUS will independently detect the short GRB signal, challenges: THESEUS to independently trigger the EM counterparts similarly to Fermi/GBM for the case of GRB 170817A, but of several GW/neutrino sources and localize them down with respect to the Fermi/GBM, THESEUS will also provide The poor sky to arcmin/arcsec level. accurate localisation down to the arcmin/arcsecond-level. localizations of GW/neutrino The high cadence spectral observations across 0.3 keV - THESEUS large spectral coverage is an advantage for cosmic sources 10 MeV plus possible additional NIR observations, will transient identification w.r.t. other high-energy all-sky during the ‘30s allow to identify the nature of EM counterparts of GW monitors operating on narrower energy bands, as e.g., challenge and neutrino sources Einstein Probe (0.3-4 keV) which is not optimized for the searches for the detection of short GRBs. EM counterparts and their THESEUS will disseminate accurate sky localization The synergies of THESEUS with next generation neutrino identification (arcmin/arcsecond uncertainties) within and GW observatories will significantly increase the number and/or full seconds/minutes to the astronomical community, thus of multi-messenger detections, allowing us to apply a first characterization enabling large ground- and space-based telescopes statistical approach to the study of multi-messenger sources in the EM available by 2030s as SKA, CTA, ELT, ATHENA, etc. and thus representing a major step forward with respect to spectrum to observe and deeply characterise the nature of the other missions operating during the 2020s GW/neutrino source as well as increasing the scientific 6 output of these facilities. Riccardo Ciolfi et al.
Fig. 3 Left: The redshift distribution of well-localized aligned short GRBs (blue) from XGIS and SXI and those detected also with IRT (25%, Figureindigo). 2-14 Joint Left: short The GRB+GW redshift detections distribution are obtained of bywell considering,-localized at eachaligned redshift, short the GRBs GW detection (blue) efficiency from XGIS for NS-NS and mergersSXI and by ETthose (green, 46% of THESEUS short GRBs), the ET+CE network and ET+2 CEs network (magenta and pink, 62% and 73%), respectively. Right: Same detectedas the leftalso panel with where IRT misaligned (25%, indigo) short GRBs [results are also from included the (see MOS, text). credit Including A. misaligned Rocchi]. events Joint not short only increasesGRB+GW the total dete numberctions of are obtainedTHESEUS by considering, short GRBs, but at also each boosts redshift, the fraction the ofGW events detection with a joint efficiency EM+GW for detection, NS-NS leading mergers to 63% by ET for ET,(green, 76% for~46% ET+CE of THESEUS and 83% shortfor ET+2GRBs), CEs. the ET+CE network and ET+2CE network (magenta and pink, ~62% and ~73%), respectively [credit: S. Grimm, M. Branchesi, J. Harms]. Right: same as the left panel where misaligned short GRBs are also included (see text). GW detectors THESEUS+GW detectors aligned short GRB+GW aligned & misaligned Including misaligned eventsplausible not joint only observation increases time the total number detectionsof THESEUS short GRBs, short but GRB+GW also boosts detections the fraction of events2G networkwith a joint EM+GW detection, 3.45 yr leading to ~63% for ET, 76%∼0. 04for ET+CE and 83% for ET+2CE.1.8 ET 1 yr (3.45 yr) 5.6 (19.2) 13 (46) ET+CE 1 yr (3.45 yr) 7.4 (25.7) 16 (55) 2.3.1.2ET+2 CEsAdditional electromagnetic 1 yr (3.45 yr) counterparts of CBCs 8.7 (30.1) 18 (61) BesideTable 1theExpected short numberGRB ofprompt joint prompt and GW+EMafterglow detections emission, of NS-NS other mergers/short EM signals GRBs for are THESEUS expected and differentto be detected GW detectors, with assuming 1 or 3.45 years of joint observations. Number estimates of aligned short GRB+GW detections take into account the redshift distribution THESEUSof THESEUS jointly short GRBs with from GW the MOS,observations and the NS-NS of CBC merger events. detection efficiencyThey have at each not distance/redshift yet been detected as predicted alone for the (i.e., different with GW no shortdetectors, GRB) assuming in association SNR=8. Number with GW estimates emission, of aligned and plus so, misaligned predictions short GRBs+GW are more detections uncertain. take intoHowever, account also these the add maximumitional EMviewing counterparts angle for misaligned are of great short GRB interest detection since at each most distance/redshift of them (seeare textexpected and Figs. to 3, 4).be less collimated with respect to the prompt emission, and as such observable from the more frequent GW events observed from misaligned directions (that is, when the orbital plane is not perpendicular to the line of sight). This can significantly distance (see Figure 4).5 Based on such an estimate, the SEUS will allow us to solve in synergy with the next gener- increase the number of multi-messenger sources detected. These additional EM counterparts are described in unique capabilities of THESEUS offer excellent prospects ation GW interferometers include the following: thefor following detecting and the promptinclude emission extended from emission misaligned and short plateau typically observed in short GRBs, whose origin is stillGRBs matter within of debate. the relatively The smallinformation distance reachcarried of GWby these de- additional signals when jointly detected with GWs are expected to provide fundamental clues on the nature of the– post-mergerHow frequent remnant. is relativistic jet formation in NS-NS tectors. In particular, for NS-NS mergers detected by 2G in- and NS-BH mergers? THESEUS will allow for the de- terferometer network, the GRB 170817A-like prompt emis- tection of at least a few to about 10 or more short GRBs sion would be observable up to 10 − 30 deg, depending on associated with GW-detected NS-NS/NS-BH mergers. the energy band (Figure 4), corresponding to a detection The association of a short GRB with NS-NS/NS-BH merg- rate increased by almost a factor of 50 with respect to the ers unambiguously brought us the proof of the formation result for aligned events only (Table 1). At the typical dis- of a relativistic jet. Along with detections, THESEUS tance reached by a 3G detector such as ET, the prompt emis- will also allow for confident non-detections in case of sion would still be observable by THESEUS up to order face-on mergers without a short GRB (based on the bi- ∼ 10 deg, more than doubling the joint detection rate (Ta- nary system inclination extracted via the GW signal). ble 1). – What is the jet launching mechanism in NS-NS/NS- Building statistically relevant samples of short GRBs for BH mergers? The time delay between the GW merger which coincident GW observations will be available (Ta- epoch and the GRB peak flux is a powerful diagnostic ble 1), which is a unique capability of THESEUS, will allow indicator for the jet launching mechanism (e.g., [12,55, for unprecedented investigations on the nature of compact 56,57]), which is still a matter of debate (e.g., [58,59,60, binary mergers. Fundamental open questions on the nature 61,62]). The significant number of short GRBs observed of CBC sources and short GRB central engines that THE- by THESEUS in synergy with GW detectors will allow us to uniquely characterize this important parameter and 5 We refer here to the GRB 170817A jet angular structure as inferred in [46]. We note that there are also different angular structures compat- highlight differences between NS-NS and NS-BH sys- ible with the observations (e.g., [53]). tems. THESEUS Assessment Study Report page 22
Multi-Messenger Astrophysics with THESEUS in the 2030s 7
– What is the nature of the short GRB central engine The richness of information inferred from and the origin of the still unexplained extra-features GRB 170817A enabled us for the first time (e.g., “Extended Emission”, “Plateaus”)? to quantify how the high-energy prompt For short GRBs detected by THESEUS, the subsequent emission becomes gradually softer and less energetic as the viewing angle increases X-ray emission will be observed via the on-board SXI with respect to the jet axis. From this and/or by communicating the accurate sky localization information, by assuming GRB 170817A- to X-ray telescopes such as Athena. In presence of a co- like events, the maximum viewing angle at incident GW detection, a combined analysis will be pos- which THESEUS could detect the prompt sible, shedding light on the nature of the merger remnant emission depending on distance has been (i.e. accreting BH or massive NS; e.g., [63,64,65,66, estimated. The unique capabilities of THESEUS offer excellent prospects for 62]). This unprecedented collection of information will detecting the prompt emission from also unveil the origin and statistical properties of puz- misaligned short GRBs, in particular in the zling X-ray features like the Extended Emission and the 2-30 keV band (Figure 2-13) where we X-ray plateaus (see Sections 2.1.1, 2.1.2). predict at least 80% more events with – Do jets have a universal structure and are there any respect to the expected number of aligned 3 systematic differences between NS-NS and NS-BH Fig. 4 Maximum distance/redshift for detecting with THESEUS the short GRBs with accurate localizations Figure 2-13 The pink, violet and blue stripes indicate the maximum prompt emission of a short GRB like 170817A versus the viewing an- (i.e. from 41 to 73). The increment of joint mergers? The afterglow properties of short GRBs viewed distance/redshift for detecting with THESEUS/XGIS the prompt gle, depending on the energy band (red, violet, and blue lines/stripes). short GRB+GW detections by including from outside the core of the jet strongly depend on the jet emission of a 170817A-like short GRB as a function of the viewing Calculations are based on [54] and employ a series of simplifying as- misaligned events is shown in Figure 2-14 angle. Dotted horizontal lines indicate the ET and 2G maximum structure (and in particular the energy and Lorentz fac- sumptions. (right panel). It is particularly evident at distance reach for NS-NS mergers, respectively. At 330 Mpc (typical low redshifts where the maximum viewing tor angular distribution around the jet axis). THESEUS 2G distance reach for random inclinations), for instance, THESEUS will detect and localize down to arcmin level several can detect up to a viewing angle of ~20°-40° (2-30 keV band), providing angles at which THESEUS could detect a misaligned short GRBs (Table 1). The afterglow pro- >25-100Besides times the more short detections GRB with prompt respect emission, to a viewing other angle EM within sig- short GRB are larger and where GW interferometers are more sensitive for NS- file of the brightest nearby sources will be monitored nalsthe jet directly core (<4°) related [Credit: to O. short Salafia]. GRBs are expected to be de- NS merger detection. Table 2-3 shows the tected with THESEUS jointly with GW observations of CBC with SXI and IRT (see Section 10). Moreover, synergy expected joint detections for aligned and misaligned short GRBs. with powerful facilities, such as the contemporaneous events. These additional EM counterparts are described in Soon after the main burst, the quickly fading soft X-ray tail interpreted as high-latitude emission from the jet, mission Athena, will allow for deep and long afterglow the following Sections and include the well-known jet after- can be detected with SXI. In addition, the propagation of the GRB jet in the interstellar medium is known to glows as well as the so-called “Extended Emission” and “X- monitoring. produce a multiwavelength afterglow signal, from X-rays to radio, via synchrotron emission at the forward – Do jets have a universal structure and are there any rayshock. Plateaus” By assuming often a observedGRB 170817A-like in short GRB jet, THESEUS events, whose SXI and IRT will be able to catch on-axis X-ray and systematic differences between NS-NS and NS-BH originIR afterglow is still emission matter ofup debate.to z~1-2. Extended Very accurate Emission sky localization and X- from SXI and IRT observations will allow mergers? The afterglow properties of short GRBs viewed rayfacilities Plateaus, such neveras ATHENA, detected ELT, without or SKA, the prompt to deeply short monitor GRB the source and thus to further characterize the from outside the core of the jet strongly depend on the jet emission,following are emission. of particular Moreover, interest this synergyas they (i) will might significantly be sig- improve the chances of identifying the host galaxy and obtain a precise redshift measurement. For misaligned events, afterglow detection will also be structure (and in particular the energy and Lorentz fac- nificantly less collimated with respect to the latter and as possible at small distances. For instance, IRT can detect such emission up to a viewing angle of ~27° for an such observable from a larger fraction of GW events, and tor angular distribution around the jet axis). THESEUS event at ~40 Mpc (i.e. the GW170817 distance) and up to ~8° at ~300 Mpc. Misaligned afterglows also peak will detect and localize down to arcmin level several (ii)at times could that provide can be hours fundamental or days later clues than on the the prompt nature burst, of the in which case actual observations would require misaligned short GRBs (Table 1). The afterglow pro- post-mergera dedicated remnant.re-pointing strategy (see §2.4). THESEUS has unique capabilities to detect and localize a file of the brightest nearby sources will be monitored statistically significant fraction of short GRBs. Together with GW observations, which will probe the nature with SXI and IRT (see Section 10). Moreover, synergy and properties of the merging system and the remnant object, THESEUS will unveil the physics governing 2.1.1 Extended Emission with powerful facilities, such as the contemporaneous GRBs and its implications on relativistic astrophysics (see Table 2-3). mission Athena, will allow for deep and long afterglow A fraction of short GRBs, immediately after the hard spike, monitoring. shows a softer and prolonged emission (“Extended Emis- – What is the role of merging NS-NS and NS-BH sys- 3 sion”,Computed hereafter by boosting EE) the lasting aligned a short few GRBs tens upby a to factor hundreds (1-cos ofview(z))/(1-cos jet), where jet ~4° is the jet core half- tems in the chemical enrichment of the Universe? Kilo- secondsopening angle [67]. (conservative Past attempts choice to quantifyfrom [57])the and fractionview (z) is of the short maximum detection angle at each redshift according to nova observations provide crucial information on the r- the results in Figure 2-13. GRB with EE led to a wide range of values that goes from process element formation accompanying these events, 2% up to 25%, depending also on the sensitivity band of the which is a fundamental open problem. Moreover, the gamma-ray detector used for the classification [68,69,70]. overall contribution to the r-process element abundances A recent systematic analysis of Swift XRT and BAT data of relative to the one from supernovae (SNe) remains un- a sample of 65 short GRBs (6 times larger than past studies, clear. THESEUS accurate sky localization of several NS- [71] suggests the presence of a severe bias against the lack NS/NS-BH mergers will allow for kilonova detection of an X-ray view of the prompt emission, with a true fraction and characterization through the follow-up with the on- of short GRBs accompanied by EE of more than 75%. board NIR telescope and/or through ground-based follow- A prototype of short GRBs with EE is GRB 050724 at up campaigns (see Section 11). z = 0.26 (Figure 5). Simulations of this burst show that THESEUS could have clearly detected both the main hard P GRB EE 2% 25%, - P ( N , G & 2 0 1 G0R, B E E . 2 0 1 3 , K . , 2 0 1 5 , L ,. 20 1 6 ) . 2%A 2 5 % , R B A - 6 5 G R B (6 (N , G &, K 2 0 1 0. , 2B0 1 7 ) . 2 0 1 3 , K . , 2 0 1 5 , L , . 2 0 1 6 ) . A - , R B A G R 6B5 G R B ( 6 , K . 2017) EE 75%. - , GRB EE 75%. EE . EE ( . . 10-100 ) B H - EE N . E E ( . . 1 0 -1 0 0 ) B H - ( . . B . 2 0N1 1 , M . 2 0 1 2) . I , EE ( . . B . 2 0 1 1 , M . 2 0 1 2 ).. FI , EEEE G R B - N - N . F . I -E E ( 0 . 3 - 1 0 ) E E G R B - 1 0 4 7 1 0 5 0 / . N - N . I -G R B ( 0 .3 - 1 0 E E ) GRB 47 50 05 0 7 2E4E = 0 .2 6 ( F 2 . 4 . 1. 11-01 ). 1 0 / . HGRE BE E E G R B 0 5 0 7 2 4 = 0 . 2 6 (F 2 .4 . 1 .1 - 1 ) . E E HGEI E . F E E 8 G R B G I E E ( K . 2 0 1 5 ) . F E E 8 2 G R B E E ( K . 2015) EE 2 EE GI . EE GI . 8 Riccardo Ciolfi et al.
