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  • 1. Ackley, K.
    et al.
    Amati, L.
    Barbieri, C.
    Bauer, F. E.
    Benetti, S.
    Bernardini, M. G.
    Bhirombhakdi, K.
    Botticella, M. T.
    Branchesi, M.
    Brocato, E.
    Bruun, S. H.
    Bulla, Mattia
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Campana, S.
    Cappellaro, E.
    Castro-Tirado, A. J.
    Chambers, K. C.
    Chaty, S.
    Chen, Ting-Wan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Max-Planck-Institut für Extraterrestrische Physik, Germany.
    Ciolfi, R.
    Coleiro, A.
    Copperwheat, C. M.
    Covino, S.
    Cutter, R.
    D'Ammando, F.
    D'Avanzo, P.
    De Cesare, G.
    D'Elia, V.
    Della Valle, M.
    Denneau, L.
    De Pasquale, M.
    Dhillon, V. S.
    Dyer, M. J.
    Elias-Rosa, N.
    Evans, P. A.
    Eyles-Ferris, R. A. J.
    Fiore, A.
    Fraser, M.
    Fruchter, A. S.
    Fynbo, J. P. U.
    Galbany, L.
    Gall, C.
    Galloway, D. K.
    Getman, F.
    Ghirlanda, G.
    Gillanders, J. H.
    Gomboc, A.
    Gompertz, B. P.
    Gonzalez-Fernandez, C.
    Gonzalez-Gaitan, S.
    Grado, A.
    Greco, G.
    Gromadzki, M.
    Groot, P. J.
    Gutierrez, C. P.
    Heikkila, T.
    Heintz, K. E.
    Hjorth, J.
    Hu, Y.-D.
    Huber, M. E.
    Inserra, C.
    Izzo, L.
    Japelj, J.
    Jerkstrand, Anders
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Jin, Z. P.
    Jonker, P. G.
    Kankare, E.
    Kann, D. A.
    Kennedy, M.
    Kim, S.
    Klose, S.
    Kool, Erik C.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kotak, R.
    Kuncarayakti, H.
    Lamb, G. P.
    Leloudas, G.
    Levan, A. J.
    Longo, F.
    Lowe, T. B.
    Lyman, J. D.
    Magnier, E.
    Maguire, K.
    Maiorano, E.
    Mandel, I.
    Mapelli, M.
    Mattila, S.
    McBrien, O. R.
    Melandri, A.
    Michalowski, M. J.
    Milvang-Jensen, B.
    Moran, S.
    Nicastro, L.
    Nicholl, M.
    Nicuesa Guelbenzu, A.
    Nuttal, L.
    Oates, S. R.
    O'Brien, P. T.
    Onori, F.
    Palazzi, E.
    Patricelli, B.
    Perego, A.
    Torres, M. A. P.
    Perley, D. A.
    Pian, E.
    Pignata, G.
    Piranomonte, S.
    Poshyachinda, S.
    Possenti, A.
    Pumo, M. L.
    Quirola-Vasquez, J.
    Ragosta, F.
    Ramsay, G.
    Rau, A.
    Rest, A.
    Reynolds, T. M.
    Rosetti, S. S.
    Rossi, A.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sabha, N. B.
    Sagués Carracedo, Ana
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Salafia, O. S.
    Salmon, L.
    Salvaterra, R.
    Savaglio, S.
    Sbordone, L.
    Schady, P.
    Schipani, P.
    Schultz, A. S. B.
    Schweyer, Tassilo
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Max-Planck-Institut für Extraterrestrische Physik, Germany.
    Smartt, S. J.
    Smith, K. W.
    Smith, M.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Srivastav, S.
    Stanway, E. R.
    Starling, R. L. C.
    Steeghs, D.
    Stratta, G.
    Stubbs, C. W.
    Tanvir, N. R.
    Testa, V.
    Thrane, E.
    Tonry, J. L.
    Turatto, M.
    Ulaczyk, K.
    van der Horst, A. J.
    Vergani, S. D.
    Walton, N. A.
    Watson, D.
    Wiersema, K.
    Wiik, K.
    Wyrzykowski, L.
    Yang, Sheng
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Yi, S.-X.
    Young, D. R.
    Observational constraints on the optical and near-infrared emission from the neutron star-black hole binary merger candidate S190814bv2020In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 643, article id A113Article in journal (Refereed)
    Abstract [en]

    Context. Gravitational wave (GW) astronomy has rapidly reached maturity, becoming a fundamental observing window for modern astrophysics. The coalescences of a few tens of black hole (BH) binaries have been detected, while the number of events possibly including a neutron star (NS) is still limited to a few. On 2019 August 14, the LIGO and Virgo interferometers detected a high-significance event labelled S190814bv. A preliminary analysis of the GW data suggests that the event was likely due to the merger of a compact binary system formed by a BH and a NS.

    Aims. In this paper, we present our extensive search campaign aimed at uncovering the potential optical and near infrared electromagnetic counterpart of S190814bv. We found no convincing electromagnetic counterpart in our data. We therefore use our non-detection to place limits on the properties of the putative outflows that could have been produced by the binary during and after the merger.

    Methods. Thanks to the three-detector observation of S190814bv, and given the characteristics of the signal, the LIGO and Virgo Collaborations delivered a relatively narrow localisation in low latency - a 50% (90%) credible area of 5 deg(2) (23 deg(2)) - despite the relatively large distance of 26752 Mpc. ElectromagNetic counterparts of GRAvitational wave sources at the VEry Large Telescope collaboration members carried out an intensive multi-epoch, multi-instrument observational campaign to identify the possible optical and near infrared counterpart of the event. In addition, the ATLAS, GOTO, GRAWITA-VST, Pan-STARRS, and VINROUGE projects also carried out a search on this event. In this paper, we describe the combined observational campaign of these groups.

    Results. Our observations allow us to place limits on the presence of any counterpart and discuss the implications for the kilonova (KN), which was possibly generated by this NS-BH merger, and for the strategy of future searches. The typical depth of our wide-field observations, which cover most of the projected sky localisation probability (up to 99.8%, depending on the night and filter considered), is r similar to 22 (resp. K similar to 21) in the optical (resp. near infrared). We reach deeper limits in a subset of our galaxy-targeted observations, which cover a total similar to 50% of the galaxy-mass-weighted localisation probability. Altogether, our observations allow us to exclude a KN with large ejecta mass M greater than or similar to 0.1 M-circle dot to a high (> 90%) confidence, and we can exclude much smaller masses in a sub-sample of our observations. This disfavours the tidal disruption of the neutron star during the merger.

    Conclusions. Despite the sensitive instruments involved in the campaign, given the distance of S190814bv, we could not reach sufficiently deep limits to constrain a KN comparable in luminosity to AT 2017gfo on a large fraction of the localisation probability. This suggests that future (likely common) events at a few hundred megaparsecs will be detected only by large facilities with both a high sensitivity and large field of view. Galaxy-targeted observations can reach the needed depth over a relevant portion of the localisation probability with a smaller investment of resources, but the number of galaxies to be targeted in order to get a fairly complete coverage is large, even in the case of a localisation as good as that of this event.

  • 2.
    Ahrens, Maryon
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bohm, Christian
    Stockholm University, Faculty of Science, Department of Physics.
    Conrad, Jan M.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Dumm, Jonathan P.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Finley, Chad
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Flis, Samuel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hultqvist, Klas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Walck, Christian
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zoll, Marcel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Meyer, Manuel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stanford University, USA.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Feindt, Ulrich
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Barbarino, Cristina
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bulla, Mattia
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Roy, Rupak
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Farnier, Christian
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Linnaeus University, Sweden.
    Morå, Knut
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Wagner, Robert M.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Multi-messenger Observations of a Binary Neutron Star Merger2017In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 848, no 2, article id L12Article in journal (Refereed)
    Abstract [en]

    On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of similar to 1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg(2) at a luminosity distance of 40(-8)(+8) Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 M-circle dot. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at similar to 40 Mpc) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over similar to 10 days. Following early non-detections, X-ray and radio emission were discovered at the transient's position similar to 9 and similar to 16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta.

  • 3. Amaro-Seoane, Pau
    et al.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Vigna-Gómez, Alejandro
    Astrophysics with the Laser Interferometer Space Antenna2023In: Living Reviews in Relativity, E-ISSN 1433-8351, Vol. 26, no 1, article id 2Article, review/survey (Refereed)
    Abstract [en]

    The Laser Interferometer Space Antenna (LISA) will be a transformative experiment for gravitational wave astronomy, and, as such, it will offer unique opportunities to address many key astrophysical questions in a completely novel way. The synergy with ground-based and space-born instruments in the electromagnetic domain, by enabling multi-messenger observations, will add further to the discovery potential of LISA. The next decade is crucial to prepare the astrophysical community for LISA’s first observations. This review outlines the extensive landscape of astrophysical theory, numerical simulations, and astronomical observations that are instrumental for modeling and interpreting the upcoming LISA datastream. To this aim, the current knowledge in three main source classes for LISA is reviewed; ultra-compact stellar-mass binaries, massive black hole binaries, and extreme or interme-diate mass ratio inspirals. The relevant astrophysical processes and the established modeling techniques are summarized. Likewise, open issues and gaps in our understanding of these sources are highlighted, along with an indication of how LISA could help making progress in the different areas. New research avenues that LISA itself, or its joint exploitation with upcoming studies in the electromagnetic domain, will enable, are also illustrated. Improvements in modeling and analysis approaches, such as the combination of numerical simulations and modern data science techniques, are discussed. This review is intended to be a starting point for using LISA as a new discovery tool for understanding our Universe.  

  • 4.
    Anderson, Brandon
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Larsson, Stefan
    Li, L.
    Meyer, Manuel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zimmer, Stephan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ferretti, Raphael
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    SUPPLEMENT: LOCALIZATION AND BROADBAND FOLLOW-UP OF THE GRAVITATIONAL-WAVE TRANSIENT GW150914 (2016, ApJL, 826, L13)2016In: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 225, no 1, article id 8Article in journal (Refereed)
    Abstract [en]

    This Supplement provides supporting material for Abbott et al. (2016a). We briefly summarize past electromagnetic (EM) follow-up efforts as well as the organization and policy of the current EM follow-up program. We compare the four probability sky maps produced for the gravitational-wave transient GW150914, and provide additional details of the EM follow-up observations that were performed in the different bands.

  • 5.
    Anderson, Brandon
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Meyer, Manuel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ferretti, Raphael
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zimmer, Stephan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    LOCALIZATION AND BROADBAND FOLLOW-UP OF THE GRAVITATIONAL-WAVE TRANSIENT GW 1509142016In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 826, no 1, article id L13Article in journal (Refereed)
    Abstract [en]

    A gravitational-wave (GW) transient was identified in data recorded by the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) detectors on 2015 September 14. The event, initially designated G184098 and later given the name GW150914, is described in detail elsewhere. By prior arrangement, preliminary estimates of the time, significance, and sky location of the event were shared with 63 teams of observers covering radio, optical, near-infrared, X-ray, and gamma-ray wavelengths with ground- and space-based facilities. In this Letter we describe the low-latency analysis of the GW data and present the sky localization of the first observed compact binary merger. We summarize the follow-up observations reported by 25 teams via private Gamma-ray Coordinates Network circulars, giving an overview of the participating facilities, the GW sky localization coverage, the timeline, and depth of the observations. As this event turned out to be a binary black hole merger, there is little expectation of a detectable electromagnetic (EM) signature. Nevertheless, this first broadband campaign to search for a counterpart of an Advanced LIGO source represents a milestone and highlights the broad capabilities of the transient astronomy community and the observing strategies that have been developed to pursue neutron star binary merger events. Detailed investigations of the EM data and results of the EM follow-up campaign are being disseminated in papers by the individual teams.

