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  • 1.
    Abdollahi, S.
    et al.
    Hiroshima Univ, Dept Phys Sci, Higashihiroshima, Hiroshima 7398526, Japan..
    Ajello, M.
    Clemson Univ, Kinard Lab Phys, Dept Phys & Astron, Clemson, SC 29634 USA..
    Helgason, Kári
    KTH. Max Planck Inst Astrophys, Postfach 1317, D-85741 Garching, Germany.;Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden..
    Jóhannesson, Gudlaugur
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Univ Iceland, Sci Inst, IS-107 Reykjavik, Iceland.;Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden..
    Larsson, Stefan
    KTH, School of Engineering Sciences (SCI), Physics. AlbaNova, Oskar Klein Ctr Cosmoparticle Phys, SE-10691 Stockholm, Sweden..
    et al.,
    A gamma-ray determination of the Universe's star formation history2018In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 362, no 6418, p. 1031-+Article in journal (Refereed)
    Abstract [en]

    The light emitted by all galaxies over the history of the Universe produces the extragalactic background light (EBL) at ultraviolet, optical, and infrared wavelengths. The EBL is a source of opacity for gamma rays via photon-photon interactions, leaving an imprint in the spectra of distant gamma-ray sources. We measured this attenuation using 739 active galaxies and one gamma-ray burst detected by the Fermi Large Area Telescope. This allowed us to reconstruct the evolution of the EBL and determine the star formation history of the Universe over 90% of cosmic time. Our star formation history is consistent with independent measurements from galaxy surveys, peaking at redshift z similar to 2. Upper limits of the EBL at the epoch of reionization suggest a turnover in the abundance of faint galaxies at z similar to 6.

  • 2.
    Abdollahi, S.
    et al.
    Hiroshima Univ, Dept Phys Sci, Higashihiroshima, Hiroshima 7398526, Japan..
    Axelsson, Magnus
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Stockholm Univ, Dept Phys, AlbaNova, SE-10691 Stockholm, Sweden..
    Jóhannesson, Gudlaugur
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Univ Iceland, Sci Inst, IS-107 Reykjavik, Iceland.;Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden..
    Larsson, Stefan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. AlbaNova, Oskar Klein Ctr Cosmoparticle Phys, SE-10691 Stockholm, Sweden.;Dalarna Univ, Sch Educ Hlth & Social Studies, Nat Sci, SE-79188 Falun, Sweden..
    Zaharijas, G.
    Ist Nazl Fis Nucl, Sez Trieste, I-34127 Trieste, Italy.;Univ Trieste, I-34127 Trieste, Italy.;Univ Nova Gorica, Ctr Astrophys & Cosmol, Nova Gorica, Slovenia..
    et al.,
    Fermi Large Area Telescope Fourth Source Catalog2020In: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 247, no 1, article id 33Article in journal (Refereed)
    Abstract [en]

    We present the fourth Fermi Large Area Telescope catalog (4FGL) of gamma-ray sources. Based on the first eight years of science data from the Fermi Gamma-ray Space Telescope mission in the energy range from 50 MeV to 1 TeV, it is the deepest yet in this energy range. Relative to the 3FGL catalog, the 4FGL catalog has twice as much exposure as well as a number of analysis improvements, including an updated model for the Galactic diffuse gamma-ray emission, and two sets of light curves (one-year and two-month intervals). The 4FGL catalog includes 5064 sources above 4 sigma significance, for which we provide localization and spectral properties. Seventy-five sources are modeled explicitly as spatially extended, and overall, 358 sources are considered as identified based on angular extent, periodicity, or correlated variability observed at other wavelengths. For 1336 sources, we have not found plausible counterparts at other wavelengths. More than 3130 of the identified or associated sources are active galaxies of the blazar class, and 239 are pulsars.

  • 3.
    Abergel, David
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden.
    Excitonic condensation in spatially separated one-dimensional systems2015In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 106, no 21, article id 213103Article in journal (Refereed)
    Abstract [en]

    We show theoretically that excitons can form from spatially separated one-dimensional ground state populations of electrons and holes, and that the resulting excitons can form a quasicondensate. We describe a mean-field Bardeen-Cooper-Schrieffer theory in the low carrier density regime and then focus on the core-shell nanowire giving estimates of the size of the excitonic gap for InAs/GaSb wires and as a function of all the experimentally relevant parameters. We find that optimal conditions for pairing include small overlap of the electron and hole bands, large effective mass of the carriers, and low dielectric constant of the surrounding media. Therefore, one-dimensional systems provide an attractive platform for the experimental detection of excitonic quasicondensation in zero magnetic field.

  • 4.
    Abergel, David
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Edge, Jonathan M.
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    The role of spin-orbit coupling in topologically protected interface states in Dirac materials2014In: New Journal of Physics, E-ISSN 1367-2630, Vol. 16, p. 065012-Article in journal (Refereed)
    Abstract [en]

    We highlight the fact that two-dimensional (2D) materials with Dirac-like low energy band structures and spin-orbit coupling (SOC) will produce linearly dispersing topologically protected Jackiw-Rebbi modes at interfaces where the Dirac mass changes sign. These modes may support persistent spin or valley currents parallel to the interface, and the exact arrangement of such topologically protected currents depends crucially on the details of the SOC in the material. As examples, we discuss buckled 2D hexagonal lattices such as silicene or germanene, and transition metal dichalcogenides such as MoS2.