Fig. 5 Left: Prototype of short GRB with Extended Emission (EE), GRB 050724 at z=0.257, detected with Swift/BAT [72]. [Figure produced via the Swift Burst Analyser [73]] Right: Simulations of the 2−30 keV spectrum of GRB 050724 obtained with XGIS (assuming 15 deg off-axis F . 2.4.1.1-detector1 L calibration), a : where the main hard spike (black) G andRB EE (red) areE detected at 35E sigma with 3 s( ofEE exposure), GR andB 0 22507 sigma24 with a 100 =0. s of257, F . 2 S.4 .1 . 1/B-1Aexposure, TL ( B a respectively. a : 2 0 0 7 ) . R a : G Ra B E 2 -3 0 VE ( E GER),B G 0R507B 2045 07 b 2a4 a = 0. 2X57GI,S ( a S /B 1A5T ( B -aa a b a2 0 0 7 ) . R ) , a : a a ( b a 2 -) 3a0 EVE ( ) a G R B a 0 53507 2 4 ab a 3 XGIS (a a1 5 spike 2 2 - and a the a EEa componentb 1 a0 0 with ) XGIS, , as well as charac- a . a 2.1.2 X-ray (b plateaus a ) a EE ( ) a a 35 a 3 a terized22 its spectrum.a 1 Further00 simulations over , a sample of 8 . short GRBs with EE at known redshift [70] show that EE The soft X-ray afterglow lightcurve of GRBs is often charac- can be detected up to z ' 2 and in some E casesE the detection terized by an initial steep decay,HE followed E by a rather shallow significance of the EE component with XGIS is even higher decay phase (so-called “plateau” phase) which can extend than the detection significance of theG main E hard E spike. up to several thousands . F of seconds. 2 .H4.1E According. 1-E2 to over 15 E E H E E G years of observations by . Swift, ,F . a., large 2 fraction. E4. 1 .G1 of- 2 all short . GRBs (≈50%) may be accompanied by an X-ray plateau. A E E H E E common , interpretation for the X-ray , plateaus. . , is based E G on GR an B E E . E E . F , external shock , emission sustained G R by B energy injection E E from 5 0 % G R B EE EE - The physical interpretation 4 of the EE is still unclear. The an active central ( engine that can either be an accreting15 -20 BH EElong EE duration (order .10 F− 100 s) challenges , the lead- or a highly magnetized NS (see also SectionGRB 2.2.1). In E theE 50% E E - ing 4 scenario -5 ) , envisaging H E 4E an accreting BH as the 5 short 0 - 1 GRB 0 0 EE latter case,3 . 4 5 the plateau , emission( can be poorly collimated 1 5 or 8-2 0 - GRBcentral engine and supports the formation of a long-lived even nearly isotropic E (e.g., ( [75,76]). According 2.4.1 to-1 an). alter- spinning4 -5 down), massiveHE E NS remnant (e.g., [74]; see also50- Fig-100 nativeEE interpretation, 3.45 both , the steep decay and the plateau 8 - ure 6). In this alternative scenario, the EE is expected to be are instead due to high-latitude emission (HLE) produced GRB much less collimated with respect to the main spike. For this from a structured jet whose E energy ( and bulk Lorentz 2.4.1 fac--1). reason, the EE can also represent a possible “short GRB- tor gradually decrease with the angular distance from the jet symmetry axis (e.g., [77,78]). This model predicts an X-ray less” EM counterpart of NS-NS mergers, which can in turn further boost the number of EM counterparts of GW sources emission that becomes fainter at larger polar angles and thus that THESEUS will be able to catch. As an illustrative exam- detectable, for a given distance, up to a maximum angle (see ple, Figure 7 shows the expected number of EE signals that Figure 9). THESEUS can detect in 1 year in combination with ET GW FigureF 8 shows 2.4.1 the.1 X-ray-2 T flux range spanned by the best b detections. This number depends on the two still uncertain observedEE plateaus associated ( with (aligned) ) short GRBs with a a parameters, namely the fraction of short GRBs with EE and redshift measurements, ET GW where the latter allows a to a rescale thea - NS-NS the characteristic opening angle of the EE. For instance, by flux itself F with , distance. a 2a.4 .1 A .1 comparison- 2 T with the a sensitivity G R B b assuming a fraction of short GRBs with EE of 50% and an of the THESEUSEE SXI shows that( such an instrument ) is per- a a EE half-opening angle four times larger than the main hard fectly suitable to catch this emission and, assuming an expo- spike (assuming a jet half-opening angle of a few degrees, sure of 1 ks, would ET allow GW us to detect about 90% (30%) a of alla a - NS-NS this would correspond to 10−15 deg), THESEUS would de- X-ray plateaus up to 330, a Mpc a (2.9 Gpc), which is the typical a GRB tect about 45 EE signals with a GW counterpart observed by 2G (ET) GW detection distance for a randomly oriented NS- ET. The largest fraction of these events will be “short GRB- NS merger. For GRB 170817A, the X-ray plateau lightcurve less”, thus adding to the overall number of multi-messenger predicted by the HLE modelling is consistent with the non- detections enabled by THESEUS. detection by, e.g., Swift and MAXI. At the same time, the THESEUS Assessment Study Report page 26
possible inclinations. In the case of a magnetar origin, plateaus might be detected by THESEUS as “short GRB- less” X-ray transient sources, with lifetime of the order of ~1-10 ks up to 1 day and with ~10s-1ks temporal delay with respect to a spatially consistent GW event from a NS-NS/NS-BH source. The 0.5 sr SXI field of view contains typical sky-localizations of signals detected by at least 2 GW interferometers ( [70], [71]). Based on Swift/XRT X-ray plateau observations with known redshift, it can be inferred that about 90% and 30% of these plateaus can be detectedTHESEUS with THESEUS/SXI EE detections with 1 ks in of 1 exposu year withre coincident within z=0.7 (ET) in 3.45 yrs within the 2G and the ET GW distance reach for NS-NS mergers, respectively. In the case of a HLE origin, a misaligned event observed with SXI will yield a steep X-ray decay transient with peak time ranging from a few 100 s up to >1 ks depending on the viewing angle, with a phenomenology similar to long GRBs (see §2.4). Joint detections of THESEUS and 3G GW detectors (able to detect the post-merger signal from the remnant) willMulti-Messenger unveil the Astrophysics connection with among THESEUS NS in themergers 2030s and new-born magnetars and all the associated EM signature9 s.