  • 6. Ascenzi, Stefano
    et al.
    Coughlin, Michael W.
    Dietrich, Tim
    Foley, Ryan J.
    Ramirez-Ruiz, Enrico
    Piranomonte, Silvia
    Mockler, Brenna
    Murguia-Berthier, Ariadna
    Fryer, Chris L.
    Lloyd-Ronning, Nicole M.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    A luminosity distribution for kilonovae based on short gamma-ray burst afterglows2019In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 486, no 1, p. 672-690Article in journal (Refereed)
    Abstract [en]

    The combined detection of a gravitational-wave signal, kilonova, and short gamma-ray burst (sGRB) from GW170817 marked a scientific breakthrough in the field of multimessenger astronomy. But even before GW170817, there have been a number of sGRBs with possible associated kilonova detections. In this work, we re-examine these ` historical' sGRB afterglows with a combination of state-of-the-art afterglow and kilonova models. This allows us to include optical/near-infrared synchrotron emission produced by the sGRB as well as ultraviolet/optical/near-infrared emission powered by the radioactive decay of r-process elements (i.e. the kilonova). Fitting the light curves, we derive the velocity and the mass distribution as well as the composition of the ejected material. The posteriors on kilonova parameters obtained from the fit were turned into distributions for the peak magnitude of the kilonova emission in different bands and the time at which this peak occurs. From the sGRB with an associated kilonova, we found that the peak magnitude in H bands falls in the range [-16.2, -13.1] (95 per cent of confidence) and occurs within 0.8-3.6 d after the sGRB prompt emission. In g band instead we obtain a peak magnitude in range [-16.8, -12.3] occurring within the first 18 h after the sGRB prompt. From the luminosity distributions of GW170817/AT2017gfo, kilonova candidates GRB130603B, GRB050709, and GRB060614 (with the possible inclusion of GRB150101B, GRB050724A, GRB061201, GRB080905A, GRB150424A, and GRB160821B) and the upper limits from all the other sGRBs not associated with any kilonova detection we obtain for the first time a kilonova luminosity distribution in different bands.

  • 7. Barack, Leor
    et al.
    Cardoso, Vitor
    Nissanke, Samaya
    Sotiriou, Thomas P.
    Askar, Abbas
    Belczynski, Chris
    Bertone, Gianfranco
    Bon, Edi
    Blas, Diego
    Brito, Richard
    Bulik, Tomasz
    Burrage, Clare
    Byrnes, Christian T.
    Caprini, Chiara
    Chernyakova, Masha
    Chruściel, Piotr
    Colpi, Monica
    Ferrari, Valeria
    Gaggero, Daniele
    Gair, Jonathan
    García-Bellido, Juan
    Hassan, Sayed Fawad
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Heisenberg, Lavinia
    Hendry, Martin
    Heng, Ik Siong
    Herdeiro, Carlos
    Hinderer, Tanja
    Horesh, Assaf
    Kavanagh, Bradley J.
    Kocsis, Bence
    Kramer, Michael
    Le Tiec, Alexandre
    Mingarelli, Chiara
    Nardini, Germano
    Nelemans, Gijs
    Palenzuela, Carlos
    Pani, Paolo
    Perego, Albino
    Porter, Edward K.
    Rossi, Elena M.
    Schmidt, Patricia
    Sesana, Alberto
    Sperhake, Ulrich
    Stamerra, Antonio
    Stein, Leo C.
    Tamanini, Nicola
    Tauris, Thomas M.
    Arturo Urena-López, L.
    Vincent, Frederic
    Volonteri, Marta
    Wardell, Barry
    Wex, Norbert
    Yagi, Kent
    Abdelsalhin, Tiziano
    Ángel Aloy, Miguel
    Amaro-Seoane, Pau
    Annulli, Lorenzo
    Arca-Sedda, Manuel
    Bah, Ibrahima
    Barausse, Enrico
    Barakovic, Elvis
    Benkel, Robert
    Bennett, Charles L.
    Bernard, Laura
    Bernuzzi, Sebastiano
    Berry, Christopher P. L.
    Berti, Emanuele
    Bezares, Miguel
    Juan Blanco-Pillado, Jose
    Blázquez-Salcedo, Jose Luis
    Bonetti, Matteo
    Bošković, Mateja
    Bosnjak, Zeljka
    Bricman, Katja
    Brügmann, Bernd
    Capelo, Pedro R.
    Carloni, Sante
    Cerdá-Durán, Pablo
    Charmousis, Christos
    Chaty, Sylvain
    Clerici, Aurora
    Coates, Andrew
    Colleoni, Marta
    Collodel, Lucas G.
    Compère, Geoffrey
    Cook, William
    Cordero-Carríon, Isabel
    Correia, Miguel
    de la Cruz-Dombriz, Álvaro
    Czinner, Viktor G.
    Destounis, Kyriakos
    Dialektopoulos, Kostas
    Doneva, Daniela
    Dotti, Massimo
    Drew, Amelia
    Eckner, Christopher
    Edholm, James
    Emparan, Roberto
    Erdem, Recai
    Ferreira, Miguel
    Ferreira, Pedro G.
    Finch, Andrew
    Font, Jose A.
    Franchini, Nicola
    Fransen, Kwinten
    Gal'tsov, Dmitry
    Ganguly, Apratim
    Gerosa, Davide
    Glampedakis, Kostas
    Gomboc, Andreja
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Gualtieri, Leonardo
    Guendelman, Eduardo
    Haardt, Francesco
    Harmark, Troels
    Hejda, Filip
    Hertog, Thomas
    Hopper, Seth
    Husa, Sascha
    Ihanec, Nada
    Ikeda, Taishi
    Jaodand, Amruta
    Jetzer, Philippe
    Jimenez-Forteza, Xisco
    Kamionkowski, Marc
    Kaplan, David E.
    Kazantzidis, Stelios
    Kimura, Masashi
    Kobayashi, Shiho
    Kokkotas, Kostas
    Krolik, Julian
    Kunz, Jutta
    Lämmerzahl, Claus
    Lasky, Paul
    Lemos, José P. S.
    Said, Jackson Levi
    Liberati, Stefano
    Lopes, Jorge
    Luna, Raimon
    Ma, Yin-Zhe
    Maggio, Elisa
    Mangiagli, Alberto
    Montero, Marina Martinez
    Maselli, Andrea
    Mayer, Lucio
    Mazumdar, Anupam
    Messenger, Christopher
    Ménard, Brice
    Minamitsuji, Masato
    Moore, Christopher J.
    Mota, David
    Nampalliwar, Sourabh
    Nerozzi, Andrea
    Nichols, David
    Nissimov, Emil
    Obergaulinger, Martin
    Obers, Niels A.
    Oliveri, Roberto
    Pappas, George
    Pasic, Vedad
    Peiris, Hiranya
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Petrushevska, Tanja
    Pollney, Denis
    Pratten, Geraint
    Rakic, Nemanja
    Racz, Istvan
    Radia, Miren
    Ramazanoglu, Fethi M.
    Ramos-Buades, Antoni
    Raposo, Guilherme
    Rogatko, Marek
    Rosca-Mead, Roxana
    Rosinska, Dorota
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ruiz-Morales, Ester
    Sakellariadou, Mairi
    Sanchis-Gual, Nicolás
    Salafia, Om Sharan
    Samajdar, Anuradha
    Sintes, Alicia
    Smole, Majda
    Sopuerta, Carlos
    Souza-Lima, Rafael
    Stalevski, Marko
    Stergioulas, Nikolaos
    Stevens, Chris
    Tamfal, Tomas
    Torres-Forne, Alejandro
    Tsygankov, Sergey
    Ünlütürk, Kivanç I.
    Valiante, Rosa
    van de Meent, Maarten
    Velhinho, José
    Verbin, Yosef
    Vercnocke, Bert
    Vernieri, Daniele
    Vicente, Rodrigo
    Vitagliano, Vincenzo
    Weltman, Amanda
    Whiting, Bernard
    Williamson, Andrew
    Witek, Helvi
    Wojnar, Aneta
    Yakut, Kadri
    Yan, Haopeng
    Yazadjiev, Stoycho
    Zaharijas, Gabrijela
    Zilhão, Miguel
    Black holes, gravitational waves and fundamental physics: a roadmap2019In: Classical and quantum gravity, ISSN 0264-9381, E-ISSN 1361-6382, Vol. 36, no 14, article id 143001Article, review/survey (Refereed)
    Abstract [en]

    The grand challenges of contemporary fundamental physics dark matter, dark energy, vacuum energy, inflation and early universe cosmology, singularities and the hierarchy problem all involve gravity as a key component. And of all gravitational phenomena, black holes stand out in their elegant simplicity, while harbouring some of the most remarkable predictions of General Relativity: event horizons, singularities and ergoregions. The hitherto invisible landscape of the gravitational Universe is being unveiled before our eyes: the historical direct detection of gravitational waves by the LIGO-Virgo collaboration marks the dawn of a new era of scientific exploration. Gravitational-wave astronomy will allow us to test models of black hole formation, growth and evolution, as well as models of gravitational-wave generation and propagation. It will provide evidence for event horizons and ergoregions, test the theory of General Relativity itself, and may reveal the existence of new fundamental fields. The synthesis of these results has the potential to radically reshape our understanding of the cosmos and of the laws of Nature. The purpose of this work is to present a concise, yet comprehensive overview of the state of the art in the relevant fields of research, summarize important open problems, and lay out a roadmap for future progress. This write-up is an initiative taken within the framework of the European Action on 'Black holes, Gravitational waves and Fundamental Physics'.