  • 5.
    Abergel, David
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Mucha-Kruczynski, Marcin
    Infrared absorption of closely aligned heterostructures of monolayer and bilayer graphene with hexagonal boron nitride2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 11, article id 115430Article in journal (Refereed)
    Abstract [en]

    We model optical absorption of monolayer and bilayer graphene on hexagonal boron nitride for the case of closely aligned crystal lattices. We show that perturbations with different spatial symmetry can lead to similar absorption spectra. We suggest that a study of the absorption spectra as a function of the doping for an almost completely full first miniband is necessary to extract meaningful information about the moire characteristics from optical absorption measurements and to distinguish between various theoretical proposals for the physically realistic interaction. Also, for bilayer graphene, the ability to compare spectra for the opposite signs of electric-field-induced interlayer asymmetry might provide additional information about the moire parameters.

  • 6.
    Abergel, David S. L.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Center for Quantum Materials, Sweden.
    Robustness of topologically protected transport in graphene-boron nitride lateral heterostructures2017In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 7, article id 075303Article in journal (Refereed)
    Abstract [en]

    Previously, graphene nanoribbons set in lateral heterostructures with hexagonal boron nitride were predicted to support topologically protected states at low energy. We investigate how robust the transport properties of these states are against lattice disorder. We find that forms of disorder that do not couple the two valleys of the zigzag graphene nanoribbon do not impact the transport properties at low bias, indicating that these lateral heterostructures are very promising candidates for chip-scale conducting interconnects. Forms of disorder that do couple the two valleys, such as vacancies in the graphene ribbon, or substantial inclusions of armchair edges at the graphene-hexagonal boron nitride interface will negatively affect the transport. However, these forms of disorder are not commonly seen in current experiments.