2.3.1.2.3 Spin-Down Powered Transients In the case a NS-NS merger produces a long-lived millisecond magnetar, nearly isotropic soft X-ray to optical transients with timescales of minutes to days can be powered by the magnetar EM spin-down emission. THESEUS/SXI can detect such transients up to redshift z~1.3 A potentially powerful nearly-isotropic emission is expected if a NS-NS merger produces a long-lived fraction of SGRB with EE millisecond magnetar, i.e. a remnant object that does fraction of SGRB with EE not collapse to a BH for as long as minutes, hours, or more (see Figure 2-16). Soft X-ray to optical transients Fig. 6 Schematic cartoon depicting the possible remnant formation can beopening powered angle ratio by theEE-to-prompt magnetar short EM GRB spin-down Figurechannels of2-16 NS-NS Cartoon and NS-BH on mergers. the NS-NS/NS-BH [From [50]]. possible emission reprocessed by the baryon-polluted opening angle ratio EE-to-prompt short GRB remnant formation channels (from Ascenzi et al. 2020). environmentFig. 7 Number of surrounding EE signals that THESEUSthe merger can detectsite ( in [86], 1 year [83 in ]). combination with ET GW detections, depending on the fraction of sensitivity of THESEUS/SXI, combined with the ability of Inshort soft GRBs X-rays, accompanied such by EE spin-down and on the ratio powered between the transients char- 46 48 (SDPTs)THESEUS can to trigger last for the a burst timescale and rapidly of minutes localize it, to would days andacteristic their openingexpected angle luminosities of the EE and that are of theup short to 10 GRB–10 jet core. erg/s [83],have allowedwhich forwould an early be reachable and confident by detection.SXI up to 0.9-9 Gpc with 1ks exposure. OneSo or far, more it has unambiguous not been possible detections to disentangle of this the type dif- of emissionwith IRT after up to a' NS-NS20 deg, withmerger peak would emission indicate time around that the remnantferent interpretations is long-lived, of X-ray allowing plateaus us outlinedto achieve above signi (andficant2 days.constraints Going toon a the larger NS distance equation of 500of state Mpc and (nearly other the key propertiesothers; e.g., of [79,80], the remnant as the predicted itself ( flux[87], evolution [88]). Mor can ineover,maximum it would distance provide reach crucial of 2G information GW detectors to foresti NS-NSmate the any case fairly well reproduce the events observed with currently unknown fraction of mergers forming a long-livedmergers), NS SXIremnant. and IRT Finally, could detectit would a GRB clarify 170817A-like the possible Swift/XRT (e.g., [81,82,83,77]). THESEUS will give us the afterglow signal respectively up to '4.5 deg and '10 deg. connectionopportunity to with collect the a statistically extended significant emission sample and/or of the X-ray plateaus of short GRBs. In the case of GW170817/GRBplateau detections in synergy170817A, with no GW evidence observations for a and SDPT thus was found in the soft X-ray band. However, the first deep pointedto constrain observations the emission at model ~keV (possibly photon aided energies by the only iden- started as late as ~15 h after merger with Swift/XRT [89], 2.2 Other CBC counterparts of interest for THESEUS-9 2 andtification the earlier of the remnant constraints nature, provided i.e. BH vs. by NS, MAXI via the 4.6 post- h after merger with a flux limit of ~8.6 10 erg/cm /s [90] weremerger not GW able signal). to exclude In this respect, a SDPT. also The the numbercombination of “or- of the THESEUS/SXI sensitivity at ~keV energies and its 2.2.1 Spin Down Powered Transients fieldphan” of X-ray view plateaus about detected104 times (i.e. larger without than a prompt Swift/XRT short will offer much better prospects for a detection within GRB detection) will be revealing. minutes/hours after a GW trigger. A potentially powerful nearly-isotropic emission is expected if a NS-NS merger produces a long-lived highly magnetized 2.3.1.2.42.1.3 Jet afterglows Kilonovae with SXI and IRT NS that does not collapse to a BH for as long as minutes, THESEUS/IRT can detect the kilonova emission associhours,ated or more with (see nearby Figure 6). short Soft X-ray GRBs to detected optical tran- with XGIS/SXI,The propagation ensuring of a GRB the jetbinary in the merger interstellar sky medium localizatisientson down can be to powered the arcsecond by the NS EMlevel. spin-down This will emission allow re- next processed by the baryon-polluted environment surrounding generationis known to produce powerful a multi-wavelength telescopes, such afterglow as the signal, ELT, to take high-detected-quality spectra and extract from X-rays to radio, via synchrotron emission at the for- the merger site (e.g., [89,90,91,75,76]), which consists of chemical abundance information, ultimately defining the role of NS-NS/NS-BH mergers in the cosmic ward shock [84,85]. GRB 170817A was the first short GRB a dense cloud of material expelled in the early post-merger enrichmentviewed with line of r-process of sight significantly elements. misaligned with re- phase (e.g., [92]). In soft X-rays, such spin-down powered spect to the jet axis and the properties of the observed after- transients (SDPTs) can last for a timescale of minutes to glow radiation offered a unique chance to probe the angular days and their expected luminosities are up to 1046−1048 erg/s jet profile. Taking this event as a reference, we can estimate [75,76], which would be reachable by SXI up to 0.9−9 Gpc
the maximum distance at which the afterglow signal is above with 1ks exposures. the detection sensitivity for the IRT and SXI instruments on- One or more unambiguous detections of this type of emis- board THESEUS, depending on the viewing angle with re- sion after a NS-NS merger would indicate that the remnant is spect to the jet propagation axis. In Figure 10, we show the long-lived, allowing us to achieve significant constraints on result based on the power-law angular jet structure that best the NS equation of state and other key properties of the rem- fits the observations according to [46,86] (see also [87,88, nant itself (e.g., [93]). Moreover, it would provide crucial 54]). A GRB 170817A-like afterglow signal at 40 Mpc could information to estimate the currently unknown fraction of be detected with SXI up to an inclination of ' 10 deg, with mergers forming a long-lived NS remnant. Finally, it would a peak emission time between a few hours and 1 day, and clarify the possible connection with the extended emission i h e e ded e i i a d f he e i g a gle a i be ee EE a d e i i [C edi : R. Ci lfi]. 2.4.1.2 C ib i f X- a la ea The f X a af e g igh c e f GRB i f e cha ac e i ed b a i i ia ee deca , f ed b a a he ha deca ha e ( -ca ed a ea ha e) hich ca e e d e e a h a d f ec d . Acc di g e 15 ea f b e a i b S if , a a ge f ac i f a h GRB ( 50%) a be acc a ied b a X- a a ea . Fig e 2.4.1.2-1 h he X- a f a ge a ed b he be b e ed a ea a cia ed i h h GRB i h ed hif ea e e , he e he a e a e ca e he f i e f i h di a ce. A c a i i h he e i i i f he THESEUS SXI h ha ch a i e i e fec i ab e ca ch hi e i i a d d a de ec ab 90% (30%) f a X- a a ea he ica 2G (3G-ET) GW de ec di a ce each f a a d ie ed NS-NS e ge (a i g a e e f 1 a d ha he b f NS-NS e ge i ea b he di a ce each). 10 Riccardo Ciolfi et al.
101 THESEUS-SXI Limit 1 ks 4 THESEUS-SXI Limit, 100 s 10 2 Jet Core c z = 0.0099 (GW 170817A)
) z = 0.045 (LVC BNS range)
2 3 5 m 10 Fig e 2.4.1.2-1: E ec edz =fl 0.5 (ET a BNS ge range) f h GRB c / ) s s / X- a la ea c ed f a elec ed a le f ( g k r a e 8 S if /XRT e e i h k ed hif a d e ca2lede ( 10 p
t x g
u a diffe e di a ce . Ve ical li e i dica e he l o F L
k 10 11 di a ce hich a a d l ie ed BNS a 1 e
P e ge ca be de ec ed i h 2G e k a d ET.
10 14 [C edi : G. Oga e a ] 0 10 17 0 10 20 30 40 50 60 70 Viewing Angle (deg) Fig. 8 Expected flux range of X-ray plateaus associated with (aligned) Fig. 9 short GRBs as computed from a selected sample of Swift/XRT events Predicted HLE peak fluxes at different viewing angles com- A withc known redshift i e and e rescaleda i atf different he X distances.- a Vertical a ea lines i bapared ed with a THESEUS/SXI e e a sensitivityh c e withi i 100 s and a 1i ks e expo-d b sures (horizontal red dashed and solid lines, respectively), for a e eindicate g i the ec typical i distancef a at whichac i ae randomlyce a oriented e gi NS-NSe ha ca ei he be a acc e i g b ac h e a i i g merger can be detected with 2G network (330 Mpc) or ET (2.9 Gpc). GRB 170817A-like event placed at three different distances (circle, di- d ag e a ( ee a 2.4.1.3). I hi ca e, he amond,a ea ande crossi i markers). ca Color-coded be is thec peak i time.a ed Calculations e e are based on [77,78] (see [78] for a similar figure referred to a different ea i ic (e.g., Siege a d Ci fi 2016a,b). Accevent). di g a a e a i e i e e a i , b h he and/or the X-ray plateaus of short GRBs. In the case of eGW170817/GRBe deca a d 170817A, he a no ea evidence a e i for e aa SDPTd d e was high- a i de e i i (HLE) d ced f a foundc e ind the e soft h X-ray e band.e e g However, a d b the first L deep e pointed fac g Duringad a the d nextec e decade,a e i weh h maye a observeg a d otheri a kilonovaece f heobservations e ate ∼ keV a i photon (e.g energies., Oga onlye a started e a as . late 202 as0, Bassociatede ia i i with e a nearby . 202 NS-NS0, A c ande perhapsi e a . NS-BH2020). merg- Thi ∼de15 h afteredic merger a X with- a Swift/XRT e i i [94], ha and bec the earliere fai eers a as a well ge as kilonovae a a g without e a d GW h counterparts. de ec ab Then,e, f in a gi constraintse di a providedce, by MAXI a a 4.6 i h after mergera g e with( ee a fluxFig ethe 2. 2030s,4.1.2- the2, IRTef onboard a e ). THESEUS F GRB will 17 also081 contribute7A, he limit of 8.6×10−9 erg/(cm2 s) [95] were not able to exclude to the search and localization of kilonova signals, in par- X-a a SDPT. a Theea combination igh c e of the ed THESEUS/SXIic ed b he H sensitivityLE de ticular i g i if c associated i e with i ah detectable he - alignedde ec i or misaligned b , e.g., S atif keV a energiesd MAX andI. itsA field he of a view e about i e, 10 h4 etimes e largeri i i shortf TH GRB.ESE AsUS shown/SXI, in c Figure bi 11,ed the i IRTh h cane a detectbi i the f THthanESE Swift/XRTUS willigge offer h muche b better a prospectsd a id for a detec-ca i e i ,full SED d (Spectralha e a Energy ed Distribution)f a ea of a a d kilonova c fid likee de tionec i within ( e minutes/hourse Fig e 2.4 after.1.2 a-2 GW, i trigger.gh a e ). AT2017gfo up to 320 Mpc (180 Mpc) with 600 s (60 s) of exposure, within one day from the merger epoch. At later 2.2.2 Kilonovae with IRT times, the kilonova will be fading away, but IRT will still be capable to detect the source in each filter thus allowing Neutron-rich matter released from NS-NS/NS-BH mergers to build spectral energy distribution up to 180 Mpc within a undergoes rapid neutron capture (r-process) nucleosynthe- few days after the trigger. For nearby sources (< 40 Mpc), sis, leading to the formation of very heavy elements such as near-IR spectra can also be obtained. gold and platinum. This scenario likely provides a signifi- cant (if not dominant, compared to SNe) contribution to the observed abundances of rare heavy elements in the Universe. 2.3 CBC redshifts and prospects for H measurement Radioactive decay of the newly-formed and unstable nuclei 0 powers a rapidly evolving, nearly isotropic thermal transient In the last years, two main measurements of the Hubble con- known as a kilonova, the observation of which not only wit- stant H , obtained from Planck observations of the CMB nesses cosmic heavy element production, but can also probe 0 and from the SNIa distance ladder, have come into signifi- the physical conditions during and after the merger phase cant tension with a steadily growing discrepancy, currently (e.g., [96]). at more than 4 sigma level (e.g., [104]). An independent, The first robust observation of a kilonova, following a new measurement of H would be of utmost importance in few candidates (e.g., [48,97], was the optical and infrared 0 order to understand if the current discrepancy is due to pos- counterpart of GW170817 (e.g., [98,99,100,101,102]; see sible systematics or is the sign of a cosmological crisis that also [96] and refs. therein), named AT2017gfo, discovered requires new paradigms. The luminosity distance from the about 11 hours after the GW/GRB trigger via galaxy target- detection of GWs from CBCs and the measurement of their ing inside the GW plausible sky area ([13] and refs. therein).6 redshift through their EM counterpart has already proven to 6 After AT2017gfo, the re-analysis of different events led to the be a potential alternative probe for H0 with the example case identification of other likely kilonovae (e.g., [103]). of GW170817 [105]. Multi-Messenger Astrophysics with THESEUS in the 2030s 11