  • 8. Bernitt, Sonja
    et al.
    Bertone, Gianfranco
    Cardoso, Vitor
    Emparan, Roberto
    Galatyuk, Tetyana
    Kurkela, Aleksi
    Larsen, Ann-Cecilie
    Nahrgang, Marlene
    Nissanke, Samaya
    Pani, Paolo
    Porto, Rafael
    Riotto, Antonio
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fundamental Physics in the Gravitational-Wave Era2022In: Nuclear Physics News, ISSN 1061-9127, Vol. 32, no 1, p. 16-19Article in journal (Refereed)
  • 9.
    Camelio, Giovanni
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Dietrich, Tim
    Marques, Miguel
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Rotating neutron stars with nonbarotropic thermal profile2019In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 100, no 12, article id 123001Article in journal (Refereed)
    Abstract [en]

    Neutron stars provide an excellent laboratory for physics under the most extreme conditions. Up to now, models of axisymmetric, stationary, differentially rotating neutron stars were constructed under the strong assumption of barotropicity, where a one-to-one relation between all thermodynamic quantities exists. This implies that the specific angular momentum of a matter element depends only on its angular velocity. The physical conditions in the early stages of neutron stars, however, are determined by their violent birth processes, typically a supernova or in some cases the merger of two neutron stars, and detailed numerical models show that the resulting stars are by no means barotropic. Here, we construct models for stationary, differentially rotating, nonbarotropic neutron stars, where the equation of state and the specific angular momentum depend on more than one independent variable. We show that the potential formulation of the relativistic Euler equation can be extended to the nonbarotropic case, which, to the best of our knowledge, is a new result even for the Newtonian case. We implement the new method into the XNS code and construct equilibrium configurations for nonbarotropic equations of state. We scrutinize the resulting configurations by evolving them dynamically with the numerical relativity code BAM, thereby demonstrating that the new method indeed produces stationary, differentially rotating, nonbarotropic neutron star configurations.

  • 10.
    Camelio, Giovanni
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Dietrich, Tim
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Disc formation in the collapse of supramassive neutron stars2018In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 480, no 4, p. 5272-5285Article in journal (Refereed)
    Abstract [en]

    Short gamma-ray bursts (sGRBs) show a large diversity in their properties. This suggests that the observed phenomenon can be caused by different 'central engines' or that the engine produces a variety of outcomes depending on its parameters, or possibly both. The most popular engine scenario, the merger of two neutron stars, has received support from the recent Fermi and INTEGRAL detection of a burst of gamma rays (GRB170817A) following the neutron star merger GW 170817, but at the moment, it is not clear how peculiar this event potentially was. Several sGRBs engine models involve the collapse of a supramassive neutron star that produces a black hole plus an accretion disc. We study this scenario for a variety of equations of states both via angular momentum considerations based on equilibrium models and via fully dynamical Numerical Relativity simulations. We obtain a broader range of disc forming configurations than earlier studies but we agree with the latter that none of these configurations is likely to produce a phenomenon that would be classified as an sGRB.

  • 11.
    Camelio, Giovanni
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Polish Academy of Science, Poland.
    Dietrich, Tim
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Haskell, Brynmor
    Axisymmetric models for neutron star merger remnants with realistic thermal and rotational profiles2021In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 103, no 6, article id 063014Article in journal (Refereed)
    Abstract [en]

    Merging neutron stars are expected to produce hot, metastable remnants in rapid differential rotation, which subsequently cool and evolve into rigidly rotating neutron stars or collapse to black holes. Studying this metastable phase and its further evolution is essential for the prediction and interpretation of the electromagnetic, neutrino, and gravitational signals from such a merger. In this work, we model binary neutron star merger remnants and propose new rotation and thermal laws that describe postmerger remnants. Our framework is capable to reproduce quasiequilibrium configurations for generic equations of state, rotation and temperature profiles, including nonbarotropic ones. We demonstrate that our results are in agreement with numerical relativity simulations concerning bulk remnant properties like the mass, angular momentum, and the formation of a massive accretion disk. Because of the low computational cost for our axisymmetric code compared to full 3 + 1-dimensional simulations, we can perform an extensive exploration of the binary neutron star remnant parameter space studying several hundred thousand configurations for different equations of state.

  • 12.
    Chaurasia, Swami Vivekanandji
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Dietrich, Tim
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Black hole-neutron star simulations with the BAM code: First tests and simulations2021In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 104, no 8, article id 084010Article in journal (Refereed)
    Abstract [en]

    The first detections of black hole–neutron star mergers (GW200105 and GW200115) by the LIGO-Virgo-Kagra Collaboration mark a significant scientific breakthrough. The physical interpretation of pre- and postmerger signals requires careful cross-examination between observational and theoretical modelling results. Here we present the first set of black hole–neutron star simulations that were obtained with the numerical-relativity code BAM. Our initial data are constructed using the public LORENE spectral library, which employs an excision of the black hole interior. BAM, in contrast, uses the moving-puncture gauge for the evolution. Therefore, we need to “stuff” the black hole interior with smooth initial data to evolve the binary system in time. This procedure introduces constraint violations such that the constraint damping properties of the evolution system are essential to increase the accuracy of the simulation and in particular to reduce spurious center-of-mass drifts. Within BAM we evolve the Z4c equations and we compare our gravitational-wave results with those of the SXS collaboration and results obtained with the sacra code. While we find generally good agreement with the reference solutions and phase differences ≲0.5  rad at the moment of merger, the absence of a clean convergence order in our simulations does not allow for a proper error quantification. We finally present a set of different initial conditions to explore how the merger of black hole neutron star systems depends on the involved masses, spins, and equations of state.

  • 13. Dan, M.
    et al.
    Guillochon, J.
    Brüggen, M.
    Ramirez-Ruiz, E.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Thermonuclear detonations ensuing white dwarf mergers2015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 454, no 4, p. 4411-4428Article in journal (Refereed)
    Abstract [en]

    The merger of two white dwarfs (WDs) has for many years not been considered as the favoured model for the progenitor system of Type Ia supernovae (SNe Ia). But recent years have seen a change of opinion as a number of studies, both observational and theoretical, have concluded that they should contribute significantly to the observed SN Ia rate. In this paper, we study the ignition and propagation of detonation through post-merger remnants and we follow the resulting nucleosynthesis up to the point where a homologous expansion is reached. In our study we cover the entire range of WD masses and compositions. For the emergence of a detonation we study three different setups. The first two are guided by the merger remnants from our earlier simulations, while for the third one the ignitions were set by placing hotspots with properties determined by spatially resolved calculations taken from the literature. There are some caveats to our approach which we investigate. We carefully compare the nucleosynthetic yields of successful explosions with SN Ia observations. Only three of our models are consistent with all the imposed constraints and potentially lead to a standard Type Ia event. The first one, a 0.45 M-circle dot helium (He) + 0.9 M-circle dot carbon-oxygen (CO) WD system produces a sub-luminous, SN 1991bg-like event while the other two, a 0.45M(circle dot) He+1.1 M-circle dot oxygen-neon WD system and a 1.05 + 1.05 M-circle dot system with two CO WDs, are good candidates for common SNe Ia.

  • 14. Dan, Marius
    et al.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Brueggen, Marcus
    Podsiadlowski, Philipp
    The structure and fate of white dwarf merger remnants2014In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 438, no 1, p. 14-34Article in journal (Refereed)
    Abstract [en]

    We present a large parameter study where we investigate the structure of white dwarf (WD) merger remnants after the dynamical phase. A wide range of WD masses and compositions are explored, and we also probe the effect of different initial conditions. We investigated the degree of mixing between the WDs, the conditions for detonations as well as the amount of gas ejected. We find that systems with lower mass ratios have more total angular momentum and as a result more mass is flung out in a tidal tail. Nuclear burning can affect the amount of mass ejected. Many WD binaries that contain a helium-rich WD achieve the conditions to trigger a detonation. In contrast, for carbon-oxygen-transferring systems, only the most massive mergers with a total mass M greater than or similar to 2.1 M-circle dot detonate. Even systems with lower mass may detonate long after the merger if the remnant remains above the Chandrasekhar mass and carbon is ignited at the centre. Finally, our findings are discussed in the context of several possible observed astrophysical events and stellar systems, such as hot subdwarfs, R Coronae Borealis stars, single massive WDs, supernovae of Type Ia and other transient events. A large data base containing 225 WD merger remnants is made available via a dedicated web page.

  • 15. Diener, Peter
    et al.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Torsello, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Simulating neutron star mergers with the Lagrangian Numerical Relativity code SPHINCS _ BSSN2022In: European Physical Journal A, ISSN 1434-6001, E-ISSN 1434-601X, Vol. 58, no 4, article id 74Article in journal (Refereed)
    Abstract [en]

    We present the first neutron star merger simulations performed with the newly developed Numerical Relativity code SPHINCS_BSSN. This code evolves the spacetime on a mesh using the BSSN formulation, but matter is evolved via Lagrangian particles according to a high-accuracy version of general-relativistic Smooth Particle Hydrodynamics (SPH). Our code contains a number of new methodological elements compared to other Numerical Relativity codes. The main focus here is on the new elements that were introduced to model neutron star mergers. These include (a) a refinement (fixed in time) of the spacetime-mesh, (b) corresponding changes in the particle–mesh mapping algorithm and (c) a novel way to construct SPH initial data for binary systems via the recently developed “Artificial Pressure Method.” This latter method makes use of the spectral initial data produced by the library LORENE, and is implemented in a new code called SPHINCS_ID. While our main focus is on introducing these new methodological elements and documenting the current status of SPHINCS_BSSN, we also show as a first application a set of neutron star merger simulations employing “soft” (Γ=2.00Γ=2.00) and “stiff” (Γ=2.75Γ=2.75) polytropic equations of state.

  • 16. Eichler, M.
    et al.
    Arcones, A.
    Kelic, A.
    Korobkin, Oleg
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Langanke, K.
    Marketin, T.
    Martinez-Pinedo, G.
    Panov, I.
    Rauscher, T.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Winteler, C.
    Zinner, N. T.
    Thielemann, F. -K.
    THE ROLE OF FISSION IN NEUTRON STAR MERGERS AND ITS IMPACT ON THE r-PROCESS PEAKS2015In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 808, no 1, article id 30Article in journal (Refereed)
    Abstract [en]

    Comparing observational abundance features with nucleosynthesis predictions of stellar evolution or explosion simulations, we can scrutinize two aspects: (a) the conditions in the astrophysical production site and (b) the quality of the nuclear physics input utilized. We test the abundance features of r-process nucleosynthesis calculations for the dynamical ejecta of neutron star merger simulations based on three different nuclear mass models: The Finite Range Droplet Model, the (quenched version of the) Extended Thomas Fermi Model with Strutinsky Integral, and the Hartree-Fock-Bogoliubov mass model. We make use of corresponding fission barrier heights and compare the impact of four different fission fragment distribution models on the final r-process abundance distribution. In particular, we explore the abundance distribution in the second r-process peak and the rare-earth sub-peak as a function of mass models and fission fragment distributions, as well as the origin of a shift in the third r-process peak position. The latter has been noticed in a number of merger nucleosynthesis predictions. We show that the shift occurs during the r-process freeze-out when neutron captures and beta-decays compete and an (n,gamma)-(gamma,n) equilibrium is no longer maintained. During this phase neutrons originate mainly from fission of material above A = 240. We also investigate the role of beta-decay half-lives from recent theoretical advances, which lead either to a smaller amount of fissioning nuclei during freeze-out or a faster (and thus earlier) release of fission neutrons, which can (partially) prevent this shift and has an impact on the second and rare-earth peak as well.