  • 7. Abeysekara, A. U.
    et al.
    Archer, A.
    Benbow, W.
    Bird, R.
    Brose, R.
    Buchovecky, M.
    Buckley, J. H.
    Bugaev, V.
    Chromey, A. J.
    Connolly, M. P.
    Cui, W.
    Daniel, M. K.
    Falcone, A.
    Feng, Q.
    Finley, J. P.
    Fortson, L.
    Furniss, A.
    Hütten, M.
    Hanna, D.
    Hervet, O.
    Holder, J.
    Hughes, G.
    Humensky, T. B.
    Johnson, C. A.
    Kaaret, P.
    Kar, P.
    Kertzman, M.
    Kieda, D.
    Krause, M.
    Krennrich, F.
    Kumar, S.
    Lang, M. J.
    Lin, T. T. Y.
    McArthur, S.
    Moriarty, P.
    Mukherjee, R.
    O'Brien, S.
    Ong, R. A.
    Otte, A. N.
    Park, N.
    Petrashyk, A.
    Pohl, M.
    Pueschel, E.
    Quinn, J.
    Ragan, K.
    Reynolds, P. T.
    Richards, G. T.
    Roache, E.
    Rulten, C.
    Sadeh, I.
    Santander, M.
    Sembroski, G. H.
    Shahinyan, K.
    Sushch, I.
    Tyler, J.
    Wakely, S. P.
    Weinstein, A.
    Wells, R. M.
    Wilcox, P.
    Wilhelm, A.
    Williams, D. A.
    Williamson, T. J.
    Zitzer, B.
    Abdollahi, S.
    Ajello, M.
    Baldini, L.
    Barbiellini, G.
    Bastieri, D.
    Bellazzini, R.
    Berenji, B.
    Bissaldi, E.
    Blandford, R. D.
    Bonino, R.
    Bottacini, E.
    Brandt, T. J.
    Bruel, P.
    Buehler, R.
    Cameron, R. A.
    Caputo, R.
    Caraveo, P. A.
    Castro, D.
    Cavazzuti, E.
    Charles, E.
    Chiaro, G.
    Ciprini, S.
    Cohen-Tanugi, J.
    Costantin, D.
    Cutini, S.
    D'Ammando, F.
    Palma, F. D.
    Lalla, N. D.
    Mauro, M. D.
    Venere, L. D.
    Dominguez, A.
    Favuzzi, C.
    Fegan, S. J.
    Franckowiak, A.
    Fukazawa, Y.
    Funk, S.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Giglietto, N.
    Giordano, F.
    Giroletti, M.
    Green, D.
    Grenier, I. A.
    Guillemot, L.
    Guiriec, S.
    Hays, E.
    Hewitt, J. W.
    Horan, D.
    Jóhannesson, Gudlaugur
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Science Institute, University of Iceland, Reykjavik, IS-107, Iceland.
    Kensei, S.
    Kuss, M.
    Larsson, Stefan
    KTH, School of Engineering Sciences (SCI), Physics. Oskar Klein Centre for Cosmoparticle Physics, AlbaNova, Stockholm, SE-106 91, Sweden.
    Latronico, L.
    Lemoine-Goumard, M.
    Li, J.
    Longo, F.
    Loparco, F.
    Lovellette, M. N.
    Lubrano, P.
    Magill, J. D.
    Maldera, S.
    Mazziotta, M. N.
    McEnery, J. E.
    Michelson, P. F.
    Mitthumsiri, W.
    Mizuno, T.
    Monzani, M. E.
    Morselli, A.
    Moskalenko, I. V.
    Negro, M.
    Nuss, E.
    Ojha, R.
    Omodei, N.
    Orienti, M.
    Orlando, E.
    Palatiello, M.
    Paliya, V. S.
    Paneque, D.
    Perkins, J. S.
    Persic, M.
    Pesce-Rollins, M.
    Petrosian, V.
    Piron, F.
    Porter, T. A.
    Principe, G.
    Raino, S.
    Rando, R.
    Rani, B.
    Razzano, M.
    Razzaque, S.
    Reimer, A.
    Reimer, O.
    Reposeur, T.
    Sgro, C.
    Siskind, E. J.
    Spandre, G.
    Spinelli, P.
    Suson, D. J.
    Tajima, H.
    Thayer, J. B.
    Thompson, D. J.
    Torres, D. F.
    Tosti, G.
    Troja, E.
    Valverde, J.
    Vianello, G.
    Vogel, M.
    Wood, K.
    Yassine, M.
    Alfaro, R.
    Alvarez, C.
    Alvarez, J. D.
    Arceo, R.
    Arteaga-Velázquez, J. C.
    Rojas, D. A.
    Solares, H. A. A.
    Becerril, A.
    Belmont-Moreno, E.
    Benzvi, S. Y.
    Bernal, A.
    Braun, J.
    Brisbois, C.
    Caballero-Mora, K. S.
    Capistrán, T.
    Carraminana, A.
    Casanova, S.
    Castillo, M.
    Cotti, U.
    Cotzomi, J.
    De León, S. C.
    León, C. D.
    Fuente, E. D. L.
    Dichiara, S.
    Dingus, B. L.
    Duvernois, M. A.
    Diaz-Vélez, J. C.
    Engel, K.
    Enriquez-Rivera, O.
    Fiorino, D. W.
    Fleischhack, H.
    Fraija, N.
    Garcia-González, J. A.
    Garfias, F.
    Munoz, A. G.
    González, M. M.
    Goodman, J. A.
    Hampel-Arias, Z.
    Harding, J. P.
    Hernandez, S.
    Hernandez-Almada, A.
    Hona, B.
    Hueyotl-Zahuantitla, F.
    Hui, C. M.
    Hüntemeyer, P.
    Iriarte, A.
    Jardin-Blicq, A.
    Joshi, V.
    Kaufmann, S.
    Lara, A.
    Lauer, R. J.
    Lee, W. H.
    Lennarz, D.
    Vargas, H. L.
    Linnemann, J. T.
    Longinotti, A. L.
    Luis-Raya, G.
    Luna-Garcia, R.
    López-Coto, R.
    Malone, K.
    Marinelli, S. S.
    Martinez, O.
    Martinez-Castellanos, I.
    Martinez-Castro, J.
    Martinez-Huerta, H.
    Matthews, J. A.
    Miranda-Romagnoli, P.
    Moreno, E.
    Mostafá, M.
    Nayerhoda, A.
    Nellen, L.
    Newbold, M.
    Nisa, M. U.
    Noriega-Papaqui, R.
    Pelayo, R.
    Pretz, J.
    Pérez-Pérez, E. G.
    Ren, Z.
    Rho, C. D.
    Riviere, C.
    Rosa-González, D.
    Rosenberg, M.
    Ruiz-Velasco, E.
    Salazar, H.
    Greus, F. S.
    Sandoval, A.
    Schneider, M.
    Arroyo, M. S.
    Sinnis, G.
    Smith, A. J.
    Springer, R. W.
    Surajbali, P.
    Taboada, I.
    Tibolla, O.
    Tollefson, K.
    Torres, I.
    Ukwatta, T. N.
    Villasenor, L.
    Weisgarber, T.
    Westerhoff, S.
    Wisher, I. G.
    Wood, J.
    Yapici, T.
    Yodh, G.
    Zepeda, A.
    Zhou, H.
    VERITAS and Fermi-LAT Observations of TeV Gamma-Ray Sources Discovered by HAWC in the 2HWC Catalog2018In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 866, no 1, article id 24Article in journal (Refereed)
    Abstract [en]