Fig. 10 Maximum redshift/distance vs. inclination for a THESEUS detection in the H-band (circles) and at 1 keV (X-rays) with IRT and SXI, re- spectively, for jet afterglow radiation assuming the GRB 170817A power-law jet structure from [46,86]. Color-coded is the peak time. Calculations are based on [87,88]. Fig e 2.4.1.4-1 Lef a e : ea νFν c he i c i a i ed hif ( i i di a ce) a e, a 1 eV f To solve the current tension, however, a precision level to perform successful ground-based afterglow follow-up, we he GRB 170817A e - a e c e f ofG thehi order a ofda 1% e must a be. ( reached.2019) In, thisc context, THE-ed i generatedh he 7 1000 de optical de aligned c ib anded misalignedi Sa a afterglowfia e a . SEUS observations of a large number of short GRBs in syn- synthetic light curves assuming GRBs with equivalent isotropic (2019). The e i i i f SXI f a 10 e ergy with e 3G i interferometers h representa a ad uniquea he opportunity.d ed i radiatede. [C energy edi >: 10O50.erg S anda a meanfia] value R'i2g×h 10 51 aerg e : i c i a i a i ed hif /di a ce f a TSimulationsHESEU ofS NS-NS de e mergersc i observed i he with H the-ba 3G d net- (ci andc e then ) a compared d a with1 theeV magnitude (X- a limits ) ( of differenti h IRT work along with an instrument like THESEUS/XGIS have telescopes that may operate in the era of THESEUS (in par- a d SXI, e ec i e ). The ea i e f he af e gbeen performed i i bydi [106].ca e Theird i resultsa he predict c a number f of heticular, i we considered. [C ed herei : LSST/VRO,G. La theb] Liverpool Tele- joint detections of 130 − 300 in 10 years, from which H0 scope, and GTC/OSIRIS). Results show that, for short GRBs could be measured with a precision of 0.2 − 0.4% by as- observed with viewing angle between 0 and 10 degrees with 2.4.1.5 C ib i f kil ae i hsuming IRT that a redshift can be measured for all events via respect to the jet axis and with no IRT detection, ' 50% either optical or X-ray spectroscopy: with this assumption, will have a detectable optical afterglow (that unambiguously Ne - ich a e e ea ed f NS-NFigureS√/N 12S shows-B that,H by rescalinge ge these precision de levels g as apinpoints id thee host galaxy) c bya providing e a ground-based( - c tele-e ) 1/ N, the goal of ∆H0/H0 ∼ 1% can be reached with scope follow-up reaction time of a few hours. With the same c e he i , eadi g he f a i N ' 15 eventsf jointlye observed hea with thee 3G e network e cassumptions,h a g' 13% dof a short d GRB observeda i with viewing. Thi (ET+2 CEs) and N ' 25 events jointly observed with ET angle between 10 and 30 degrees with respect to the jet axis ce a i i e ide a ig ifica (ionlyf (the lower d number i ofa events ) providingc ∆H ib0/H 0 ∼i 1% will have he a detected b e optical e afterglow.d ab By d takinga intoce ac- f with the ET+2 CEs network with respect to ET only is due count these results, H0 should be measured with ∼ 1% ac- a e hea e e e i he U i e e. Rto thead betteri a parameterc i e estimation deca with the formerf h network).e e curacy -f (at 1 sigma)ed with a 1 yrd of synergy withab the e ET+2 CEsc ei THESEUS can reach these detection numbers in 1-2 years network and 3.45 yr with ET (Figure 12). e a a id e i g, ea i of operationsic he in synergy a with a 3G GW ie detectors (see Tab. 1). a a i a , he b e a i However, as we learned from past observations, the red- f hich i e e c ic heshifta cannot e be e measured e for all short d GRBs c duei to , host b 3 Otherca GW a sources be he h ica galaxy identification challenges. This will likely not affect c di i d i g a d af e he e ge hthea' e25% (eof.g THESEUS., Me short g GRBse 2 detected020 with). IRT 3.1 Core-collapse of massive stars since their sky localization to arcsec accuracy will enable unambiguous identification of the host galaxy and redshift Beside CBCs, core-collapse supernovae (CCSNe) represent S fa , he b b e a i f ameasurement i (in thea vast, a majority ofg cases). a Forfe the remain- heanother ca type d ofid GWa e sources (e that.g are. T ofa great interesti e for a . ing ' 75% without IRT detection, the large number of galax- the astrophysics community. However, contrary to the CBC 2013, Ji e a . 2015), a he ica iesa containedd i f in thea XGISed orc SXI error e boxes a for almost f all GW170817, a ed AT2017gf , 7 short GRBs (i.e. at distances >50−100 Mpc) severely chal- Using the python module afterglowpy [107] that however does not di c e ed ab 11 h af e he GW/GRB igge ia ga a a ge i takeg intoi account ide possible h “rebrightenings”e GW observed a in severalib e optical lenges the identification of the host galaxy if no transient op- afterglows, the origin of which is not yet fully understood (e.g., [103]). tical afterglow is detected. In order to quantify the chances Therefore, provided estimates are conservative. a ea (e.g., Pia e a . 2017). D i g he e decade, e a b e e he i ae a cia ed i h ea b NS-NS a d e ha NS-BH e ge a e a i ae i h a GW c e a a d a i a e i be a ed b he Ve a R bi Ob e a (e.g., A d e i e a . 2019). The , i he 2030 , a e c ib i he ea ch a d ca i a i f i a ig a , e ecia if a cia ed i h a de ec ab e - ff-a i h GRB, i be gi e b he IRT b a d THESEUS. A h i Fig e 2.4.1.5-1, IRT ca de ec a i a i e AT2017gf 325 M c (180 M c) i he i-ba d i h 600 (60 ) f e e, i hi e da f he e ge e ch. F SED (S ec a E e g Di ib i ) ca be b ai ed 180 M c i hi a fe da af e he igge . High e i ec a (H<17.5, 1800 ) ca be b ai ed f he ea b ce (i.e. <40 M c). Gi e -3 -1 he c e e i a e f NS-NS e ge a e de i [110-2810] G c (Abb e a . 2020) a d a i g ha he e e ge a e a acc a ied b a AT2017gf - i e i a, e e i a e 6-60 i ae e ea de ec ab e b THESEUS/IRT 180 M c i h 60 f e e. I c ea i g he e e 600 , a AT2017gf - i e i a d be de ec ab e f a a NS-NS e ge i hi he di a ce each f he 2G+ GW e . Wi h i f he faci i ie , IRT d be ab e fi d he i a i hi he <15 -7 -2 i e e b f XGIS a d SXI. A e a i e , f gi e ca i , i ca be ed i he i a e i a d ib e ac ec a i f a i , i a e c ib i g be e defi i g he e f NS-NS a d NS-BH e ge i he c ic e ich e f hea e e e ( ee Sec i 2.4.4). THESEUS Assessment Study Report page 27
12 Riccardo Ciolfi et al. Neutron-rich matter released from NS-NS/NS- BHbe mergers observable undergo up to a rapid certain neutron viewing capture angle (r- with respect process)to the GRB nucleosynthesis, jet axis, via the prompt leading and afterglowto the emission formationand possibly of very also viaheavy the extendedelements emission such as and/orgold an X-ray andplateau. platinum. Low LuminosityRadioactive GRBs decay (LLGRBs; of the newly- e.g., [120,121]) formedand X-ray and Flashes unstable (XRFs; heavy e.g., nuclei [122]) populating powers a the nearby rapidlyUniverse, evolving, if associated nearly with isotropic CCSNe8 detectable thermal in GWs, transientare also very known promising as a as they ‘’kilonova’’, are expected the to be more observationnumerous thanof which ordinary not longonly GRBswitnesses and cosmic their softer emis- nucleosynthesission makes them of idealheavy targets elements, for THESEUS.but can also In addition, probefor those the physical CCSNe giving conditions birth during to highly and magnetized after NSs, theSDPTs merger observable phase [92]. by THESEUS/SXI So far, the only may robust be produced (as observationfor the highly of magnetized a kilonova, NS among remnants a few resulting other from NS- Fig. 11 Multi-band light curves of the kilonova AT2017gfo (from candidatesNS mergers; [93], see Section was the 2.2.1). optical Finally, and shock infrared breakout sig- Figure[108]) compared2-17 Multi-band with THESEUS/IRT light curves sensitivity.of the kilonova THESEUS AT2017gfo can de- [91] compared with THESEUS/IRT sensitivity. THESEUS can counterpartnals associated of GW170817, with SNIbc andnamed SNII AT2017gfo explosions are( expected tect a kilonova like AT2017gfo with 5 sigma up to 320 Mpc in all bands [94], [95], [96], [97]). With an exposure of ~150 detectwith 600 a kilonova s exposure, like within AT2017gfo1−2 days with from 5 the sigma merger up epoch. to 320 Near-IR Mpc to follow closely the core-collapse (within ∼10−1000 s), ap- inspectra all bands (H < 17with.5, 1800600s s) of can exposure, be obtained within for the 1-2 most days nearby from sources the s,pearing an AT2017gfo-like as bright X-ray bursts kilonova lasting would for seconds be to tens of merger(i.e. <40 epoch.Mpc). Near-IR spectra (H<17.5, 1800 s) can be detectableminutes and by having THESEUS/IRT luminosities in for the rangea NS-NS1043− 1046 erg/s obtained for the most nearby sources (i.e. <40 Mpc). merger(e.g., [124]).up to ~200 THESEUS/SXI Mpc away and (Figure XGIS 2-17). can detect such shock breakout signals up to about 50 Mpc, leading to an estimated case, their expected GW emission is highly uncertain as it 2.3.1.3rate of the orderCBC ofredshifts one event and per year.prospects for strongly depends on the rather unknown SN explosion mech- H measurement anism (e.g., [109,110,111,112]). While this makes it diffi- 0 Another particular class of GRBs potentially associated cult to predict the GW signal and its detectability, it repre- THESEUS,with CCSNe in and synergy their GW with emission GW detectors are the so and called “ultra- sents a unique opportunity to probe the CCSN inner dynam- ground-basedlong GRBs”, havingEM observatories, a prompt emission will allow lasting us for tens of ics, inaccessible to EM observations. Promising GW sig- tominutes build up up to a several large hours sample (e.g., of [125]). CBCs So far, with only a small nals associated with CCSNe may also originate from the measuredfraction ( ∼ redshift.1%) of GRBs Combining have been the identified redshifts as ultra-long newly-formed compact object soon after birth, in particular withGRBs, the whichluminosity could bedistances due to an measured intrinsic lowfrom rate but also if the latter is a “millisecond” NS (i.e. a NS spinning with theto GW their waveform lower luminosity will lead (see to also an [126]). independent A larger accreting millisecond period) (e.g., [113,114,115,116,117]). The ex- measurementmass with respect of the to Hubble ordinary constant long GRBs with has the been invoked pected event rates in this case depend on the fraction of mil- levelto explain of precision the exceptional required durations, to resolve suggesting the blue super- lisecond NSs that are born in CCSNe (e.g., [114,118]). Dur- currentgiants astension. well as Pop III stars as possible progenitors (e.g., [127]). Another possible explanation is the long-lasting en- ing the 2G GW network era, one may expect GW detections Independent measurements of the Hubble Figure 2-18 Hubble constant 1 sigma precision level as a ergy injection from a newly-born rapidly spinning NS. Also of CCSNe events to be limited within maximum distances constant H are of utmost importance in order to function of the number of compact binary mergers for which the 0 that vary, depending on models, from tens of kpc up to a in this case, if a GW signal is detected from such systems, redshift and the luminosity distance can be measured from the understand if the current tension [98] is due to few Mpc (e.g., [9] and refs. therein; see also [119]). 