  • 17. Evans, P. A.
    et al.
    Cenko, S. B.
    Kennea, J. A.
    Emery, S. W. K.
    Kuin, N. P. M.
    Korobkin, O.
    Wollaeger, R. T.
    Fryer, C. L.
    Madsen, K. K.
    Harrison, F. A.
    Xu, Y.
    Nakar, E.
    Hotokezaka, K.
    Lien, A.
    Campana, S.
    Oates, S. R.
    Troja, E.
    Breeveld, A. A.
    Marshall, F. E.
    Barthelmy, S. D.
    Beardmore, A. P.
    Burrows, D. N.
    Cusumano, G.
    D'Ai, A.
    D'Avanzo, P.
    D'Elia, V.
    De Pasquale, M.
    Even, W. P.
    Fontes, C. J.
    Forster, K.
    Garcia, J.
    Giommi, P.
    Grefenstette, B.
    Gronwall, C.
    Hartmann, D. H.
    Heida, M.
    Hungerford, A. L.
    Kasliwal, M. M.
    Krimm, H. A.
    Levan, A. J.
    Malesani, D.
    Melandri, A.
    Miyasaka, H.
    Nousek, J. A.
    O'Brien, P. T.
    Osborne, J. P.
    Pagani, C.
    Page, K. L.
    Palmer, D. M.
    Perri, M.
    Pike, S.
    Racusin, J. L.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Siegel, M. H.
    Sakamoto, T.
    Sbarufatti, B.
    Tagliaferri, G.
    Tanvir, N. R.
    Tohuvavohu, A.
    Swift and NuSTAR observations of GW170817: Detection of a blue kilonova2017In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 358, no 6370, p. 1565-1569Article in journal (Refereed)
    Abstract [en]

    With the first direct detection of merging black holes in 2015, the era of gravitational wave (GW) astrophysics began. A complete picture of compact object mergers, however, requires the detection of an electromagnetic (EM) counterpart. We report ultraviolet (UV) and x-ray observations by Swift and the Nuclear Spectroscopic Telescope Array of the EM counter part of the binary neutron star merger GW170817. The bright, rapidly fading UV emission indicates a high mass (approximate to 0.03 solar masses) wind-driven outflow with moderate electron fraction (Y-e approximate to 0.27). Combined with the x-ray limits, we favor an observer viewing angle of approximate to 30 degrees away from the orbital rotation axis, which avoids both obscuration from the heaviest elements in the orbital plane and a direct view of any ultrarelativistic, highly collimated ejecta (a gamma-ray burst afterglow).

  • 18. Eyles, R. A. J.
    et al.
    O'Brien, P. T.
    Wiersema, K.
    Starling, R. L. C.
    Gompertz, B. P.
    Lamb, G. P.
    Lyman, J. D.
    Levan, A. J.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Tanvir, N. R.
    An unusual transient following the short GRB 0712272019In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 489, no 1, p. 13-27Article in journal (Refereed)
    Abstract [en]

    We present X-ray and optical observations of the short duration gamma-ray burst GRB 071227 and its host at z= 0.381, obtained using Swift, Gemini South, and theVery Large Telescope. We identify a short-lived and moderately bright optical transient, with flux significantly in excess of that expected from a simple extrapolation of the X-ray spectrum at 0.2-0.3 d after burst. We fit the SED with afterglow models allowing for high extinction and thermal emission models that approximate a kilonova to assess the excess' origins. While some kilonova contribution is plausible, it is not favoured due to the low temperature and high luminosity required, implying superluminal expansion and a large ejectamass of similar to 0.1 M-circle dot. We find, instead, that the transient is broadly consistent with power-law spectra with additional dust extinction of E(B - V) similar to 0.4 mag, although a possibly thermal excess remains in the z band. We investigate the host, a spiral galaxy with an edge-on orientation, resolving its spectrum along its major axis to construct the galaxy rotation curve and analyse the star formation and chemical properties. The integrated host emission shows evidence for high extinction, consistent with the afterglow findings. The metallicity and extinction are consistent with previous studies of this host and indicate the galaxy is a typical, but dusty, late-type SGRB host.

  • 19. Farouqi, K.
    et al.
    Thielemann, F.-K.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kratz, K.-L.
    Correlations of r-process elements in very metal-poor stars as clues to their nucleosynthesis sites2022In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 663, article id A70Article in journal (Refereed)
    Abstract [en]

    Aims. Various nucleosynthesis studies have pointed out that the r-process elements in very metal-poor (VMP) halo stars might have different origins. By means of familiar concepts from statistics (correlations, cluster analysis, and rank tests of elemental abundances), we look for causally correlated elemental abundance patterns and attempt to link them to astrophysical events. Some of these events produce the r-process elements jointly with iron, while others do not have any significant iron contribution. We try to (a) characterize these different types of events by their abundance patterns and (b) identify them among the existing set of suggested r-process sites.

    Methods. The Pearson and Spearman correlation coefficients were used in order to investigate correlations among r-process elements (X,Y) as well as their relation to iron (Fe) in VMP halo stars. We gradually tracked the evolution of those coefficients in terms of the element enrichments [X/Fe] or [X/Y] and the metallicity [Fe/H]. This approach, aided by cluster analysis to find different structures of abundance patterns and rank tests to identify whether several events contributed to the observed pattern, is new and provides deeper insights into the abundances of VMP stars.

    Results. In the early stage of our Galaxy, at least three r-process nucleosynthesis sites have been active. The first two produce and eject iron and the majority of the lighter r-process elements. We assign them to two different types of core-collapse events, not identical to regular core-collapse supernovae (CCSNe), which produce only light trans-Fe elements. The third category is characterized by a strong r-process and is responsible for the major fraction of the heavy main r-process elements without a significant coproduction of Fe. It does not appear to be connected to CCSNe, in fact most of the Fe found in the related r-process enriched stars must come from previously occurring CCSNe. The existence of actinide boost stars indicates a further division among strong r-process sites. We assign these two strong r-process sites to neutron star mergers without fast black hole formation and to events where the ejecta are dominated by black hole accretion disk outflows. Indications from the lowest-metallicity stars hint at a connection with massive single stars (collapsars) forming black holes in the early Galaxy.

  • 20. Fernandez, Rodrigo
    et al.
    Quataert, Eliot
    Schwab, Josiah
    Kasen, Daniel
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    The interplay of disc wind and dynamical ejecta in the aftermath of neutron star-black hole mergers2015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 449, no 1, p. 390-402Article in journal (Refereed)
    Abstract [en]

    We explore the evolution of the different ejecta components generated during the merger of a neutron star and a black hole. Our focus is the interplay between material ejected dynamically during the merger, and the wind launched on a viscous time-scale by the remnant accretion disc. These components are expected to contribute to an electromagnetic transient and to produce r-process elements, each with a different signature when considered separately. Here we introduce a two-step approach to investigate their combined evolution, using two-and three-dimensional hydrodynamic simulations. Starting from the output of a merger simulation, we identify each component in the initial condition based on its phase-space distribution, and evolve the accretion disc in axisymmetry. The wind blown from this disc is injected into a three-dimensional computational domain where the dynamical ejecta is evolved. We find that the wind can suppress fallback accretion on time-scales longer than similar to 100 ms. Because of self-similar viscous evolution, the disc accretion at late times nevertheless approaches a power-law time dependence alpha t(-2.2). This can power some late-time gamma-ray burst engine activity, although the available energy is significantly less than in traditional fallback models. Inclusion of radioactive heating due to the r-process does not significantly affect the fallback accretion rate or the disc wind. We do not find any significant modification to the wind properties at large radius due to interaction with the dynamical ejecta. This is a consequence of the different expansion velocities of the two components.

  • 21. Fryer, Chris L.
    et al.
    Belczynski, Krzysztoff
    Ramirez-Ruiz, Enrico
    Rosswog, Stephan
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Shen, Gang
    Steiner, Andrew W.
    THE FATE OF THE COMPACT REMNANT IN NEUTRON STAR MERGERS2015In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 812, no 1, article id 24Article in journal (Refereed)
    Abstract [en]

    Neutron star (binary neutron star and neutron star-black hole) mergers are believed to produce short-duration gamma-ray bursts (GRBs). They are also believed to be the dominant source of gravitational waves to be detected by the advanced LIGO and advanced VIRGO and the dominant source of the heavy r-process elements in the universe. Whether or not these mergers produce short-duration GRBs depends sensitively on the fate of the core of the remnant (whether, and how quickly, it forms a black hole). In this paper, we combine the results of Newtonian merger calculations and equation of state studies to determine the fate of the cores of neutron star mergers. Using population studies, we can determine the distribution of these fates to compare to observations. We find that black hole cores form quickly only for equations of state that predict maximum non-rotating neutron star masses below 2.3-2.4 solar masses. If quick black hole formation is essential in producing GRBs, LIGO/Virgo observed rates compared to GRB rates could be used to constrain the equation of state for dense nuclear matter.

  • 22.
    Gafton, Emanuel
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Isaac Newton Group of Telescopes, Spain.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Tidal disruptions by rotating black holes: effects of spin and impact parameter2019In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 487, no 4, p. 4790-4808Article in journal (Refereed)
    Abstract [en]

    We present the results of relativistic smoothed particle hydrodynamics simulations of tidal disruptions of stars by rotating supermassive black holes, for a wide range of impact parameters and black hole spins. For deep encounters, we find that: relativistic precession creates debris geometries impossible to obtain with the Newtonian equations; part of the fluid can be launched on plunging orbits, reducing the fallback rate and the mass of the resulting accretion disc; multiple squeezings and bounces at periapsis may generate distinctive X-ray signatures resulting from the associated shock breakout; disruptions can occur inside the marginally bound radius, if the angular momentum spread launches part of the debris on non-plunging orbits. Perhaps surprisingly, we also find relativistic effects important in partial disruptions, where the balance between self-gravity and tidal forces is so precarious that otherwise minor relativistic effects can have decisive consequences on the stellar fate. In between, where the star is fully disrupted but relativistic effects are mild, the difference resides in a gentler rise of the fallback rate, a later and smaller peak, and longer return times. However, relativistic precession always causes thicker debris streams, both in the bound part (speeding up circularization) and in the unbound part (accelerating and enhancing the production of separate transients). We discuss various properties of the disruption (compression at periapsis, shape and spread of the energy distribution) and potential observables (peak fallback rate, times of rise and decay, duration of super-Eddington fallback) as a function of the impact parameter and the black hole spin.

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    fulltext
  • 23.
    Gafton, Emanuel
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Tejeda, Emilio
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Guillochon, J.
    Korobkin, Oleg
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Relativistic effects on tidal disruption kicks of solitary stars2015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 449, no 1, p. 771-780Article in journal (Refereed)
    Abstract [en]

    Solitary stars that wander too close to their galactic centres can become tidally disrupted, if the tidal forces due to the supermassive black hole residing there overcome the self-gravity of the star. If the star is only partially disrupted, so that a fraction survives as a self-bound object, this remaining core will experience a net gain in specific orbital energy, which translates into a velocity 'kick' of up to similar to 10(3) km s(-1). In this paper, we present the result of smoothed particle hydrodynamics simulations of such partial disruptions, and analyse the velocity kick imparted on the surviving core. We compare gamma = 5/3 and gamma = 4/3 polytropes disrupted in both a Newtonian potential, and a generalized potential that reproduces most relativistic effects around a Schwarzschild black hole either exactly or to excellent precision. For the Newtonian case, we confirm the results of previous studies that the kick velocity of the surviving core is virtually independent of the ratio of the black hole to stellar mass, and is a function of the impact parameter beta alone, reaching at most the escape velocity of the original star. For a given beta, relativistic effects become increasingly important for larger black holemasses. In particular, we find that the kick velocity increases with the black hole mass, making larger kicks more common than in the Newtonian case, as low-beta encounters are statistically more likely than high-beta encounters. The analysis of the tidal tensor for the generalized potential shows that our results are robust lower limits on the true relativistic kick velocities, and are generally in very good agreement with the exact results.