    The High Altitude Water Cherenkov (HAWC) collaboration recently published their 2HWC catalog, listing 39 very high energy (VHE; >100 GeV) gamma-ray sources based on 507 days of observation. Among these, 19 sources are not associated with previously known teraelectronvolt (TeV) gamma-ray sources. We have studied 14 of these sources without known counterparts with VERITAS and Fermi-LAT. VERITAS detected weak gamma-ray emission in the 1 TeV-30 TeV band in the region of DA 495, a pulsar wind nebula coinciding with 2HWC J1953+294, confirming the discovery of the source by HAWC. We did not find any counterpart for the selected 14 new HAWC sources from our analysis of Fermi-LAT data for energies higher than 10 GeV. During the search, we detected gigaelectronvolt (GeV) gamma-ray emission coincident with a known TeV pulsar wind nebula, SNR G54.1+0.3 (VER J1930+188), and a 2HWC source, 2HWC J1930+188. The fluxes for isolated, steady sources in the 2HWC catalog are generally in good agreement with those measured by imaging atmospheric Cherenkov telescopes. However, the VERITAS fluxes for SNR G54.1+0.3, DA 495, and TeV J2032+4130 are lower than those measured by HAWC, and several new HAWC sources are not detected by VERITAS. This is likely due to a change in spectral shape, source extension, or the influence of diffuse emission in the source region.

  • 8.
    Abolmasov, Pavel
    et al.
    Univ Turku, Dept Phys & Astron, Turku 20014, Finland.;Moscow MV Lomonosov State Univ, Sternberg Astron Inst, Univ Sky Pr 13, Moscow 119234, Russia..
    Nättilä, Joonas
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Columbia Univ, Phys Dept, 538 West 120th St, New York, NY 10027 USA.;Columbia Univ, Columbia Astrophys Lab, 538 West 120th St, New York, NY 10027 USA.;Flatiron Inst, Ctr Computat Astrophys, 162 Fifth Ave, New York, NY 10010 USA.;Stockholm Univ, Roslagstullsbacken 23, S-10691 Stockholm, Sweden..
    Poutanen, Juri
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Univ Turku, Dept Phys & Astron, Turku 20014, Finland.;Stockholm Univ, Roslagstullsbacken 23, S-10691 Stockholm, Sweden.;Russian Acad Sci, Space Res Inst, Profsoyuznaya Str 84-32, Moscow 117997, Russia..
    Kilohertz quasi-periodic oscillations from neutron star spreading layers2020In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 638, p. A142-Article in journal (Refereed)
    Abstract [en]

    When the accretion disc around a weakly magnetised neutron star (NS) meets the stellar surface, it should brake down to match the rotation of the NS, forming a boundary layer. As the mechanisms potentially responsible for this braking are apparently inefficient, it is reasonable to consider this layer as a spreading layer (SL) with negligible radial extent and structure. We perform hydrodynamical 2D spectral simulations of an SL, considering the disc as a source of matter and angular momentum. Interaction of new, rapidly rotating matter with the pre-existing, relatively slow material co-rotating with the star leads to instabilities capable of transferring angular momentum and creating variability on dynamical timescales. For small accretion rates, we find that the SL is unstable for heating instability that disrupts the initial latitudinal symmetry and produces large deviations between the two hemispheres. This instability also results in breaking of the axial symmetry as coherent flow structures are formed and escape from the SL intermittently. At enhanced accretion rates, the SL is prone to shearing instability and acts as a source of oblique waves that propagate towards the poles, leading to patterns that again break the axial symmetry. We compute artificial light curves of an SL viewed at different inclination angles. Most of the simulated light curves show oscillations at frequencies close to 1 kHz. We interpret these oscillations as inertial modes excited by shear instabilities near the boundary of the SL. Their frequencies, dependence on flux, and amplitude variations can explain the high-frequency pair quasi-periodic oscillations observed in many low-mass X-ray binaries.

  • 9. Abolmasov, Pavel
    et al.
    Poutanen, Juri
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Gamma-ray opacity of the anisotropic stratified broad-line regions in blazars2017In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 464, no 1, p. 152-169Article in journal (Refereed)
    Abstract [en]

    The GeV-range spectra of blazars are shaped not only by non-thermal emission processes internal to the relativistic jet but also by external pair-production absorption on the thermal emission of the accretion disc and the broad-line region (BLR). For the first time, we compute here the pair-production opacities in the GeV range produced by a realistic BLR accounting for the radial stratification and radiation anisotropy. Using photoionization modelling with the CLOUDY code, we calculate a series of BLR models of different sizes, geometries, cloud densities, column densities and metallicities. The strongest emission features in the model BLR are Ly alpha and He II Ly alpha. Contribution of recombination continua is smaller, especially for hydrogen, because Ly continuum is efficiently trapped inside the large optical depth BLR clouds and converted to Lyman emission lines and higher order recombination continua. The largest effects on the gamma-ray opacity are produced by the BLR geometry and localization of the gamma-ray source. We show that when the gamma-ray source moves further from the central source, all the absorption details move to higher energies and the overall level of absorption drops because of decreasing incidence angles between the gamma-rays and BLR photons. The observed positions of the spectral breaks can be used to measure the geometry and the location of the gamma-ray emitting region relative to the BLR. Strong dependence on geometry means that the soft photons dominating the pair-production opacity may be actually produced by a different population of BLR clouds than the bulk of the observed broad line emission.