3G de- possiblethe combination systematics with EM or observations is the sign will represent of a a unique electromagnetic and gravitational wave emission, respectively. opportunity to identify the correct physical scenario. On the In tectors,this plot, with the electromagnetic their ∼ 10 times counterpart larger sensitivity, comes from will aligned lead to cosmological crisis that requires new paradigms. anda correspondingmisaligned short extension GRBs (see of thelast expected column horizonof Table and2-3) open for Thebasis detection of ultra-long of GRB GWs average from properties CBCs and (see, the e.g., [128]), whichnew redshift prospects can for be discoveries.measured. These numbers are conservative measurementsimulation results of their show redshiftthat THESEUS/XGIS through their will be able estimatesThe detection from afterglow of the GW simulations signal from performed a CCSN and/or with electromagneticto detect these transients counterparts up to has an average already distance been of about “afterglowpy” (see text). z ∼ 1 and with THESEUS/SXI up to very large distances a newly-born millisecond NS along with EM counterparts proven to be a new probe for H0 in the case of would represent a breakthrough discovery for NS physics. GW170817(z ∼ 3 or more). [99]. To At solve the expected the current (much tension, smaller) a distances precisionThe most level relevant at least EM of signals the order expected of ~1% in association should be with reachedfor and a jointa large GW number detection, of CBCs THESEUS with measure will thusd be able to redshiftsuch events are needed. are those In temporallythis context, coincident THESEUS or nearlyobservations coin- of catcha large ultra-long number GRBsof short even GRBs for rather in synergy large viewingwith angles. 3Gcident interferometers with the GW represents burst epoch, a unique since theiropportunity. detection Simulations can of NS-NS mergers observed with the 3G networkmark with along more with precision an instrument the start like time THESEUS/XGIS of the GW emis- have been performed by [100]. Their results predict a numbersion and of thisjoint would detections prove of extremely ~130-300 helpful, in ten ifyears not, crucial, from which H0 can be measured with a precision of 0.2% - 0.4% by assuming that a redshift can be measured for all events3.2 via Magnetars either optical or X-ray spectroscopy: with for the challenging signal search process. Such EM signals this assumption, Figure 2-18 shows that, by rescaling these precision levels as , the goal of H /H ~1% are primarily high-energy transients and THESEUS will be A different source of high-frequency GWs0/ can0 originate from can be reached with N~15 events jointly observed with the 3G network (ET+CE+CE) and N~25 events jointly perfectly suited to catch them. the bursting activity of highly magnetised isolated NSs or In particular, long GRBs are known to be associated with magnetars, which are known to manifest themselves as soft highly energetic CCSNe, and therefore nearby long GRBs gamma repeaters (SGRs) or anomalous X-ray pulsars (AXPs) may have a detectable GW counterpart. In this case, the full (e.g., [129,130]). Such bursting activity is likely associated power of THESEUS as a GRB detector can be exploited. Similarly to short GRBs (Section 2.1), nearby events will 8 See, e.g., [123] for an alternative interpretation of XRFs. Multi-Messenger Astrophysics with THESEUS in the 2030s 13
Belgacem+2019 (ET,10yr) High Energy Cosmic Rays (UHECRs) as well. Hence, it is Belgacem+2019 (ET+2CE,10yr) THESEUS+ET (1-3.45yr): 9.8-33.8 SGRBs+GW with z of paramount importance to address the question of the ori- 4 THESEUS+ET+2CE (1-3.45yr): 12.9-40.7 SGRBs+GW with z gin of the high-energy neutrinos, as they can probe the most N 1/2
) Planck
% extreme accelerators in the Universe. \
( SNIa
n 3 o
i Within our Galaxy, no sources are known to date that s i c e
r can achieve EeV energies, except for the cosmic rays pos- p 2
1 sibly interacting with dense proton targets in the Galactic
0
H disk. However, these are likely not the major contributors 1 of the diffuse neutrino flux observed [143]. On the other hand, many classes of extra-galactic sources are considered 0 plausible candidates, as their energetics can explain neutrino 0 1 2 10 10 10 observations (e.g., [144]). Among these, particularly rele- Number of short GRB with measured redshift vant are GRBs, AGNs, and star forming galaxies, which Fig. 12 Hubble constant 1 sigma precision level as a function of the represent targets for THESEUS. The joint detection of a number of compact binary mergers for which the redshift and the lu- large number of neutrino and EM emission sources, feasi- minosity distance can be measured from the electromagnetic and grav- itational wave emission, respectively. In this plot, the electromagnetic ble only during the 2030s with next generation neutrino de- counterpart comes from aligned and misaligned short GRBs (see Ta- tectors, will allow us to answer long-standing questions on ble 1) for which redshift can be measured. These numbers are con- the acceleration mechanisms inside these systems, on which servative estimates from afterglow simulations performed with “after- (hadronic vs. leptonic) processes characterize the photon and glowpy” (see text). neutrino production, and on the role of different type of sources in producing the observed diffuse neutrino flux. with dramatic magnetic field readjustments possibly caus- While AGNs are thought to produce the largest fraction ing fractures of the solid crust on their surface. Of particu- of such neutrinos, another, smaller fraction of diffuse neu- lar interest are the rare “giant flares” already observed from trino emission is expected to originate from SNe in starburst three different soft gamma repeaters (e.g., [131]; [129,130] galaxies that are expected to behave as calorimeters [145]. ∗ 9 and refs. therein; see also [132]), which inevitably excite Starburst galaxies have typically masses M <10 M [146] strong non-radial oscillation modes that may produce de- and obey the relation between M ∗ and the galaxy K-band ∗ tectable GWs (e.g., [133,134,135,136]). At the typical dom- luminosity (LK ) that is log[(M /M )(L /LK )] < −0.3 inant (i.e. f-mode) oscillation frequencies in NSs (∼kHz), [147,148], which is valid also for low-mass star-forming ET and CE might be sensitive to relatively close giant flare galaxies. This implies an absolute magnitude MK > −21.3. events (see also [137,138,139]). With a H-band limit ∼ 21 (AB) and assuming a negligible In terms of EM observations, magnetar bursts are com- H-K color, THESEUS/IRT could observe such galaxies up monly detected in the X-ray and soft gamma-ray bands (e.g., to z ∼ 0.6. [129,130]).9 The initial short (<0.5 s) bright spikes of giant An additional, still very uncertain fraction of neutrino flares can be detected with THESEUS/XGIS to considerable diffuse emission can originate from GRBs. If during the distances, favoured by its low energy threshold with respect GRB prompt phase a non-negligible fraction of baryons is to other coded-mask detectors. The following bursting ac- accelerated at internal shocks [149], neutrinos are likely to tivity is instead easily detectable with SXI. be produced in proton-photon interactions, given the intense radiation field of the jet. So far, no neutrino event has been detected in correlation with a GRB [150,151], indicating a 4 Neutrino sources limited neutrino production in the most powerful sources [152] and strengthening the case for extending this inves- High-energy neutrinos provide unique signatures of the pres- tigation to fainter sources. For this reason, LLGRBs may ence of accelerated hadrons at the source. Emerging from be better candidates than bright GRBs to account for the hadronic collisions with characteristic energies 20 times IceCube diffuse neutrino flux, although likely not dominant smaller than the energy of the accelerated protons, the prop- [153,154]. The sensitivity and extended energy bandpass erties of the neutrino events detected so far point towards of THESEUS are fundamental to probe the poorly-sampled cosmic objects capable of producing energies as high as EeV. fraction of intrinsically soft LLGRBs (see also Section 3.1). These sources are possibly responsible for the flux of Ultra In short GRBs, proton-proton collisions in the post-merger accretion disk are also expected to take place and contribute 9 Notably, a millisecond-duration radio burst was recently observed to the neutrino emission. As for long GRBs, no neutrino from a Galactic magnetar [140,141] along with a high-energy counter- part [142], strengthening the putative link between magnetar flares and event has been detected so far in coincidence with a short Fast Radio Bursts. GRB [150,151,152]. Recent studies have suggested that high- 14 Riccardo Ciolfi et al. energy neutrinos can be efficiently produced during the Ex- of star-bursting galaxies within neutrino sky localization re- tended Emission phase of short GRBs [150,151], a target gion (for well localized events only, i.e. < 1 deg2) (see also that THESEUS/XGIS will detect up to large distances (see Section 4). also Section 2.1.1).
5 External triggers 6 Conclusions