  • 24. Gall, Christa
    et al.
    Hjorth, Jens
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Tanvir, Nial R.
    Levan, Andrew J.
    Lanthanides or Dust in Kilonovae: Lessons Learned from GW1708172017In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 849, no 2, article id L19Article in journal (Refereed)
    Abstract [en]

    The unprecedented optical and near-infrared lightcurves of the first electromagnetic counterpart to a gravitationalwave source, GW170817, a binary neutron star merger, exhibited a strong evolution from blue to near-infrared (a so-called kilonova or macronova). The emerging near-infrared component is widely attributed to the formation of r-process elements that provide the opacity to shift the blue light into the near-infrared. An alternative scenario is that the light from the blue component gets extinguished by dust formed by the kilonova and subsequently is reemitted at near-infrared wavelengths. We test here this hypothesis using the lightcurves of AT 2017gfo, the kilonova accompanying GW170817. We find that of the order of 10(-5) M-circle dot. of carbon is required to reproduce the optical/near-infrared lightcurves as the kilonova fades. This putative dust cools from similar to 2000. K at similar to 4 days after the event to similar to 1500 K over the course of the following week, thus requiring dust with a high condensation temperature, such as carbon. We contrast this with the nucleosynthetic yields predicted by a range of kilonova wind models. These suggest that at most 10(-9) M-circle dot of carbon is formed. Moreover, the decay in the inferred dust temperature is slower than that expected in kilonova models. We therefore conclude that in current models of the blue component of the kilonova, the near-infrared component in the kilonova accompanying GW170817 is unlikely to be due to dust.

  • 25.
    Gizzi, Davide
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Lundman, Christoffer
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    O'Connor, Evan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Perego, A.
    Extension of the Advanced Spectral Leakage scheme for neutron star merger simulations2021In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 505, no 2, p. 2575-2593Article in journal (Refereed)
    Abstract [en]

    We calibrate a neutrino transport approximation, called Advanced Spectral Leakage (ASL), with the purpose of modelling neutrino-driven winds in neutron star mergers. Based on a number of snapshots, we gauge the ASL parameters by comparing against both the two-moment (M1) scheme implemented in the FLASH code and the Monte Carlo neutrino code SEDONU. The ASL scheme contains three parameters, the least robust of which results to be a blocking parameter for electron neutrinos and antineutrinos. The parameter steering the angular distribution of neutrino heating is recalibrated compared to the earlier work. We also present a new, fast and mesh-free algorithm for calculating spectral optical depths, which, when using smoothed-particle hydrodynamics (SPH), makes the neutrino transport completely particle-based. We estimate a speed-up of a factor of ≳100 in the optical depth calculation when comparing to a grid-based approach. In the suggested calibration we recover luminosities and mean energies within 25 per cent. A comparison of the rates of change of internal energy and electron fraction in the neutrino-driven wind suggests comparable accuracies of ASL and M1, but a higher computational efficiency of the ASL scheme. We estimate that the ratio between the CPU hours spent on the ASL neutrino scheme and those spent on the hydrodynamics is ≲0.8 per time-step when considering the SPH code MAGMA2 as source code for the Lagrangian hydrodynamics, to be compared with a factor of 10 from the M1 in FLASH.

  • 26.
    Gizzi, Davide
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    O’Connor, Evan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Perego, A.
    Cabezon, R. M.
    Nativi, Lorenzo
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    A multidimensional implementation of the Advanced Spectral neutrino Leakage scheme2019In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 490, no 3, p. 4211-4229Article in journal (Refereed)
    Abstract [en]

    We present a new, multidimensional implementation of the Advanced Spectral Leakage (ASL) scheme with the purpose of modelling neutrino–matter interactions in neutron star mergers. A major challenge is the neutrino absorption in the semitransparent regime, which is responsible for driving winds from the merger remnant. The composition of such winds is crucial in the understanding of the electromagnetic emission in the recently observed macronova following GW170817. Compared to the original version, we introduce an optical-depth-dependent flux factor to model the average angle of neutrino propagation, and a modulation that accounts for flux anisotropies in non-spherical geometries. We scrutinize our approach by first comparing the new scheme against the original one for a spherically symmetric core-collapse supernova snapshot, both in 1D and in 3D, and additionally against a two-moment (M1) scheme as implemented in 1D into the code GR1D. The luminosities and mean energies agree to a few per cents in most tests. Finally, for the case of a binary merger remnant snapshot we compare the new ASL scheme with the M1 scheme that is implemented in the Eulerian adaptive mesh refinement code FLASH. We find that the neutrino absorption distribution in the semitransparent regime is overall well reproduced. Both approaches agree to within 15 per cent for the average energies and to better than ∼ 35 per cent in the total luminosities.

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    paper_I_Gizzi
  • 27. Grossman, Doron
    et al.
    Korobkin, Oleg
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Piran, Tsvi
    The long-term evolution of neutron star merger remnants - II. Radioactively powered transients2014In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 439, no 1, p. 757-770Article in journal (Refereed)
    Abstract [en]

    We use 3D hydrodynamic simulations of the long-term evolution of neutron star merger ejecta to predict the light curves of electromagnetic transients that are powered by the decay of freshly produced r-process nuclei. For the dynamic ejecta that are launched by tidal and hydrodynamic interaction, we adopt grey opacities of 10 cm(2) g(-1), as suggested by recent studies. For our reference case of a 1.3-1.4 M-circle dot merger, we find a broad IR peak 2-4 d after the merger. The peak luminosity is approximate to 2 x 10(40) erg s(-1) for an average orientation, but increased by up to a factor of 4 for more favourable binary parameters and viewing angles. These signals are rather weak and hardly detectable within the large error box (similar to 100 deg(2)) of a gravitational wave trigger. A second electromagnetic transient results from neutrino-driven winds. These winds produce 'weak' r-process material with 50 < A < 130 and abundance patterns that vary substantially between different merger cases. For an adopted opacity of 1 cm(2) g(-1), the resulting transients peak in the UV/optical about 6 h after the merger with a luminosity of approximate to 10(41) erg s(-1) (for a wind of 0.01 M-circle dot) These signals are marginally detectable in deep follow-up searches (e. g. using Hypersuprime camera on Subaru). A subsequent detection of the weaker but longer lasting IR signal would allow an identification of the merger event. We briefly discuss the implications of our results to the recent detection of a near infrared (nIR) transient accompanying GRB 130603B.

  • 28. Kasliwal, M. M.
    et al.
    Kasen, D.
    Lau, R. M.
    Perley, D. A.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ofek, E. O.
    Hotokezaka, K.
    Chary, R.-R.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kaplan, D. L.
    Spitzer mid-infrared detections of neutron star merger GW170817 suggests synthesis of the heaviest elements2022In: Monthly Notices of the Royal Astronomical Society: Letters, ISSN 1745-3925, Vol. 510, no 1, p. L7-L12Article in journal (Refereed)
    Abstract [en]

    We report our Spitzer Space Telescope observations and detections of the binary neutron star merger GW170817. At 4.5 μm, GW170817 is detected at 21.9 mag AB at +43 days and 23.9 mag AB at +74 days after merger. At 3.6 μm, GW170817 is not detected to a limit of 23.2 mag AB at +43 days and 23.1 mag AB at +74 days. Our detections constitute the latest and reddest constraints on the kilonova/macronova emission and composition of heavy elements. The 4.5 μm luminosity at this late phase cannot be explained by elements exclusively from the first abundance peak of the r-process. Moreover, the steep decline in the Spitzer band, with a power-law index of 3.4 ± 0.2, can be explained by a few of the heaviest isotopes with half-life around 14 d dominating the luminosity (e.g. 140Ba, 143Pr, 147Nd, 156Eu, 191Os, 223Ra, 225Ra, 233Pa, 234Th) or a model with lower deposition efficiency. This data offers evidence that the heaviest elements in the second and third r-process abundance peak were indeed synthesized. Our conclusion is verified by both analytics and network simulations and robust despite intricacies and uncertainties in the nuclear physics. Future observations with Spitzer and James Webb Space Telescope will further illuminate the relative abundance of the synthesized heavy elements.

  • 29. Kasliwal, M. M.
    et al.
    Nakar, E.
    Singer, L. P.
    Kaplan, D. L.
    Cook, D. O.
    Van Sistine, A.
    Lau, R. M.
    Fremling, C.
    Gottlieb, O.
    Jencson, J. E.
    Adams, S. M.
    Feindt, Ulrich
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hotokezaka, K.
    Ghosh, S.
    Perley, D. A.
    Yu, P-C.
    Piran, T.
    Allison, J. R.
    Anupama, G. C.
    Balasubramanian, A.
    Bannister, K. W.
    Bally, J.
    Barnes, J.
    Barway, S.
    Bellm, E.
    Bhalerao, V.
    Bhattacharya, D.
    Blagorodnova, N.
    Bloom, J. S.
    Brady, P. R.
    Cannella, C.
    Chatterjee, D.
    Cenko, S. B.
    Cobb, B. E.
    Copperwheat, C.
    Corsi, A.
    De, K.
    Dobie, D.
    Emery, S. W. K.
    Evans, P. A.
    Fox, O. D.
    Frail, D. A.
    Frohmaier, C.
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hallinan, G.
    Harrison, F.
    Helou, G.
    Hinderer, T.
    Ho, A. Y. Q.
    Horesh, A.
    Ip, W-H.
    Itoh, R.
    Kasen, D.
    Kim, H.
    Kuin, N. P. M.
    Kupfer, T.
    Lynch, C.
    Madsen, K.
    Mazzali, P. A.
    Miller, A. A.
    Mooley, K.
    Murphy, T.
    Ngeow, C-C.
    Nichols, D.
    Nissanke, S.
    Nugent, P.
    Ofek, E. O.
    Qi, H.
    Quimby, R. M.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Rusu, F.
    Sadler, E. M.
    Schmidt, P.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Steele, I.
    Williamson, A. R.
    Xu, Y.
    Yan, L.
    Yatsu, Y.
    Zhang, C.
    Zhao, W.
    Illuminating gravitational waves: A concordant picture of photons from a neutron star merger2017In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 358, no 6370, p. 1559-+Article in journal (Refereed)
    Abstract [en]

    Merging neutron stars offer an excellent laboratory for simultaneously studying strong-field gravity and matter in extreme environments. We establish the physical association of an electromagnetic counterpart (EM170817) with gravitational waves (GW170817) detected from merging neutron stars. By synthesizing a panchromatic data set, we demonstrate that merging neutron stars are a long-sought production site forging heavy elements by r-process nucleosynthesis. The weak gamma rays seen in EM170817 are dissimilar to classical short gamma-ray bursts with ultrarelativistic jets. Instead, we suggest that breakout of a wide-angle, mildly relativistic cocoon engulfing the jet explains the low-luminosity gamma rays, the high-luminosity ultraviolet-optical-infrared, and the delayed radio and x-ray emission. We posit that all neutron star mergers may lead to a wide-angle cocoon breakout, sometimes accompanied by a successful jet and sometimes by a choked jet.