  • 10.
    Abolmasov, Pavel
    et al.
    Univ Turku, Dept Phys & Astron, Turku 20014, Finland.;Moscow MV Lomonosov State Univ, Sternberg Astron Inst, Univ Sky Pr 13, Moscow 119234, Russia..
    Poutanen, Juri
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Univ Turku, Dept Phys & Astron, Turku 20014, Finland.;Russian Acad Sci, Space Res Inst, Profsoyuznaya 84-32, Moscow 117997, Russia..
    Mechanical model of a boundary layer for the parallel tracks of kilohertz quasi-periodic oscillations in accreting neutron stars2021In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 647, article id A45Article in journal (Refereed)
    Abstract [en]

    Kilohertz-scale quasi-periodic oscillations (kHz QPOs) are a distinct feature of the variability of neutron star low-mass X-ray binaries. Among all the variability modes, they are especially interesting as a probe for the innermost parts of the accretion flow, including the accretion boundary layer (BL) on the surface of the neutron star. All the existing models of kHz QPOs explain only part of their rich phenomenology. Here, we show that some of their properties can be explained by a very simple model of the BL that is spun up by accreting rapidly rotating matter from the disk and spun down by the interaction with the neutron star. In particular, if the characteristic time scales for the mass and the angular momentum transfer from the BL to the star are of the same order of magnitude, our model naturally reproduces the so-called parallel tracks effect, where the QPO frequency is correlated with luminosity at time scales of hours but becomes uncorrelated at time scales of days. The closeness of the two time scales responsible for mass and angular momentum exchange between the BL and the star is an expected outcome of the radial structure of the BL.