In addition to the major contribution of THESEUS in multi- Multi-messenger observations of GW and neutrino sources messenger astronomy in standard survey mode, enabled by have led to a number of breakthrough discoveries in the last its capability to cover large portions of the sky and indepen- few years. The cases of the short GRB 170817A and the dently discover the EM counterparts of neutrino or gravita- blazar TXS0506+056 proved that among the most promis- tional wave sources, it will also be possible to activate Target ing EM counterparts of these sources, X-ray and gamma-ray of Opportunity (ToO) observations pointing in the direction transient signals play a central role. Therefore, high-energy of a given GW or neutrino trigger event. Since the local- transient sky surveyors will certainly be of the utmost im- ization of GW and neutrino events can be of the order of portance for the future of multi-messenger astrophysics. a few square degrees or even worse, ToOs with THESEUS Thanks to its unique capabilities, THESEUS will inde- will also exploit the large sky coverage of XGIS and SXI to pendently detect and characterize the main EM counterparts identify the EM counterparts. At the same time, THESEUS of multi-messenger sources in an era in which next genera- capabilities to localize these sources down to a few arcmin tion neutrino and GW facilities will ensure much higher de- will be fundamental to activate further observations via ded- tection rates than today. Events like short GRBs, long GRBs icated follow-up campaigns with optical and radio facilities, and low-luminosity GRBs, AGNs and blazars, as well as X- ultimately characterizing the source and possibly identifying ray emission from bursting (e.g., SGRs) or spinning-down the host galaxy. NSs all represent ideal targets for THESEUS. Moreover, this While the nominal mission requirement for THESEUS mission will disseminate alerts of newly discovered multi- corresponds to a pointing time within about 12 hours since messenger sources with accurate sky localisation, which will the alert from neutrino or GW detectors, a realistic goal is be crucial to allow coeval narrow field facilities to perform to follow-up within 4 hours. With such premises, there are deep follow-up observations. a number of potential target signals. In the context of NS- Given the design sensitivities of next generation GW de- NS/NS-BH mergers, late time X-ray emission that could be tectors (such as ET and CE) and neutrino detectors (such as observed by THESEUS a few hours after the merger (i.e. the IceCube-Gen2 and KM3NeT), as well as those of several fu- GW trigger) is predicted in various forms, including HLE ture radio/optical/X-ray/gamma-ray facilities such as SKA, from a structured short GRB jet and, for NS-NS mergers ELT, CTA, and Athena (among others), the 2030s will be a only, SPDT from a long-lived highly magnetized NS rem- golden era of multi-messenger astrophysics. The expected nant (see Sections 2.1.2 and 2.2.1). Moreover, short GRB jet launch epoch of THESEUS (early 2030s) and its perfor- afterglows in both X-rays and NIR might have peak times mances make this mission timely and perfectly suited to face significantly delayed with respect to the initial burst (Sec- the future challenges posed by the multi-messenger investi- tion 10) and thus be observable in ToO mode by SXI and gation of the transient Universe, offering excellent prospects IRT. Finally, thermal kilonova NIR transients are expected for a major contribution in the field. to peak on timescales of days to weeks (Section 11) and could therefore be observed with IRT provided that a good Acknowledgements We acknowledge support from the ASI-INAF localization (of the order of arcminutes) is previously ob- agreement n. 2018-29-HH.0. MB and RH acknowledge the support of tained via an optical/IR detection. Observations of CCSNe the European Union’s Horizon 2020 Programme under the AHEAD2020 triggered by a GW precursor represent another possible ToO Project grant agreement 871158. Part of this research was conducted by the Australian Research Council Centre of Excellence for Gravitational application, aimed at catching, e.g., shock-breakout X-ray Wave Discovery (OzGrav), through project number CE170100004. EH signals (in events like SN 2008D the time-delay can be of also acknowledges support from an Australian Research Council DE- several hours). CRA Fellowship (DE170100891). AR acknowledges support from the THESEUS ToO observations of neutrino events will be project Supporto Arizona & Italia. LSal acknowledges support from the Irish Research Council under grant GOIPG/2017/1525. LH ac- crucial to enhance the confidence in establishing their cos- knowledges support from Science Foundation Ireland under grant mic origin and to provide a complete phenomenological pic- 19/FFP/6777 and from the EU AHEAD2020 project (grant agreement ture of the corresponding sources and underlying neutrino 871158). PDA acknowledges funding from the Italian Space Agency, production mechanisms. Compatible with the THESEUS re- contract ASI/INAF n. I/004/11/4. MB, PDA, and EP acknowledge sup- port from PRIN-MIUR 2017 (grant 20179ZF5KS). MDP acknowl- action timescales are, for instance, the flaring activity of edges support for this work by the Scientific and Technological Re- AGNs with time-scales of hours/days or NIR observations search Council of Turkey (TUBITAK),¨ Grant No: MFAG-119F073. Multi-Messenger Astrophysics with THESEUS in the 2030s 15
References 18. W.B. Atwood, A.A. Abdo, M. Ackermann, W. Althouse, B. An- derson, M. Axelsson, L. Baldini, J. Ballet, D.L. Band, G. Barbi- 1. B.P. Abbott, R. Abbott, T.D. Abbott, M.R. Abernathy, F. Acer- ellini, et al., Astrophys. J. 697(2), 1071 (2009). DOI 10.1088/ nese, K. Ackley, C. Adams, T. Adams, P. Addesso, R.X. Ad- 0004-637X/697/2/1071 hikari, et al., Phys. Rev. Lett. 116(6), 061102 (2016). DOI 19. C. Meegan, G. Lichti, P.N. Bhat, E. Bissaldi, M.S. Briggs, 10.1103/PhysRevLett.116.061102 V. Connaughton, R. Diehl, G. Fishman, J. Greiner, A.S. Hoover, 2. B.P. Abbott, R. Abbott, T.D. Abbott, M.R. Abernathy, F. Acer- et al., Astrophys. J. 702(1), 791 (2009). DOI 10.1088/ nese, K. Ackley, C. Adams, T. Adams, P. Addesso, R.X. Ad- 0004-637X/702/1/791 20. C. Winkler, T.J.L. Courvoisier, G. Di Cocco, N. Gehrels, hikari, et al., Phys. Rev. Lett. 116(24), 241103 (2016). DOI A. Gimenez,´ S. Grebenev, W. Hermsen, J.M. Mas-Hesse, F. Le- 10.1103/PhysRevLett.116.241103 brun, N. Lund, et al., Astron. Astrophys. 411, L1 (2003). DOI 3. R. Abbott, T.D. Abbott, S. Abraham, F. Acernese, K. Ackley, 10.1051/0004-6361:20031288 A. Adams, C. Adams, R.X. Adhikari, V.B. Adya, C. Affeldt, 21. J. Wei, B. Cordier, S. Antier, P. Antilogus, J.L. Atteia, A. Bajat, et al., arXiv e-prints arXiv:2010.14527 (2020) S. Basa, V. Beckmann, M.G. Bernardini, S. Boissier, et al., arXiv 4. B.P. Abbott, R. Abbott, T.D. Abbott, F. Acernese, K. Ackley, e-prints arXiv:1610.06892 (2016) C. Adams, T. Adams, P. Addesso, R.X. Adhikari, V.B. Adya, 22. M. Bailes, B.K. Berger, P.R. Brady, M. Branchesi, K. Danz- et al., Phys. Rev. Lett. 119(16), 161101 (2017). DOI 10.1103/ mann, M. Evans, K. Holley-Bockelmann, B.R. Iyer, T. Kajita, PhysRevLett.119.161101 S. Katsanevas, et al., Nature Rev. Phys. (2021). DOI 10.1038/ 5. B.P. Abbott, R. Abbott, T.D. Abbott, S. Abraham, F. Acernese, s42254-021-00303-8 K. Ackley, C. Adams, R.X. Adhikari, V.B. Adya, C. Affeldt, 23. M. Punturo, M. Abernathy, F. Acernese, B. Allen, N. Ander- et al., Astrophys. J. Lett. 892(1), L3 (2020). DOI 10.3847/ sson, K. Arun, F. Barone, B. Barr, M. Barsuglia, M. Beker, 2041-8213/ab75f5 et al., Class. Quantum Grav. 27(19), 194002 (2010). DOI 6. R. Abbott, T.D. Abbott, S. Abraham, F. Acernese, K. Ackley, 10.1088/0264-9381/27/19/194002 C. Adams, R.X. Adhikari, V.B. Adya, C. Affeldt, M. Agathos, 24. IceCube-Gen2 Collaboration, arXiv e-prints arXiv:1412.5106 et al., Astrophys. J. Lett. 896(2), L44 (2020). DOI 10.3847/ (2014) 2041-8213/ab960f 25. M. Maggiore, C. Van Den Broeck, N. Bartolo, E. Belgacem, 7. J. Aasi, B.P. Abbott, R. Abbott, T. Abbott, M.R. Abernathy, D. Bertacca, M.A. Bizouard, M. Branchesi, S. Clesse, S. Foffa, K. Ackley, C. Adams, T. Adams, P. Addesso, R.X. Adhikari, J. Garc´ıa-Bellido, et al., J. Cosmol. Astropart. Phys. 2020(3), 050 et al., Class. Quantum Grav. 32(7), 074001 (2015). DOI (2020). DOI 10.1088/1475-7516/2020/03/050 10.1088/0264-9381/32/7/074001 26. M.L. Chan, C. Messenger, I.S. Heng, M. Hendry, Phys. Rev. D 97(12), 123014 (2018). DOI 10.1103/PhysRevD.97.123014 8. F. Acernese, M. Agathos, K. Agatsuma, D. Aisa, N. Alleman- 27. IceCube Collaboration, Science 342(6161), 1242856 (2013). dou, A. Allocca, J. Amarni, P. Astone, G. Balestri, G. Bal- DOI 10.1126/science.1242856 lardin, et al., Class. Quantum Grav. 32(2), 024001 (2015). DOI 28. M.G. Aartsen, M. Ackermann, J. Adams, J.A. Aguilar, 10.1088/0264-9381/32/2/024001 M. Ahlers, M. Ahrens, I.A. Samarai, D. Altmann, K. Andeen, 9. B.P. Abbott, R. Abbott, T.D. Abbott, S. Abraham, F. Acernese, T. Anderson, et al., Astrophys. J. 843(2), 112 (2017). DOI K. Ackley, C. Adams, V.B. Adya, C. Affeldt, M. Agathos, et al., 10.3847/1538-4357/aa7569 Phys. Rev. D 101(8), 084002 (2020). DOI 10.1103/PhysRevD. 29. IceCube Collaboration, Science 361(6398), eaat1378 (2018). 101.084002 DOI 10.1126/science.aat1378 10. B.P. Abbott, R. Abbott, T.D. Abbott, S. Abraham, F. Acernese, 30. S. Adrian-Mart´ ´ınez, M. Ageron, F. Aharonian, S. Aiello, A. Al- K. Ackley, C. Adams, R.X. Adhikari, V.B. Adya, C. Affeldt, bert, F. Ameli, E. Anassontzis, M. Andre, G. Androulakis, et al., Phys. Rev. D 100(2), 024004 (2019). DOI 10.1103/ M. Anghinolfi, et al., J. Phys. G Nucl. Phys. 43(8), 084001 PhysRevD.100.024004 (2016). DOI 10.1088/0954-3899/43/8/084001 11. I. Bartos, B. Kocsis, Z. Haiman, S. Marka,´ Astrophys. J. 835(2), 31. M. Agostini, M. Bohmer,¨ J. Bosma, K. Clark, M. Danninger, 165 (2017). DOI 10.3847/1538-4357/835/2/165 C. Fruck, R. Gernhauser,¨ A. Gartner,¨ D. Grant, F. Hen- 12. B.P. Abbott, R. Abbott, T.D. Abbott, F. Acernese, K. Ackley, ningsen, et al., Nature Astron. 4, 913 (2020). DOI 10.1038/ C. Adams, T. Adams, P. Addesso, R.X. Adhikari, V.B. Adya, s41550-020-1182-4 et al., Astrophys. J. Lett. 848, L13 (2017). DOI 10.3847/ 32. A.D. Avrorin, A.V. Avrorin, V.M. Aynutdinov, R. Bannash, I.A. 2041-8213/aa920c Belolaptikov, V.B. Brudanin, N.M. Budnev, A.A. Doroshenko, 13. B.P. Abbott, R. Abbott, T.D. Abbott, F. Acernese, K. Ackley, G.V. Domogatsky, R. Dvornicky,´ et al., in European Physical C. Adams, T. Adams, P. Addesso, R.X. Adhikari, V.B. Adya, Journal Web of Conferences, European Physical Journal Web et al., Astrophys. J. Lett. 848, L12 (2017). DOI 10.3847/ of Conferences, vol. 191 (2018), European Physical Journal 2041-8213/aa91c9 Web of Conferences, vol. 191, p. 01006. DOI 10.1051/epjconf/ 201819101006 14. K. Somiya, Class. Quantum Grav. 29(12), 124007 (2012). DOI 33. M. Santander, in 42nd COSPAR Scientific Assembly, vol. 42 10.1088/0264-9381/29/12/124007 (2018), vol. 42, pp. E1.17–24–18 15. B.P. Abbott, R. Abbott, T.D. Abbott, S. Abraham, F. Acer- 34. B.P. Abbott, R. Abbott, T.D. Abbott, M.R. Abernathy, F. Acer- nese, K. Ackley, C. Adams, V.B. Adya, C. Affeldt, M. Agathos, nese, K. Ackley, C. Adams, T. Adams, P. Addesso, R.X. Ad- et al., Liv. Rev. Rel. 23(1), 3 (2020). DOI 10.1007/ hikari, et al., Astrophys. J. 841(2), 89 (2017). DOI 10.3847/ s41114-020-00026-9 1538-4357/aa6c47 16. D. Reitze, R.X. Adhikari, S. Ballmer, B. Barish, L. Barsotti, 35. A. Goldstein, P. Veres, E. Burns, M.S. Briggs, R. Hamburg, G. Billingsley, D.A. Brown, Y. Chen, D. Coyne, et al., in Bulletin D. Kocevski, C.A. Wilson-Hodge, R.D. Preece, S. Poolakkil, of the American Astronomical Society, vol. 51 (2019), vol. 51, O.J. Roberts, et al., Astrophys. J. Lett. 848, L14 (2017). DOI p. 35 10.3847/2041-8213/aa8f41 17. N. Gehrels, G. Chincarini, P. Giommi, K.O. Mason, J.A. Nousek, 36. V. Savchenko, C. Ferrigno, E. Kuulkers, A. Bazzano, A.A. Wells, N.E. White, S.D. Barthelmy, D.N. Burrows, L.R. E. Bozzo, S. Brandt, J. Chenevez, T.J.L. Courvoisier, R. Diehl, Cominsky, et al., Astrophys. J. 611, 1005 (2004). DOI 10.1086/ A. Domingo, et al., Astrophys. J. Lett. 848, L15 (2017). DOI 422091 10.3847/2041-8213/aa8f94 16 Riccardo Ciolfi et al.