  • 30. Korobkin, O.
    et al.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Arcones, A.
    Winteler, C.
    On the astrophysical robustness of the neutron star merger r process2012In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 426, no 3, p. 1940-1949Article in journal (Refereed)
    Abstract [en]

    In this study we explore nucleosynthesis in the dynamic ejecta of compact binary mergers. We are particularly interested in the question how sensitive the resulting abundance patterns are to the parameters of the merging system. Therefore, we systematically investigate combinations of neutron star masses in the range from 1.0 to 2.0 M? and, for completeness, we compare the results with those from two simulations of a neutron star black hole merger. The ejecta masses vary by a factor of 5 for the studied systems, but all amounts are (within the uncertainties of the merger rates) compatible with being a major source of the cosmic r-process. The ejecta undergo robust r-process nucleosynthesis which produces all the elements from the second to the third peak in close-to-solar ratios. Most strikingly, this r-process is extremely robust, and all 23 investigated binary systems yield practically identical abundance patterns. This is mainly the result of the ejecta being extremely neutron rich (Ye similar to 0.04) and the r-process path meandering along the neutron drip line so that the abundances are determined entirely by nuclear rather than astrophysical properties. While further questions related to galactic chemical evolution need to be explored in future studies, we consider this robustness together with the ease with which both the second and third peak are reproduced as strong indications that compact binary mergers are prime candidates for the sources of the observed unique heavy r-process component.

  • 31.
    Korobkin, Oleg
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Abdikamalov, E.
    Stergioulas, N.
    Schnetter, E.
    Zink, B.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ott, C. D.
    The runaway instability in general relativistic accretion discs2013In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 431, no 1, p. 349-354Article in journal (Refereed)
    Abstract [en]

    When an accretion disc falls prey to the runaway instability, a large portion of its mass is devoured by the black hole within a few dynamical times. Despite decades of effort, it is still unclear under what conditions such an instability can occur. The technically most advanced relativistic simulations to date were unable to find a clear sign for the onset of the instability. In this work, we present three-dimensional relativistic hydrodynamics simulations of accretion discs around black holes in dynamical space-time. We focus on the configurations that are expected to be particularly prone to the development of this instability. We demonstrate, for the first time, that the fully self-consistent general relativistic evolution does indeed produce a runaway instability.

  • 32. Korobkin, Oleg
    et al.
    Wollaeger, Ryan T.
    Fryer, Christopher L.
    Hungerford, Aimee L.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fontes, Christopher J.
    Mumpower, Matthew R.
    Chase, Eve A.
    Even, Wesley P.
    Miller, Jonah
    Misch, G. Wendell
    Lippuner, Jonas
    Axisymmetric Radiative Transfer Models of Kilonovae2021In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 910, no 2, article id 116Article in journal (Refereed)
    Abstract [en]

    The detailed observations of GW170817 proved for the first time directly that neutron star mergers are a major production site of heavy elements. The observations could be fit by a number of simulations that qualitatively agree, but can quantitatively differ (e.g., in total r-process mass) by an order of magnitude. We categorize kilonova ejecta into several typical morphologies motivated by numerical simulations, and apply a radiative transfer Monte Carlo code to study how the geometric distribution of the ejecta shapes the emitted radiation. We find major impacts on both spectra and light curves. The peak bolometric luminosity can vary by two orders of magnitude and the timing of its peak by a factor of five. These findings provide the crucial implication that the ejecta masses inferred from observations around the peak brightness are uncertain by at least an order of magnitude. Mixed two-component models with lanthanide-rich ejecta are particularly sensitive to geometric distribution. A subset of mixed models shows very strong viewing angle dependence due to lanthanide curtaining, which persists even if the relative mass of lanthanide-rich component is small. The angular dependence is weak in the rest of our models, but different geometric combinations of the two components lead to a highly diverse set of light curves. We identify geometry-dependent P Cygni features in late spectra that directly map out strong lines in the simulated opacity of neodymium, which can help to constrain the ejecta geometry and to directly probe the r-process abundances.

  • 33. Lamb, Gavin P.
    et al.
    Nativi, Lorenzo
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University of Hamburg, Germany.
    Kann, D. Alexander
    Levan, Andrew
    Lundman, Christoffer
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Tanvir, Nial
    Inhomogeneous Jets from Neutron Star Mergers: One Jet to Rule Them All2022In: Universe, E-ISSN 2218-1997, Vol. 8, no 12, article id 612Article in journal (Refereed)
    Abstract [en]

    Using the resultant profiles from 3D hydrodynamic simulations of relativistic jets interacting with neutron star merger wind ejecta, we show how the inhomogeneity of energy and velocity across the jet surface profile can alter the observed afterglow lightcurve. We find that the peak afterglow flux depends sensitively on the observer’s line-of-sight, not only via the jet inclination but also through the jet rotation: for an observer viewing the afterglow within the GRB-bright jet core, we find a peak flux variability on the order <0.50.5 dex through rotational orientation and <1.31.3 dex for the polar inclination. An observed afterglow’s peak flux can be used to infer the jet kinetic energy, and where a top-hat jet is assumed, we find the range of inferred jet kinetic energies for our various model afterglow lightcurves (with fixed model parameters), covers ∼1/3 of the observed short GRB population. Additionally, we present an analytic jet structure function that includes physically motivated parameter uncertainties due to variability through the rotation of the source. An approximation for the change in collimation due to the merger ejecta mass is included and we show that by considering the observed range of merger ejecta masses from short GRB kilonova candidates, a population of merger jets with a fixed intrinsic jet energy is capable of explaining the observed broad diversity seen in short GRB afterglows.

  • 34. Lamb, Gavin Paul
    et al.
    Nativi, Lorenzo
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kann, D. Alexander
    Levan, Andrew
    Lundman, Christoffer
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Tanvir, Nial
    Inhomogeneous Jets from Neutron Star Mergers: One Jet to Rule them all2021In: MNRASArticle in journal (Other academic)
    Abstract [en]

    The broad, ∼4 order of magnitude range in energy, inferred via afterglow observations, for the short Gamma-Ray Burst (GRB) population is difficult to reconcile with the narrow energy distribution expected from neutron star merger progenitors. Using the resultant profiles from 3D hydrodynamic simulations of relativistic jets interacting with neutron star merger wind ejecta, we show how the inhomogeneity of energy and velocity can alter the observed afterglow lightcurve. From a single jet we find that the peak afterglow flux depends sensitively on the observer's line-of-sight: at an inclination within the GRB emitting region we find peak flux variability on the order <0.5 dex through rotational orientation, and <1.3 dex for polar inclination. The inferred jet kinetic energy for a fixed parameter afterglow covers ∼1/3 of the observed short GRB population. We find a physically motivated, analytic jet structure function via our simulations and include an approximation for the varying collimation due to the merger ejecta mass. We show that by considering the observed range of merger ejecta masses, a short GRB jet population with a single intrinsic energy is capable of explaining the observed broad diversity in short GRB kinetic energies.

    Download full text (pdf)
    fulltext
  • 35. Levan, A. J.
    et al.
    Lyman, J. D.
    Tanvir, N. R.
    Hjorth, J.
    Mandel, I.
    Stanway, E. R.
    Steeghs, D.
    Fruchter, A. S.
    Troja, E.
    Schrøder, S. L.
    Wiersema, K.
    Bruun, S. H.
    Cano, Z.
    Cenko, S. B.
    de Ugarte Postigo, A.
    Evans, P.
    Fairhurst, S.
    Fox, O. D.
    Fynbo, J. P. U.
    Gompertz, B.
    Greiner, J.
    Im, M.
    Izzo, L.
    Jakobsson, P.
    Kangas, T.
    Khandrika, H. G.
    Lien, A. Y.
    Malesani, D.
    O'Brien, P.
    Osborne, J. P.
    Palazzi, E.
    Pian, E.
    Perley, D. A.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ryan, R. E.
    Schulze, S.
    Sutton, P.
    Thöne, C. C.
    Watson, D. J.
    Wijers, R. A. M. J.
    The Environment of the Binary Neutron Star Merger GW1708172017In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 848, no 2, article id L28Article in journal (Refereed)
    Abstract [en]

    We present Hubble Space Telescope (HST) and Chandra imaging, combined with Very Large Telescope MUSE integral field spectroscopy of the counterpart and host galaxy of the first binary neutron star merger detected via gravitational-wave emission by LIGO and Virgo, GW170817. The host galaxy, NGC 4993, is an S0 galaxy at z - 0.009783. There is evidence for large, face-on spiral shells in continuum imaging, and edge-on spiral features visible in nebular emission lines. This suggests that NGC 4993 has undergone a relatively recent (less than or similar to 1 Gyr) dry merger. This merger may provide the fuel for a weak active nucleus seen in Chandra imaging. At the location of the counterpart, HST imaging implies there is no globular or young stellar cluster, with a limit of a few thousand solar masses for any young system. The population in the vicinity is predominantly old with less than or similar to 1% of any light arising from a population with ages <500 Myr. Both the host galaxy properties and those of the transient location are consistent with the distributions seen for short-duration gamma-ray bursts, although the source position lies well within the effective radius (r(e) similar to 3 kpc), providing an r(e)-normalized offset that is closer than similar to 90% of short GRBs. For the long delay time implied by the stellar population, this suggests that the kick velocity was significantly less than the galaxy escape velocity. We do not see any narrow host galaxy interstellar medium features within the counterpart spectrum, implying low extinction, and that the binary may lie in front of the bulk of the host galaxy.

  • 36. Lyman, J. D.
    et al.
    Lamb, G. P.
    Levan, A. J.
    Mandel, I.
    Tanvir, N. R.
    Kobayashi, S.
    Gompertz, B.
    Hjorth, J.
    Fruchter, A. S.
    Kangas, T.
    Steeghs, D.
    Steele, I. A.
    Cano, Z.
    Copperwheat, C.
    Evans, P. A.
    Fynbo, J. P. U.
    Gall, C.
    Im, M.
    Izzo, L.
    Jakobsson, P.
    Milvang-Jensen, B.
    O'Brien, P.
    Osborne, J. P.
    Palazzi, E.
    Perley, D. A.
    Pian, E.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Rowlinson, A.
    Schulze, S.
    Stanway, E. R.
    Sutton, P.
    Thöne, C. C.
    de Ugarte Postigo, A.
    Watson, D. J.
    Wiersema, K.
    Wijers, R. A. M. J.
    The optical afterglow of the short gamma-ray burst associated with GW1708172018In: Nature Astronomy, E-ISSN 2397-3366, Vol. 2, no 9, p. 751-754Article in journal (Refereed)
    Abstract [en]

    The binary neutron star merger GW170817 was the first multi-messenger event observed in both gravitational and electromagnetic waves(1,2). The electromagnetic signal began approximately two seconds post-merger with a weak, short burst of gamma rays(3), which was followed over the next hours and days by the ultraviolet, optical and near-infrared emission from a radioactively powered kilonova(4-11). Later, non-thermal rising X-ray and radio emission was observed(12,13). The low luminosity of the gamma rays and the rising non-thermal flux from the source at late times could indicate that we are outside the opening angle of the beamed relativistic jet. Alternatively, the emission could be arising from a cocoon of material formed from the interaction between a jet and the merger ejecta(13-15). Here we present late-time optical detections and deep near-infrared limits on the emission from GW170817 at 110 days post-merger. Our new observations are at odds with expectations of late-time emission from kilonova models, being too bright and blue(16,17). Instead, the emission arises from the interaction between the relativistic ejecta of GW170817 and the interstellar medium. We show that this emission matches the expectations of a Gaussian-structured relativistic jet, which would have launched a high-luminosity, short gamma-ray burst to an aligned observer. However, other jet structure or cocoon models can also match current data-the future evolution of the afterglow will directly distinguish the origin of the emission.