  • 11.
    Ackermann, M.
    et al.
    DESY, D-15738 Zeuthen, Germany..
    Ajello, M.
    Clemson Univ, Kinard Lab Phys, Dept Phys & Astron, Clemson, SC 29634 USA..
    Baldini, L.
    Univ Pisa, Sez Pisa, I-56127 Pisa, Italy.;Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    Ballet, J.
    Univ Paris Diderot, CEA Saclay, Serv Astrophys, CNRS,Lab AIM,CEA IRFU, F-91191 Gif Sur Yvette, France..
    Barbiellini, G.
    Ist Nazl Fis Nucl, Seze Trieste, I-34127 Trieste, Italy.;Univ Trieste, Dipartimento Fis, I-34127 Trieste, Italy..
    Bastieri, D.
    Ist Nazl Fis Nucl, Sez Padova, I-35131 Padua, Italy.;Univ Padua, Dipartimento Fis & Astron G Galilei, I-35131 Padua, Italy..
    Bellazzini, R.
    Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    Bissaldi, E.
    Univ Bari, Dipartimento Fis M Merlin, I-70126 Bari, Italy.;Politecn Bari, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Blandford, R. D.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Bloom, E. D.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Bonino, R.
    Ist Nazl Fis Nucl, Sez Torino, I-10125 Turin, Italy.;Univ Turin, Dipartimento Fis, I-10125 Turin, Italy..
    Bottacini, E.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA.;Univ Padua, Dept Phys & Astron, Vicolo Osservatorio 3, I-35122 Padua, Italy..
    Brandt, T. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Bregeon, J.
    Univ Montpellier, CNRS IN2P3, Lab Univ & Particules Montpellier, F-34095 Montpellier, France..
    Bruel, P.
    Ecole Polytech, IN2P3, CNRS, Lab Leprince Ringuet, F-91128 Palaiseau, France..
    Buehler, R.
    DESY, D-15738 Zeuthen, Germany..
    Cameron, R. A.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Caputo, R.
    CRESST, Greenbelt, MD 20771 USA.;NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Caraveo, P. A.
    INAF Ist Astrofis Spaziale & Fis Cosm Milano, Via E Bassini 15, I-20133 Milan, Italy..
    Castro, D.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.;Harvard Smithsonian Ctr Astrophys, Cambridge, MA 02138 USA..
    Cavazzuti, E.
    Italian Space Agcy, Via Politecn Snc, I-00133 Rome, Italy..
    Charles, E.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Cheung, C. C.
    Naval Res Lab, Div Space Sci, Washington, DC 20375 USA..
    Chiaro, G.
    INAF Ist Astrofis Spaziale & Fis Cosm Milano, Via E Bassini 15, I-20133 Milan, Italy..
    Ciprini, S.
    Space Sci Data Ctr Agenzia Spaziale Italiana, Via Politecn Snc, I-00133 Rome, Italy.;Ist Nazl Fis Nucl, Sez Perugia, I-06123 Perugia, Italy..
    Cohen-Tanugi, J.
    Univ Montpellier, CNRS IN2P3, Lab Univ & Particules Montpellier, F-34095 Montpellier, France..
    Costantin, D.
    Univ Padua, Dipartimento Fis & Astron G Galilei, I-35131 Padua, Italy..
    Cutini, S.
    Space Sci Data Ctr Agenzia Spaziale Italiana, Via Politecn Snc, I-00133 Rome, Italy.;Ist Nazl Fis Nucl, Sez Perugia, I-06123 Perugia, Italy..
    D'Ammando, F.
    INAF Ist Radioastron, I-40129 Bologna, Italy.;Univ Bologna, Dipartimento Astron, I-40127 Bologna, Italy..
    de Palma, F.
    Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy.;Univ Telemat Pegaso, Piazza Trieste & Trento 48, I-80132 Naples, Italy..
    Desai, A.
    Clemson Univ, Kinard Lab Phys, Dept Phys & Astron, Clemson, SC 29634 USA..
    Di Lalla, N.
    Univ Pisa, Sez Pisa, I-56127 Pisa, Italy.;Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    Di Mauro, M.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Di Venere, L.
    Univ Bari, Dipartimento Fis M Merlin, I-70126 Bari, Italy.;Politecn Bari, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Favuzzi, C.
    Univ Bari, Dipartimento Fis M Merlin, I-70126 Bari, Italy.;Politecn Bari, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Finke, J.
    Naval Res Lab, Div Space Sci, Washington, DC 20375 USA..
    Franckowiak, A.
    DESY, D-15738 Zeuthen, Germany..
    Fukazawa, Y.
    Hiroshima Univ, Dept Phys Sci, Hiroshima 7398526, Japan..
    Funk, S.
    Friedrich Alexander Univ Erlangen Nurnberg, Erlangen Ctr Astroparticle Phys, Erwin Rommel Str 1, D-91058 Erlangen, Germany..
    Fusco, P.
    Univ Bari, Dipartimento Fis M Merlin, I-70126 Bari, Italy.;Politecn Bari, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Gargano, F.
    Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Gasparrini, D.
    Space Sci Data Ctr Agenzia Spaziale Italiana, Via Politecn Snc, I-00133 Rome, Italy.;Ist Nazl Fis Nucl, Sez Perugia, I-06123 Perugia, Italy..
    Giglietto, N.
    Univ Bari, Dipartimento Fis M Merlin, I-70126 Bari, Italy.;Politecn Bari, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Giordano, F.
    Univ Bari, Dipartimento Fis M Merlin, I-70126 Bari, Italy.;Politecn Bari, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Giroletti, M.
    INAF Ist Radioastron, I-40129 Bologna, Italy..
    Green, D.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.;Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Grenier, I. A.
    Univ Paris Diderot, CEA Saclay, Serv Astrophys, CNRS,Lab AIM,CEA IRFU, F-91191 Gif Sur Yvette, France..
    Guillemot, L.
    Univ Orleans, CNRS, Lab Phys & Chim Environnem & Espace, F-45071 Orleans 02, France.;CNRS INSU, Observ Paris, Stn Radioastron Nancay, F-18330 Nancay, France..
    Guiriec, S.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.;George Washington Univ, Dept Phys, 725 21st St, Washington, DC 20052 USA..
    Hays, E.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Hewitt, J. W.
    Univ North Florida, Dept Phys, 1 UNF Dr, Jacksonville, FL 32224 USA..
    Horan, D.
    Ecole Polytech, IN2P3, CNRS, Lab Leprince Ringuet, F-91128 Palaiseau, France..
    Jóhannesson, Gudlaugur
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Univ Iceland, Sci Inst, IS-107 Reykjavik, Iceland.
    Kensei, S.
    Hiroshima Univ, Dept Phys Sci, Hiroshima 7398526, Japan..
    Kuss, M.
    Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    Larsson, Stefan
    KTH, School of Engineering Sciences (SCI), Physics.
    Latronico, L.