37. E. Troja, L. Piro, H. van Eerten, R.T. Wollaeger, M. Im, O.D. 60. O. Just, M. Obergaulinger, H.T. Janka, A. Bauswein, N. Schwarz, Fox, N.R. Butler, S.B. Cenko, T. Sakamoto, C.L. Fryer, et al., Astrophys. J. Lett. 816, L30 (2016). DOI 10.3847/2041-8205/ Nature 551, 71 (2017). DOI 10.1038/nature24290 816/2/L30 38. R. Margutti, E. Berger, W. Fong, C. Guidorzi, K.D. Alexander, 61. M. Ruiz, R.N. Lang, V. Paschalidis, S.L. Shapiro, Astrophys. J. B.D. Metzger, P.K. Blanchard, P.S. Cowperthwaite, R. Chornock, Lett. 824, L6 (2016). DOI 10.3847/2041-8205/824/1/L6 T. Eftekhari, et al., Astrophys. J. Lett. 848, L20 (2017). DOI 62. R. Ciolfi, Mon. Not. R. Astron. Soc. Lett. 495(1), L66 (2020). 10.3847/2041-8213/aa9057 DOI 10.1093/mnrasl/slaa062 39. G. Hallinan, A. Corsi, K.P. Mooley, K. Hotokezaka, E. Nakar, 63. R. Ciolfi, D.M. Siegel, Astrophys. J. Lett. 798, L36 (2015). DOI M.M. Kasliwal, D.L. Kaplan, D.A. Frail, S.T. Myers, T. Murphy, 10.1088/2041-8205/798/2/L36 et al., Science 358, 1579 (2017). DOI 10.1126/science.aap9855 64. L. Rezzolla, P. Kumar, Astrophys. J. 802(2), 95 (2015). DOI 40. K.D. Alexander, E. Berger, W. Fong, P.K.G. Williams, 10.1088/0004-637X/802/2/95 C. Guidorzi, R. Margutti, B.D. Metzger, J. Annis, P.K. Blan- 65. R. Ciolfi, Int. J. Mod. Phys. D 27, 1842004 (2018). DOI 10.1142/ chard, D. Brout, et al., Astrophys. J. Lett. 848, L21 (2017). DOI S021827181842004X 10.3847/2041-8213/aa905d 66. S. Ai, H. Gao, B. Zhang, Astrophys. J. 893(2), 146 (2020). DOI 41. K.P. Mooley, E. Nakar, K. Hotokezaka, G. Hallinan, A. Corsi, 10.3847/1538-4357/ab80bd D.A. Frail, A. Horesh, T. Murphy, E. Lenc, D.L. Kaplan, et al., 67. J.P. Norris, J.T. Bonnell, Astrophys. J. 643(1), 266 (2006). DOI Nature 554, 207 (2018). DOI 10.1038/nature25452 10.1086/502796 42. D. Lazzati, R. Perna, B.J. Morsony, D. Lopez-Camara, 68. J.P. Norris, N. Gehrels, J.D. Scargle, Astrophys. J. 717(1), 411 M. Cantiello, R. Ciolfi, B. Giacomazzo, J.C. Workman, Phys. (2010). DOI 10.1088/0004-637X/717/1/411 Rev. Lett. 120(24), 241103 (2018). DOI 10.1103/PhysRevLett. 69. Z.F. Bostancı, Y. Kaneko, E. Go¨g˘us¸,¨ Mon. Not. R. Astron. Soc. 120.241103 428(2), 1623 (2013). DOI 10.1093/mnras/sts157 43. J.D. Lyman, G.P. Lamb, A.J. Levan, I. Mandel, N.R. Tan- 70. Y. Kaneko, Z.F. Bostancı, E. Go¨g˘us¸,¨ L. Lin, Mon. Not. R. Astron. vir, S. Kobayashi, B. Gompertz, J. Hjorth, A.S. Fruchter, Soc. 452(1), 824 (2015). DOI 10.1093/mnras/stv1286 T. Kangas, et al., Nature Astr. 2, 751 (2018). DOI 10.1038/ 71. S. Kisaka, K. Ioka, T. Sakamoto, Astrophys. J. 846(2), 142 s41550-018-0511-3 (2017). DOI 10.3847/1538-4357/aa8775 44. K.D. Alexander, R. Margutti, P.K. Blanchard, W. Fong, 72. S.D. Barthelmy, G. Chincarini, D.N. Burrows, N. Gehrels, E. Berger, A. Hajela, T. Eftekhari, R. Chornock, P.S. Cowperth- S. Covino, A. Moretti, P. Romano, P.T. O’Brien, C.L. Sarazin, waite, D. Giannios, et al., Astrophys. J. Lett. 863, L18 (2018). C. Kouveliotou, et al., Nature 438, 994 (2005). DOI 10.1038/ DOI 10.3847/2041-8213/aad637 nature04392 45. K.P. Mooley, A.T. Deller, O. Gottlieb, E. Nakar, G. Hallinan, 73. P.A. Evans, R. Willingale, J.P. Osborne, P.T. O’Brien, K.L. Page, S. Bourke, D.A. Frail, A. Horesh, A. Corsi, K. Hotokezaka, Na- C.B. Markwardt, S.D. Barthelmy, A.P. Beardmore, D.N. Bur- ture 561, 355 (2018). DOI 10.1038/s41586-018-0486-3 rows, C. Pagani, et al., Astron. Astrophys. 519, A102 (2010). 46. G. Ghirlanda, O.S. Salafia, Z. Paragi, M. Giroletti, J. Yang, DOI 10.1051/0004-6361/201014819 B. Marcote, J. Blanchard, I. Agudo, T. An, M.G. Bernardini, 74. N. Bucciantini, B.D. Metzger, T.A. Thompson, E. Quataert, Mon. et al., Science 363(6430), 968 (2019). DOI 10.1126/science. Not. R. Astron. Soc. 419(2), 1537 (2012). DOI 10.1111/j. aau8815 1365-2966.2011.19810.x 47. E. Nakar, Phys. Rep. 886, 1 (2020). DOI 10.1016/j.physrep. 75. D.M. Siegel, R. Ciolfi, Astrophys. J. 819, 14 (2016). DOI 10. 2020.08.008 3847/0004-637X/819/1/14 48. N.R. Tanvir, A.J. Levan, A.S. Fruchter, J. Hjorth, R.A. Hounsell, 76. D.M. Siegel, R. Ciolfi, Astrophys. J. 819, 15 (2016). DOI 10. K. Wiersema, R.L. Tunnicliffe, Nature 500, 547 (2013). DOI 3847/0004-637X/819/1/15 10.1038/nature12505 77. G. Oganesyan, S. Ascenzi, M. Branchesi, O.S. Salafia, 49. E. Berger, Ann. Rev. Astron. Astrophys. 52, 43 (2014). DOI S. Dall’Osso, G. Ghirlanda, Astrophys. J. 893(2), 88 (2020). DOI 10.1146/annurev-astro-081913-035926 10.3847/1538-4357/ab8221 50. S. Ascenzi, G. Oganesyan, M. Branchesi, R. Ciolfi, J. 78. S. Ascenzi, G. Oganesyan, O.S. Salafia, M. Branchesi, Plasma Phys. 87(1), 845870102 (2021). DOI 10.1017/ G. Ghirlanda, S. Dall’Osso, Astron. Astrophys. 641, A61 (2020). S0022377820001646 DOI 10.1051/0004-6361/202038265 51. G. Ghirlanda, O.S. Salafia, A. Pescalli, G. Ghisellini, R. Sal- 79. H.J. Lu,¨ B. Zhang, W.H. Lei, Y. Li, P.D. Lasky, Astrophys. J. vaterra, E. Chassande-Mottin, M. Colpi, F. Nappo, P. D’Avanzo, 805, 89 (2015). DOI 10.1088/0004-637X/805/2/89 A. Melandri, et al., Astron. Astrophys. 594, A84 (2016). DOI 80. P. Beniamini, J. Granot, R. Gill, Mon. Not. R. Astron. Soc. 10.1051/0004-6361/201628993 493(3), 3521 (2020). DOI 10.1093/mnras/staa538 52. D. Wanderman, T. Piran, Mon. Not. R. Astron. Soc. 448(4), 3026 81. S. Dall’Osso, G. Stratta, D. Guetta, S. Covino, G. De Cesare, (2015). DOI 10.1093/mnras/stv123 L. Stella, Astron. Astrophys. 526, A121 (2011). DOI 10.1051/ 53. K. Ioka, T. Nakamura, Mon. Not. R. Astron. Soc. 487(4), 4884 0004-6361/201014168 (2019). DOI 10.1093/mnras/stz1650 82. A. Rowlinson, P.T. O’Brien, B.D. Metzger, N.R. Tanvir, A.J. 54. O.S. Salafia, G. Ghirlanda, S. Ascenzi, G. Ghisellini, Astron. As- Levan, Mon. Not. R. Astron. Soc. 430, 1061 (2013). DOI trophys. 628, A18 (2019). DOI 10.1051/0004-6361/201935831 10.1093/mnras/sts683 55. B. Zhang, Front. Phys. 14(6), 64402 (2019). DOI 10.1007/ 83. G. Stratta, M.G. Dainotti, S. Dall’Osso, X. Hernandez, G. De Ce- s11467-019-0913-4 sare, Astrophys. J. 869(2), 155 (2018). DOI 10.3847/1538-4357/ 56. R. Gill, A. Nathanail, L. Rezzolla, Astrophys. J. 876(2), 139 aadd8f (2019). DOI 10.3847/1538-4357/ab16da 84. P. Mesz´ aros,´ M.J. Rees, Astrophys. J. 476(1), 232 (1997). DOI 57. D. Lazzati, R. Ciolfi, R. Perna, Astrophys. J. 898(1), 59 (2020). 10.1086/303625 DOI 10.3847/1538-4357/ab9a44 85. R. Sari, T. Piran, R. Narayan, Astrophys. J. Lett. 497(1), L17 58. L. Rezzolla, B. Giacomazzo, L. Baiotti, J. Granot, C. Kouve- (1998). DOI 10.1086/311269 liotou, M.A. Aloy, Astrophys. J. Lett. 732(11), L6 (2011). DOI 86. G.P. Lamb, J.D. Lyman, A.J. Levan, N.R. Tanvir, T. Kangas, A.S. 10.1088/2041-8205/732/1/L6 Fruchter, B. Gompertz, J. Hjorth, I. Mandel, S.R. Oates, et al., 59. V. Paschalidis, M. Ruiz, S.L. Shapiro, Astrophys. J. Lett. 806, Astrophys. J. Lett. 870(2), L15 (2019). DOI 10.3847/2041-8213/ L14 (2015). DOI 10.1088/2041-8205/806/1/L14 aaf96b Multi-Messenger Astrophysics with THESEUS in the 2030s 17
87. G.P. Lamb, S. Kobayashi, Mon. Not. R. Astron. Soc. 472(4), 111. N. Andersson, J. Baker, K. Belczynski, S. Bernuzzi, E. Berti, 4953 (2017). DOI 10.1093/mnras/stx2345 L. Cadonati, P. Cerda-Dur´ an,´ J. Clark, M. Favata, L.S. Finn, 88. G.P. Lamb, I. Mandel, L. Resmi, Mon. Not. R. Astron. Soc. et al., Class. Quantum Grav. 30(19), 193002 (2013). DOI 481(2), 2581 (2018). DOI 10.1093/mnras/sty2196 10.1088/0264-9381/30/19/193002 89. B. Zhang, Astrophys. J. Lett. 763(1), L22 (2013). DOI 10.1088/ 112. J. Powell, S.E. Gossan, J. Logue, I.S. Heng, Phys. Rev. D 94(12), 2041-8205/763/1/L22 123012 (2016). DOI 10.1103/PhysRevD.94.123012 90. Y.W. Yu, B. Zhang, H. Gao, Astrophys. J. Lett. 776, L40 (2013). 