  • 37. MacLeod, Morgan
    et al.
    Guillochon, James
    Ramirez-Ruiz, Enrico
    Kasen, Daniel
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    OPTICAL THERMONUCLEAR TRANSIENTS FROM TIDAL COMPRESSION OF WHITE DWARFS AS TRACERS OF THE LOW END OF THE MASSIVE BLACK HOLE MASS FUNCTION2016In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 819, no 1, article id 3Article in journal (Refereed)
    Abstract [en]

    In this paper, we model the observable signatures of tidal disruptions of white dwarf (WD) stars using massive black holes (MBHs) of moderate mass, approximate to 10(3)-10(5) M-circle dot. When the WD passes deep enough within the MBH's tidal field, these signatures include thermonuclear transients from burning during maximum compression. We combine a hydrodynamic simulation that includes nuclear burning of the disruption of a 0.6 M-circle dot C/O WD with a Monte Carlo radiative transfer calculation to synthesize the properties of a representative transient. The transient's emission emerges in the optical, with light. curves and spectra reminiscent of Type I supernovae. The properties are strongly viewing. angle dependent, and key spectral signatures are approximate to 10,000 km s(-1) doppler shifts, due to the orbital motion of the unbound ejecta. Disruptions of He WDs likely produce large quantities of intermediate-mass elements, offering a possible production mechanism for Ca-rich transients. Accompanying multi-wavelength transients are fueled by accretion and arise from the nascent accretion disk and relativistic jet. If MBHs of moderate mass exist with number densities similar to those of supermassive BHs, both high-energy wide-field monitors and upcoming optical surveys should detect tens to hundreds of WD tidal disruptions per year. The current best strategy for their detection may therefore be deep optical follow-up of high-energy transients of unusually long duration. The detection rate or the nondetection of these transients by current and upcoming surveys can thus be used to place meaningful constraints on the extrapolation of the MBH mass function to moderate masses.

  • 38. Maguire, Kate
    et al.
    Eracleous, Michael
    Jonker, Peter G.
    MacLeod, Morgan
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Tidal Disruptions of White Dwarfs: Theoretical Models and Observational Prospects2020In: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 216, no 3, article id 39Article, review/survey (Refereed)
    Abstract [en]

    White dwarf stars that enter the tidal radius of black holes with masses less than or similar to 10(5) M-circle dot are doomed to be ripped apart by tidal forces. Black holes in this mass range between stellar black holes and supermassive black holes have not been conclusively identified so the detection of a tidal disruption of a white dwarf would provide clear evidence for the existence of intermediate-mass black holes. In this review, we present a theoretical and observational overview of the transient events that result from the tidal disruptions of white dwarfs by intermediate-mass black holes. This includes discussion of the latest simulations and predicted properties, the results of observational searches, as well as a summary of the potential for gravitational wave emission to be detected with upcoming missions.

  • 39. Martin, D.
    et al.
    Perego, A.
    Arcones, A.
    Thielemann, F. -K.
    Korobkin, Oleg
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Astronomy.
    NEUTRINO-DRIVEN WINDS IN THE AFTERMATH OF A NEUTRON STAR MERGER: NUCLEOSYNTHESIS AND ELECTROMAGNETIC TRANSIENTS2015In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 813, no 1, article id 2Article in journal (Refereed)
    Abstract [en]

    We present a comprehensive nucleosynthesis study of the neutrino-driven wind in the aftermath of a binary neutron star merger. Our focus is the initial remnant phase when a massive central neutron star is present. Using tracers from a recent hydrodynamical simulation, we determine total masses and integrated abundances to characterize the composition of unbound matter. We find that the nucleosynthetic yields depend sensitively on both the life time of the massive neutron star and the polar angle. Matter in excess of up to 9 x 10(-3) M-circle dot becomes unbound until similar to 200 ms. Due to electron fractions of Y-e approximate to 0.2-0.4, mainly nuclei with mass numbers A < 130 are synthesized, complementing the yields from the earlier dynamic ejecta. Mixing scenarios with these two types of ejecta can explain the abundance pattern in r-process enriched metal-poor stars. Additionally, we calculate heating rates for the decay of the freshly produced radioactive isotopes. The resulting light curve peaks in the blue band after about 4 hr. Furthermore, high opacities due to heavy r-process nuclei in the dynamic ejecta lead to a second peak in the infrared after 3-4 days.

  • 40. Matteucci, F.
    et al.
    Romano, D.
    Arcones, A.
    Korobkin, Oleg
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Europium production: neutron star mergers versus core-collapse supernovae2014In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 438, no 3, p. 2177-2185Article in journal (Refereed)
    Abstract [en]

    We have explored the Eu production in the Milky Way by means of a very detailed chemical evolution model. In particular, we have assumed that Eu is formed in merging neutron star (or neutron star-black hole) binaries as well as in Type II supernovae. We have tested the effects of several important parameters influencing the production of Eu during the merging of two neutron stars, such as (i) the time-scale of coalescence, (ii) the Eu yields and (iii) the range of initial masses for the progenitors of the neutron stars. The yields of Eu from Type II supernovae are very uncertain, more than those from coalescing neutron stars, so we have explored several possibilities. We have compared our model results with the observed rate of coalescence of neutron stars, the solar Eu abundance, the [Eu/Fe] versus [Fe/H] relation in the solar vicinity and the [Eu/H] gradient along the Galactic disc. Our main results can be summarized as follows: (i) neutron star mergers can be entirely responsible for the production of Eu in the Galaxy if the coalescence time-scale is no longer than 1 Myr for the bulk of binary systems, the Eu yield is around 3 x 10(-7) M-circle dot and the mass range of progenitors of neutron stars is 9-50 M-circle dot; (ii) both Type II supernovae and merging neutron stars can produce the right amount of Eu if the neutron star mergers produce 2 x 10(-7) M-circle dot per system and Type II supernovae, with progenitors in the range 20-50 M-circle dot, produce yields of Eu of the order of 10(-8)-10(-9) M-circle dot; (iii) either models with only neutron stars producing Eu or mixed ones can reproduce the observed Eu abundance gradient along the Galactic disc.

  • 41. Murguia-Berthier, Ariadna
    et al.
    Ramirez-Ruiz, Enrico
    Colle, Fabio De
    Janiuk, Agnieszka
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Lee, William H.
    The Fate of the Merger Remnant in GW170817 and Its Imprint on the Jet Structure2021In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 908, no 2, article id 152Article in journal (Refereed)
    Abstract [en]

    The first neutron star binary merger detected in gravitational waves, GW170817, and the subsequent detection of its emission across the electromagnetic spectrum showed that these systems are viable progenitors of short γ-ray bursts (sGRB). The afterglow signal of GW170817 has been found to be consistent with a structured GRB jet seen off-axis, requiring significant amounts of relativistic material at large angles. This trait can be attributed to the interaction of the relativistic jet with the external wind medium. Here we perform numerical simulations of relativistic jets interacting with realistic wind environments in order to explore how the properties of the wind and central engine affect the structure of successful jets. We find that the angular energy distribution of the jet depends primarily on the ratio between the lifetime of the jet and the time it takes the merger remnant to collapse. We make use of these simulations to constrain the time it took for the merger remnant in GW170817 to collapse into a black hole based on the angular structure of the jet as inferred from afterglow observations. We conclude that the lifetime of the merger remnant in GW170817 was ≈1–1.7 s, which, after collapse, triggered the formation of the jet.

  • 42. Murguia-Berthier, Ariadna
    et al.
    Ramirez-Ruiz, Enrico
    Montes, Gabriela
    De Colle, Fabio
    Rezzolla, Luciano
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Takami, Kentaro
    Perego, Albino
    Lee, William H.
    The Properties of Short Gamma-Ray Burst Jets Triggered by Neutron Star Mergers2017In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 835, no 2, article id L34Article in journal (Refereed)
    Abstract [en]

    The most popular model for short gamma-ray bursts (sGRBs) involves the coalescence of binary neutron stars. Because the progenitor is actually hidden from view, we must consider under which circumstances such merging systems are capable of producing a successful sGRB. Soon after coalescence, winds are launched from the merger remnant. In this paper, we use realistic wind profiles derived from global merger simulations in order to investigate the interaction of sGRB jets with these winds using numerical simulations. We analyze the conditions for which these axisymmetric winds permit relativistic jets to break out and produce an sGRB. We find that jets with luminosities comparable to those observed in sGRBs are only successful when their half-opening angles are below approximate to 20 degrees. This jet collimation mechanism leads to a simple physical interpretation of the luminosities and opening angles inferred for sGRBs. If wide, low-luminosity jets are observed, they might be indicative of a different progenitor avenue such as the merger of a neutron star with a black hole. We also use the observed durations of sGRB to place constraints on the lifetime of the wind phase, which is determined by the time it takes the jet to break out. In all cases we find that the derived limits argue against completely stable remnants for binary neutron star mergers that produce sGRBs.

  • 43.
    Nativi, Lorenzo
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bulla, Mattia
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Lundman, Christoffer
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kowal, G.
    Gizzi, Davide
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Lamb, G. P.
    Perego, A.
    Can jets make the radioactively powered emission from neutron star mergers bluer?2021In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 500, no 2, p. 1772-1783Article in journal (Refereed)
    Abstract [en]

    Neutron star mergers eject neutron-rich matter in which heavy elements are synthesized. The decay of these freshly synthesized elements powers electromagnetic transients ('macronovae' or 'kilonovae') whose luminosity and colour strongly depend on their nuclear composition. If the ejecta are very neutron-rich (electron fraction Y-e < 0.25), they contain fair amounts of lanthanides and actinides that have large opacities and therefore efficiently trap the radiation inside the ejecta so that the emission peaks in the red part of the spectrum. Even small amounts of this high-opacity material can obscure emission from lower lying material and therefore act as a 'lanthanide curtain'. Here, we investigate how a relativistic jet that punches through the ejecta can potentially push away a significant fraction of the high opacity material before the macronova begins to shine. We use the results of detailed neutrino-driven wind studies as initial conditions and explore with 3D special relativistic hydrodynamic simulations how jets are propagating through these winds. Subsequently, we perform Monte Carlo radiative transfer calculations to explore the resulting macronova emission. We find that the hole punched by the jet makes the macronova brighter and bluer for on-axis observers during the first few days of emission, and that more powerful jets have larger impacts on the macronova.