    Ist Nazl Fis Nucl, Sez Torino, I-10125 Turin, Italy..
    Lemoine-Goumard, M.
    Univ Bordeaux 1, IN2P3 CNRS, Ctr Etudes Nucl Bordeaux Gradignan, BP120, F-33175 Gradignan, France..
    Li, J.
    Inst Space Sci CSICIEEC, Campus UAB,Carrer Magrans S-N, E-08193 Barcelona, Spain..
    Longo, F.
    Ist Nazl Fis Nucl, Seze Trieste, I-34127 Trieste, Italy.;Univ Trieste, Dipartimento Fis, I-34127 Trieste, Italy..
    Loparco, F.
    Univ Bari, Dipartimento Fis M Merlin, I-70126 Bari, Italy.;Politecn Bari, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Lovellette, M. N.
    Naval Res Lab, Div Space Sci, Washington, DC 20375 USA..
    Lubrano, P.
    Ist Nazl Fis Nucl, Sez Perugia, I-06123 Perugia, Italy..
    Magill, J. D.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Maldera, S.
    Ist Nazl Fis Nucl, Sez Torino, I-10125 Turin, Italy..
    Manfreda, A.
    Univ Pisa, Sez Pisa, I-56127 Pisa, Italy.;Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    Mazziotta, M. N.
    Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    McEnery, J. E.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.;Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Meyer, M.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Mizuno, T.
    Hiroshima Univ, Hiroshima Astrophys Sci Ctr, Hiroshima 7398526, Japan..
    Monzani, M. E.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Morselli, A.
    Ist Nazl Fis Nucl, Sez Roma Tor Vergata, I-00133 Rome, Italy..
    Moskalenko, I. V.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Negro, M.
    Ist Nazl Fis Nucl, Sez Torino, I-10125 Turin, Italy.;Univ Turin, Dipartimento Fis, I-10125 Turin, Italy..
    Nuss, E.
    Univ Montpellier, CNRS IN2P3, Lab Univ & Particules Montpellier, F-34095 Montpellier, France..
    Omodei, N.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Orienti, M.
    INAF Ist Radioastron, I-40129 Bologna, Italy..
    Orlando, E.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Ormes, J. F.
    Univ Denver, Dept Phys & Astron, Denver, CO 80208 USA..
    Palatiello, M.
    Ist Nazl Fis Nucl, Seze Trieste, I-34127 Trieste, Italy.;Univ Trieste, Dipartimento Fis, I-34127 Trieste, Italy..
    Paliya, V. S.
    Clemson Univ, Kinard Lab Phys, Dept Phys & Astron, Clemson, SC 29634 USA..
    Paneque, D.
    Max Planck Inst Phys & Astrophys, D-80805 Munich, Germany..
    Perkins, J. S.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Persic, M.
    Ist Nazl Fis Nucl, Seze Trieste, I-34127 Trieste, Italy.;Ist Nazl Astrofis, Osservatorio Astronom Trieste, I-34143 Trieste, Italy..
    Pesce-Rollins, M.
    Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    Piron, F.
    Univ Montpellier, CNRS IN2P3, Lab Univ & Particules Montpellier, F-34095 Montpellier, France..
    Porter, T. A.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Principe, G.
    Friedrich Alexander Univ Erlangen Nurnberg, Erlangen Ctr Astroparticle Phys, Erwin Rommel Str 1, D-91058 Erlangen, Germany..
    Raino, S.
    Univ Bari, Dipartimento Fis M Merlin, I-70126 Bari, Italy.;Politecn Bari, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Rando, R.
    Ist Nazl Fis Nucl, Sez Padova, I-35131 Padua, Italy.;Univ Padua, Dipartimento Fis & Astron G Galilei, I-35131 Padua, Italy..
    Rani, B.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Razzaque, S.
    Univ Johannesburg, Dept Phys, POB 524,Auckland Pk, ZA-2006 Auckland Pk, South Africa..
    Reimer, A.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA.;Leopold Franzens Univ Innsbruck, Inst Astro & Teilchenphys, A-6020 Innsbruck, Austria.;Leopold Franzens Univ Innsbruck, Inst Theoret Phys, A-6020 Innsbruck, Austria..
    Reimer, O.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA.;Leopold Franzens Univ Innsbruck, Inst Astro & Teilchenphys, A-6020 Innsbruck, Austria.;Leopold Franzens Univ Innsbruck, Inst Theoret Phys, A-6020 Innsbruck, Austria..
    Reposeur, T.
    Univ Bordeaux 1, IN2P3 CNRS, Ctr Etudes Nucl Bordeaux Gradignan, BP120, F-33175 Gradignan, France..
    Sgro, C.
    Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    Siskind, E. J.
    NYCB Real Time Comp Inc, Lattingtown, NY 11560 USA..
    Spandre, G.
    Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    Spinelli, P.
    Univ Bari, Dipartimento Fis M Merlin, I-70126 Bari, Italy.;Politecn Bari, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Suson, D. J.
    Purdue Univ Northwest, Hammond, IN 46323 USA..
    Tajima, H.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA.;Nagoya Univ, Solar Terr Environm Lab, Nagoya, Aichi 4648601, Japan..
    Thayer, J. B.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Tibaldo, L.
    CNRS, IRAP, F-310284 Toulouse 4, France.;Univ Toulouse, GAHEC, UPS OMP, IRAP, F-31400 Toulouse, France..
    Torres, D. F.
    Inst Space Sci CSICIEEC, Campus UAB,Carrer Magrans S-N, E-08193 Barcelona, Spain.;ICREA, E-08010 Barcelona, Spain..
    Tosti, G.
    Ist Nazl Fis Nucl, Sez Perugia, I-06123 Perugia, Italy.;Univ Perugia, Dipartimento Fis, I-06123 Perugia, Italy..
    Valverde, J.
    Ecole Polytech, IN2P3, CNRS, Lab Leprince Ringuet, F-91128 Palaiseau, France..
    Venters, T. M.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Vogel, M.
    Calif State Univ Los Angeles, Dept Phys & Astron, Los Angeles, CA 90032 USA..
    Wood, K.
    Praxis Inc, Alexandria, VA 22303 USA.;Naval Res Lab, Washington, DC 20375 USA..
    Wood, M.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Zaharijas, G.
    Ist Nazl Fis Nucl, Sez Trieste, I-34127 Trieste, Italy.;Univ Trieste, I-34127 Trieste, Italy.;Univ Nova Gorica, Ctr Astrophys & Cosmol, Nova Gorica, Slovenia..
    Biteau, J.
    Univ Paris 11, Univ Paris Saclay, Inst Phys Nucl, 15 Rue Georges Clemenceau, F-91406 Orsay, France..
    The Search for Spatial Extension in High-latitude Sources Detected by the Fermi Large Area Telescope2018In: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 237, no 2, p. 32-, article id 32Article in journal (Refereed)
    Abstract [en]