113. C. Cutler, Phys. Rev. D 66(8), 084025 (2002). DOI 10.1103/ DOI 10.1088/2041-8205/776/2/L40 PhysRevD.66.084025 114. A. Corsi, P. Mesz´ aros,´ Astrophys. J. 702(2), 1171 (2009). DOI 91. B.D. Metzger, A.L. Piro, Mon. Not. R. Astron. Soc. 439, 3916 10.1088/0004-637X/702/2/1171 (2014). DOI 10.1093/mnras/stu247 115. S. Dall’Osso, S.N. Shore, L. Stella, Mon. Not. R. Astron. Soc. 92. R. Ciolfi, W. Kastaun, J.V. Kalinani, B. Giacomazzo, Phys. Rev. 398(4), 1869 (2009). DOI 10.1111/j.1365-2966.2008.14054.x D 100(2), 023005 (2019). DOI 10.1103/PhysRevD.100.023005 116. L. Gualtieri, R. Ciolfi, V. Ferrari, Class. Quantum Grav. 28(11), 93. A.L. Piro, B. Giacomazzo, R. Perna, Astrophys. J. Lett. 844(2), 114014 (2011). DOI 10.1088/0264-9381/28/11/114014 L19 (2017). DOI 10.3847/2041-8213/aa7f2f 117. S. Dall’Osso, L. Stella, C. Palomba, Mon. Not. R. Astron. Soc. 94. P.A. Evans, S.B. Cenko, J.A. Kennea, S.W.K. Emery, N.P.M. 480(1), 1353 (2018). DOI 10.1093/mnras/sty1706 Kuin, O. Korobkin, R.T. Wollaeger, C.L. Fryer, K.K. Madsen, 118. P. Beniamini, K. Hotokezaka, A. van der Horst, C. Kouveliotou, F.A. Harrison, et al., Science 358(6370), 1565 (2017). DOI Mon. Not. R. Astron. Soc. 487(1), 1426 (2019). DOI 10.1093/ 10.1126/science.aap9580 mnras/stz1391 95. S. Sugita, N. Kawai, S. Nakahira, H. Negoro, M. Serino, T. Mi- 119. M.H. van Putten, Phys. Rev. Lett. 87(9), 091101 (2001). DOI hara, K. Yamaoka, M. Nakajima, Publ. Astron. Soc. Japan 70(4), 10.1103/PhysRevLett.87.091101 81 (2018). DOI 10.1093/pasj/psy076 120. K. Toma, K. Ioka, T. Sakamoto, T. Nakamura, Astrophys. J. 96. B.D. Metzger, Liv. Rev. Rel. 23(1), 1 (2019). DOI 10.1007/ 659(2), 1420 (2007). DOI 10.1086/512481 s41114-019-0024-0 121. F.J. Virgili, E.W. Liang, B. Zhang, Mon. Not. R. Astron. Soc. 97. Z.P. Jin, X. Li, Z. Cano, S. Covino, Y.Z. Fan, D.M. Wei, Astro- 392(1), 91 (2009). DOI 10.1111/j.1365-2966.2008.14063.x phys. J. Lett. 811(2), L22 (2015). DOI 10.1088/2041-8205/811/ 122. T. Sakamoto, D.Q. Lamb, N. Kawai, A. Yoshida, C. Graziani, 2/L22 E.E. Fenimore, T.Q. Donaghy, M. Matsuoka, M. Suzuki, 98. I. Arcavi, G. Hosseinzadeh, D.A. Howell, C. McCully, D. Poz- G. Ricker, et al., Astrophys. J. 629(1), 311 (2005). DOI nanski, D. Kasen, J. Barnes, M. Zaltzman, S. Vasylyev, D. Maoz, 10.1086/431235 et al., Nature 551(7678), 64 (2017). DOI 10.1038/nature24291 123. R. Ciolfi, Astrophys. J. 829(2), 72 (2016). DOI 10.3847/ 0004-637X/829/2/72 99. D.A. Coulter, R.J. Foley, C.D. Kilpatrick, M.R. Drout, A.L. Piro, 124. L.X. Li, Mon. Not. R. Astron. Soc. 375(1), 240 (2007). DOI B.J. Shappee, M.R. Siebert, J.D. Simon, N. Ulloa, D. Kasen, 10.1111/j.1365-2966.2006.11286.x et al., Science 358(6370), 1556 (2017). DOI 10.1126/science. 125. A.J. Levan, N.R. Tanvir, R.L.C. Starling, K. Wiersema, K.L. aap9811 Page, D.A. Perley, S. Schulze, G.A. Wynn, R. Chornock, 100. E. Pian, P. D’Avanzo, S. Benetti, M. Branchesi, E. Brocato, J. Hjorth, et al., Astrophys. J. 781(1), 13 (2014). DOI 10.1088/ S. Campana, E. Cappellaro, S. Covino, V. D’Elia, J.P.U. Fynbo, 0004-637X/781/1/13 et al., Nature 551(7678), 67 (2017). DOI 10.1038/nature24298 126. B.B. Zhang, B. Zhang, K. Murase, V. Connaughton, M.S. Briggs, 101. S.J. Smartt, T.W. Chen, A. Jerkstrand, M. Coughlin, E. Kankare, Astrophys. J. 787(1), 66 (2014). DOI 10.1088/0004-637X/787/ S.A. Sim, M. Fraser, C. Inserra, K. Maguire, K.C. Chambers, 1/66 et al., Nature 551(7678), 75 (2017). DOI 10.1038/nature24303 127. B. Gendre, G. Stratta, J.L. Atteia, S. Basa, M. Boer,¨ D.M. Cow- 102. D. Kasen, B. Metzger, J. Barnes, E. Quataert, E. Ramirez-Ruiz, ard, S. Cutini, V. D’Elia, E.J. Howell, A. Klotz, et al., Astrophys. Nature 551(7678), 80 (2017). DOI 10.1038/nature24453 J. 766(1), 30 (2013). DOI 10.1088/0004-637X/766/1/30 103. G.P. Lamb, N.R. Tanvir, A.J. Levan, A. de Ugarte Postigo, 128. B. Gendre, Q.T. Joyce, N.B. Orange, G. Stratta, J.L. Atteia, K. Kawaguchi, A. Corsi, P.A. Evans, B. Gompertz, D.B. Male- M. Boer,¨ Mon. Not. R. Astron. Soc. 486(2), 2471 (2019). DOI sani, K.L. Page, et al., Astrophys. J. 883(1), 48 (2019). DOI 10.1093/mnras/stz1036 10.3847/1538-4357/ab38bb 129. S. Mereghetti, Astron. Astrophys. Rev. 15(4), 225 (2008). DOI 104. A.G. Riess, S. Casertano, W. Yuan, J.B. Bowers, L. Macri, J.C. 10.1007/s00159-008-0011-z Zinn, D. Scolnic, Astrophys. J. Lett. 908(1), L6 (2021). DOI 130. R. Turolla, S. Zane, A.L. Watts, Rep. Prog. Phys. 78(11), 116901 10.3847/2041-8213/abdbaf (2015). DOI 10.1088/0034-4885/78/11/116901 105. B.P. Abbott, R. Abbott, T.D. Abbott, F. Acernese, K. Ackley, 131. C. Thompson, R.C. Duncan, Mon. Not. R. Astron. Soc. 275(2), C. Adams, T. Adams, P. Addesso, R.X. Adhikari, V.B. Adya, 255 (1995). DOI 10.1093/mnras/275.2.255 et al., Nature 551, 85 (2017). DOI 10.1038/nature24471 132. D. Svinkin, D. Frederiks, K. Hurley, R. Aptekar, S. Golenet- skii, A. Lysenko, A.V. Ridnaia, A. Tsvetkova, M. Ulanov, T.L. 106. E. Belgacem, Y. Dirian, S. Foffa, E.J. Howell, M. Maggiore, Cline, et al., Nature 589(7841), 211 (2021). DOI 10.1038/ T. Regimbau, J. Cosm. Astropart. Phys. 2019(8), 015 (2019). s41586-020-03076-9 DOI 10.1088/1475-7516/2019/08/015 133. K. Ioka, Mon. Not. R. Astron. Soc. 327(2), 639 (2001). DOI 896 107. G. Ryan, H. van Eerten, L. Piro, E. Troja, Astrophys. J. (2), 10.1046/j.1365-8711.2001.04756.x 166 (2020). DOI 10.3847/1538-4357/ab93cf 134. A. Corsi, B.J. Owen, Phys. Rev. D 83(10), 104014 (2011). DOI 108. A. Rossi, G. Stratta, E. Maiorano, D. Spighi, N. Masetti, 10.1103/PhysRevD.83.104014 E. Palazzi, A. Gardini, A. Melandri, L. Nicastro, E. Pian, et al., 135. R. Ciolfi, S.K. Lander, G.M. Manca, L. Rezzolla, Astrophys. J. Mon. Not. R. Astron. Soc. 493(3), 3379 (2020). DOI 10.1093/ Lett. 736(1), L6 (2011). DOI 10.1088/2041-8205/736/1/L6 mnras/staa479 136. R. Ciolfi, L. Rezzolla, Astrophys. J. 760(1), 1 (2012). DOI 10. 109. H.A. Bethe, Rev. Mod. Phys. 62(4), 801 (1990). DOI 10.1103/ 1088/0004-637X/760/1/1 RevModPhys.62.801 137. B.P. Abbott, R. Abbott, T.D. Abbott, S. Abraham, F. Acer- 110. J. Logue, C.D. Ott, I.S. Heng, P. Kalmus, J.H.C. Scargill, Phys. nese, K. Ackley, C. Adams, R.X. Adhikari, V.B. Adya, C. Af- Rev. D 86(4), 044023 (2012). DOI 10.1103/PhysRevD.86. feldt, et al., Astrophys. J. 874(2), 163 (2019). DOI 10.3847/ 044023 1538-4357/ab0e15 18 Riccardo Ciolfi et al.
138. B.P. Abbott, R. Abbott, T.D. Abbott, S. Abraham, F. Acernese, K. Ackley, C. Adams, R.X. Adhikari, V.B. Adya, C. Affeldt, et al., Phys. Rev. D 99(10), 104033 (2019). DOI 10.1103/ PhysRevD.99.104033 139. B.P. Abbott, R. Abbott, T.D. Abbott, S. Abraham, F. Acernese, K. Ackley, C. Adams, R.X. Adhikari, V.B. Adya, C. Affeldt, et al., Phys. Rev. D 100(2), 024017 (2019). DOI 10.1103/ PhysRevD.100.024017 140. CHIME/FRB Collaboration, B.C. Andersen, K.M. Bandura, M. Bhardwaj, A. Bij, M.M. Boyce, P.J. Boyle, C. Brar, T. Cas- sanelli, P. Chawla, T. Chen, et al., Nature 587(7832), 54 (2020). DOI 10.1038/s41586-020-2863-y 141. C.D. Bochenek, V. Ravi, K.V. Belov, G. Hallinan, J. Kocz, S.R. Kulkarni, D.L. McKenna, Nature 587(7832), 59 (2020). DOI 10.1038/s41586-020-2872-x 142. S. Mereghetti, V. Savchenko, C. Ferrigno, D. Gotz,¨ M. Rigoselli, A. Tiengo, A. Bazzano, E. Bozzo, A. Coleiro, T.J.L. Cour- voisier, et al., Astrophys. J. Lett. 898(2), L29 (2020). DOI 10.3847/2041-8213/aba2cf 143. G. Pagliaroli, C. Evoli, F.L. Villante, J. Cosm. Astrop. Phys. 2016(11), 004 (2016). DOI 10.1088/1475-7516/2016/11/004 144. P. Mesz´ aros,´ Ann. Rev. Nucl. Part. Sci. 67, 45 (2017). DOI 10.1146/annurev-nucl-101916-123304 145. E. Waxman, J. Bahcall, Phys. Rev. D 59(2), 023002 (1999). DOI 10.1103/PhysRevD.59.023002 146. J. Brinchmann, S. Charlot, S.D.M. White, C. Tremonti, G. Kauff- mann, T. Heckman, J. Brinkmann, Mon. Not. R. Astron. Soc. 351(4), 1151 (2004). DOI 10.1111/j.1365-2966.2004.07881.x 147. S. Arnouts, C.J. Walcher, O. Le Fevre,` G. Zamorani, O. Il- bert, V. Le Brun, L. Pozzetti, S. Bardelli, L. Tresse, E. Zucca, et al., Astron. Astrophys. 476(1), 137 (2007). DOI 10.1051/ 0004-6361:20077632 148. O. Ilbert, M. Salvato, E. Le Floc’h, H. Aussel, P. Capak, H.J. McCracken, B. Mobasher, J. Kartaltepe, N. Scoville, D.B. Sanders, et al., Astrophys. J. 709(2), 644 (2010). DOI 10.1088/ 0004-637X/709/2/644 149. G. Ghisellini, G. Ghirlanda, G. Oganesyan, S. Ascenzi, L. Nava, A. Celotti, O.S. Salafia, M.E. Ravasio, M. Ronchi, Astron. As- trophys. 636, A82 (2020). DOI 10.1051/0004-6361/201937244 150. M.G. Aartsen, K. Abraham, M. Ackermann, J. Adams, J.A. Aguilar, M. Ahlers, M. Ahrens, D. Altmann, T. Anderson, I. Ansseau, et al., Astrophys. J. 824(2), 115 (2016). DOI 10.3847/0004-637X/824/2/115 151. S. Adrian-Mart´ ´ınez, A. Albert, I.A. Samarai, M. Andre,´ M. Anghinolfi, G. Anton, S. Anvar, M. Ardid, T. Astraatmadja, J.J. Aubert, et al., Astron. Astrophys. 559, A9 (2013). DOI 10.1051/0004-6361/201322169 152. A. Albert, M. Andre,´ M. Anghinolfi, G. Anton, M. Ardid, J.J. Aubert, T. Avgitas, B. Baret, J. Barrios-Mart´ı, S. Basa, et al., Mon. Not. R. Astron. Soc. 469(1), 906 (2017). DOI 10.1093/ mnras/stx902 153. K. Murase, K. Ioka, S. Nagataki, T. Nakamura, Astrophys. J. Lett. 651(1), L5 (2006). DOI 10.1086/509323 154. P.B. Denton, I. Tamborra, Astrophys. J. 855(1), 37 (2018). DOI 10.3847/1538-4357/aaab4a