  • 44.
    Nativi, Lorenzo
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Lamb, G. P.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Lundman, Christoffer
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kowal, G.
    Are interactions with neutron star merger winds shaping the jets?2022In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 509, no 1, p. 903-913Article in journal (Refereed)
    Abstract [en]

    Jets can become collimated as they propagate through dense environments and understanding such interactions is crucial for linking physical models of the environments to observations. In this work, we use 3D special-relativistic simulations to study how jets propagate through the environment created around a neutron star merger remnant by neutrino-driven winds. We simulate four jets with two different initial structures, top-hat and Gaussian, and two luminosities. After jet breakout, we study the angular jet structures and the resulting afterglow light curves. We find that the initial angular structures are efficiently washed out during the propagation, despite the small wind mass of only ∼10−3 M. The final structure depends on the jet luminosity as less energetic jets are more strongly collimated, and entrainment of baryons leads to a moderate outflow Lorentz factor (≈40). Although ourjets are not specifically intended to model the outflows of the GW170817 event, we show that they can be used to produce light curves consistent with the afterglow observed in the aftermath of GW170817. Using this procedure, we show how the inferred physical parameters e.g. inclination angle, ambient particle number density, can vary substantially between independent fits of the same dataset, and appear to be sensitive to smaller details of the angular jet shape, indicating that observationally inferred parameters may depend sensitively on the employed jet models.

  • 45. Neuweiler, Anna
    et al.
    Dietrich, Tim
    Bulla, Mattia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University of Ferrara, Italy.
    Chaurasia, Swami Vivekanandji
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Sternwarte Hamburg, Germany.
    Ujevic, Maximiliano
    Long-term simulations of dynamical ejecta: Homologous expansion and kilonova properties2023In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 107, no 2, article id 023016Article in journal (Refereed)
    Abstract [en]

    Accurate numerical-relativity simulations are essential to study the rich phenomenology of binary neutron star systems. In this work, we focus on the material that is dynamically ejected during the merger process and on the kilonova transient it produces. Typically, radiative transfer simulations of kilonova light curves from ejecta make the assumption of homologous expansion, but this condition might not always be met at the end of usually very short numerical-relativity simulations. In this article, we adjust the infrastructure of the bam code to enable longer simulations of the dynamical ejecta with the aim of investigating when the condition of homologous expansion is satisfied. In fact, we observe that the deviations from a perfect homologous expansion are about ≲ 30% at roughly 100 ms after the merger. While the calculation of the kilonova light curves is affected by the resolution as well as our method of simplifying the ejecta simulation, these deviations from the homologous expansion also bias the results. We determine this influence by extracting the ejecta data for different reference times and use them as input to radiative transfer simulations. Our results show that the light curves for extraction times later than 80 ms after the merger deviate by ≲ 0.4  mag and are mostly consistent with numerical noise. Accordingly, deviations from the homologous expansion for the dynamical ejecta component are negligible from ∼ 80  ms for the purpose of kilonova modeling.

  • 46. Perego, A.
    et al.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy.
    Cabezón, R. M.
    Korobkin, Oleg
    Stockholm University, Faculty of Science, Department of Astronomy.
    Käppeli, R.
    Arcones, A.
    Liebendörfer, M.
    Neutrino-driven winds from neutron star merger remnants2014In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 443, no 4, p. 3134-3156Article in journal (Refereed)
    Abstract [en]

    We present a detailed, three-dimensional hydrodynamic study of the neutrino-driven winds emerging from the remnant of a neutron star merger. Our simulations are performed with the Newtonian, Eulerian code FISH, augmented by a detailed, spectral neutrino leakage scheme that accounts for neutrino absorption. Consistent with earlier two-dimensional studies, a strong baryonic wind is blown out along the original binary rotation axis within approximate to 100 ms. From this model, we compute a lower limit on the expelled mass of 3.5 x 10(-3) M-circle dot, relevant for heavy element nucleosynthesis. Because of stronger neutrino irradiation, the polar regions show substantially larger electron fractions than those at lower latitudes. The polar ejecta produce interesting r-process contributions from A approximate to 80 to about 130, while the more neutron-rich, lower latitude parts produce elements up to the third r-process peak near A approximate to 195. We calculate the properties of electromagnetic transients powered by the radioactivity in the wind, in addition to the 'macronova' transient stemming from the dynamic ejecta. The polar regions produce ultraviolet/optical transients reaching luminosities up to 10(41) erg s(-1), which peak around 1 d in optical and 0.3 d in bolometric luminosity. The lower latitude regions, due to their contamination with high-opacity heavy elements, produce dimmer and more red signals, peaking after similar to 2 d in optical and infrared.

  • 47. Perego, Albino
    et al.
    Gafton, Emanuel
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Cabezon, Ruben
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Liebendoerfer, Matthias
    MODA: a new algorithm to compute optical depths in multidimensional hydrodynamic simulations2014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 568, p. A11-Article in journal (Refereed)
    Abstract [en]

    Aims, We introduce the multidimensional optical depth algorithm (MODA) for the calculation of optical depths in approximate multidimensional radiative transport schemes, equally applicable to neutrinos and photons. Motivated by (but not limited to) neutrino transport in three-dimensional simulations of core-collapse supernovae and neutron star mergers. our method makes no assumptions about the geometry of the matter distribution, apart from expecting optically transparent boundaries. Methods. Based on local information about opacities, the algorithm figures out an escape route that tends to minimize the optical depth without assuming any predefined paths for radiation. Its adaptivity makes it suitable for a variety of astrophysical settings with complicated geometry (e.g., core-collapse supernovae, compact baldly mergers, tidal disruptions, star formation, etc.). We implement the MODA algorithm into both a Eulerian hydrodynamics code with a fixed, uniform grid and into an SPH code where we use a tree structure that is otherwise used for searching neighbors and calculating gravity. Results. In a series of numerical experiments, we compare the MODA results with analytically known solutions. We also use snapshots from actual 3D simulations and compare the results of MODA with those obtained with other methods, such as the global and local ray-by-ray method. It turns out that MODA achieves excellent accuracy at a moderate computational cost In appendix we also discuss implementation details and parallelization strategies.

  • 48. Piran, Tsvi
    et al.
    Nakar, Ehud
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy.
    The electromagnetic signals of compact binary mergers2013In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 430, no 3, p. 2121-2136Article in journal (Refereed)
    Abstract [en]

    Compact binary mergers are prime sources of gravitational waves (GWs), targeted by current and next generation detectors. The question 'what is the observable electromagnetic (EM) signature of a compact binary merger?' is an intriguing one with crucial consequences to the quest for GWs. We present a large set of numerical simulations that focus on the EM signals that emerge from the dynamically ejected subrelativistic material. These outflows produce on a time-scale of a day macronovae - short-lived infrared (IR) to ultraviolet (UV) signals powered by radioactive decay. Like in regular supernovae the interaction of this outflow with the surrounding matter inevitably leads to a long-lasting remnant. We calculate the expected radio signals of these remnants on time-scales longer than a year, when the subrelativistic ejecta dominate the emission. We discuss their detectability in 1.4 GHz and 150 MHz and compare it with an updated estimate of the detectability of short gamma-ray bursts' orphan afterglows (which are produced by a different component of this outflow). We find that mergers with characteristics similar to those of the Galactic neutron star binary population (similar masses and typical circummerger Galactic disc density of similar to 1 cm(-3)) that take place at the detection horizon of advanced GW detectors (300 Mpc) yield 1.4 GHz [150 MHz] signals of similar to 50 [300] mu Jy, for several years. The signal on time-scales of weeks is dominated by the mildly and/or ultrarelativistic outflow, which is not accounted for by our simulations, and is expected to be even brighter. Upcoming all sky surveys are expected to detect a few dozen, and possibly more, merger remnants at any given time thereby providing robust lower limits to the mergers rate even before the advanced GW detectors become operational. The macronovae signals from the same distance peak in the IR to UV range at an observed magnitude that may be as bright as 22-23 about 10 h after the merger but dimmer, redder and longer if the opacity is larger.

  • 49.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    A gravitational-wave standard siren measurement of the Hubble constant2017In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 551, no 7678, p. 85-88Article in journal (Refereed)
    Abstract [en]

    On 17 August 2017, the Advanced LIGO(1) and Virgo(2) detectors observed the gravitational-wave event GW170817-a strong signal from the merger of a binary neutron-star system(3). Less than two seconds after the merger, a gamma-ray burst (GRB 170817A) was detected within a region of the sky consistent with the LIGO-Virgo-derived location of the gravitational-wave source(4-6). This sky region was subsequently observed by optical astronomy facilities(7), resulting in the identification(8-13) of an optical transient signal within about ten arcseconds of the galaxy NGC 4993. This detection of GW170817 in both gravitational waves and electromagnetic waves represents the first 'multi-messenger' astronomical observation. Such observations enable GW170817 to be used as a 'standard siren'(14-18) (meaning that the absolute distance to the source can be determined directly from the gravitational-wave measurements) to measure the Hubble constant. This quantity represents the local expansion rate of the Universe, sets the overall scale of the Universe and is of fundamental importance to cosmology. Here we report a measurement of the Hubble constant that combines the distance to the source inferred purely from the gravitational-wave signal with the recession velocity inferred from measurements of the redshift using the electromagnetic data. In contrast to previous measurements, ours does not require the use of a cosmic 'distance ladder'(19): the gravitational-wave analysis can be used to estimate the luminosity distance out to cosmological scales directly, without the use of intermediate astronomical distance measurements. We determine the Hubble constant to be about 70 kilometres per second per megaparsec. This value is consistent with existing measurements(20,21), while being completely independent of them. Additional standard siren measurements from future gravitational-wave sources will enable the Hubble constant to be constrained to high precision.

  • 50.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    A Simple, Entropy-based Dissipation Trigger for SPH2020In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 898, no 1, article id 60Article in journal (Refereed)
    Abstract [en]

    Smoothed particle hydrodynamics (SPH) schemes need to be enhanced by dissipation mechanisms to handle shocks. Most SPH formulations rely on artificial viscosity and, while this works well in pure shocks, attention must be paid to avoid dissipation where it is not wanted. Commonly used approaches include limiters and time-dependent dissipation parameters. The former try to distinguish shocks from other types of flows that do not require dissipation while in the latter approach the dissipation parameters are steered by some source term (trigger) and, if not triggered, they decay to a predescribed floor value. The commonly used source terms trigger on either compression, -del . v, or its time derivative. Here we explore a novel way to trigger SPH-dissipation: since an ideal fluid conserves entropy exactly, its numerical nonconservation can be used to identify troubled particles that need dissipation because they either pass through a shock or become noisy for other reasons. Our new scheme is implemented into the Lagrangian hydrodynamics code MAGMA2 and is scrutinized in a number of shock and fluid instability tests. We find excellent results in shocks and only a very moderate (and desired) switch-on in instability tests. The new scheme is robust, trivial to implement into existing SPH codes, and does not add any computational overhead.

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