    We present a search for spatial extension in high-latitude (vertical bar b vertical bar > 5 degrees) sources in recent Fermi point source catalogs. The result is the Fermi High-Latitude Extended Sources Catalog, which provides source extensions (or upper limits thereof) and likelihood profiles for a suite of tested source morphologies. We find 24. extended sources, 19 of which were not previously characterized as extended. These include sources that are potentially associated with supernova remnants and star-forming regions. We also found extended.-ray emission in the vicinity of the Cen. A radio lobes and-at GeV energies for the first time-spatially coincident with the radio emission of the SNR CTA 1, as well as from the Crab Nebula. We also searched for halos around active galactic nuclei, which are predicted from electromagnetic cascades induced by the e(+)e(-) pairs that are deflected in intergalactic magnetic fields. These pairs are produced when gamma-rays interact with background radiation fields. We do not find evidence for extension in individual sources or in stacked source samples. This enables us to place limits on the flux of the extended source components, which are then used to constrain the intergalactic magnetic field to be stronger than 3 x 10(-16) G for a coherence length lambda greater than or similar to 10 kpc, even when conservative assumptions on the source duty cycle are made. This improves previous limits by several orders of magnitude.

  • 12.
    Ackermann, M.
    et al.
    Deutsches Elekt Synchrotron DESY, D-15738 Zeuthen, Germany..
    Ajello, M.
    Clemson Univ, Dept Phys & Astron, Kinard Lab Phys, Clemson, SC 29634 USA..
    Baldini, L.
    Univ Pisa, I-56127 Pisa, Italy.;Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    Ballet, J.
    CEA Saclay, Serv Astrophys, Univ Paris Diderot, Lab AIM,CEA IRFU,CNRS, F-91191 Gif Sur Yvette, France..
    Barbiellini, G.
    Ist Nazl Fis Nucl, Sez Trieste, I-34127 Trieste, Italy.;Univ Trieste, Dipartimento Fis, I-34127 Trieste, Italy..
    Bastieri, D.
    Ist Nazl Fis Nucl, Sez Padova, I-35131 Padua, Italy.;Univ Padua, Dipartimento Fis Astron G Galilei, I-35131 Padua, Italy..
    Bellazzini, R.
    Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    Bissaldi, E.
    M Merlin Univ, Dipartimento Fis, I-70126 Bari, Italy.;Politecn Bari, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Blandford, R. D.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Bonino, R.
    Ist Nazl Fis Nucl, Sez Torino, I-10125 Turin, Italy.;Univ Torino, Dipartimento Fis, I-10125 Turin, Italy..
    Bottacini, E.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA.;Univ Padua, Dept Phys & Astron, Vicolo Osservatorio 3, I-35122 Padua, Italy..
    Bregeon, J.
    Univ Montpellier, Lab Univers & Particules Montpellier, CNRS IN2P3, F-34095 Montpellier, France..
    Bruel, P.
    Ecole Polytech, CNRS IN2P3, Lab Leprince Ringuet, F-91128 F- Palaiseau, France..
    Buehler, R.
    Deutsches Elekt Synchrotron DESY, D-15738 Zeuthen, Germany..
    Burns, E.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Buson, S.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Cameron, R. A.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Caputo, R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.;CRESST, Greenbelt, MD 20771 USA..
    Caraveo, P. A.
    INAF, Ist Astrofis Spaziale & Fis Cosm Milano, Via E Bassini 15, I-20133 Milan, Italy..
    Cavazzuti, E.
    Italian Space Agcy, Via Politecn Snc, I-00133 Rome, Italy..
    Chen, S.
    Ist Nazl Fis Nucl, Sez Padova, I-35131 Padua, Italy.;Univ Padua, Dept Phys & Astron, Vicolo Osservatorio 3, I-35122 Padua, Italy..
    Chiaro, G.
    INAF, Ist Astrofis Spaziale & Fis Cosm Milano, Via E Bassini 15, I-20133 Milan, Italy..
    Ciprini, S.
    Space Sci Data Ctr Agenzia Spaziale Italiana, Via Politecn,Snc, I-00133 Rome, Italy.;Ist Nazl Fis Nucl, Sez Perugia, I-06123 Perugia, Italy..
    Costantin, D.
    Univ Padua, Dipartimento Fis Astron G Galilei, I-35131 Padua, Italy..
    Cuoco, A.
    Ist Nazl Fis Nucl, Sez Torino, I-10125 Turin, Italy.;Rhein Westfal TH Aachen, Inst Theoret Particle Phys & Cosmol, TTK, D-52056 Aachen, Germany..
    Cutini, S.
    Space Sci Data Ctr Agenzia Spaziale Italiana, Via Politecn,Snc, I-00133 Rome, Italy.;Ist Nazl Fis Nucl, Sez Perugia, I-06123 Perugia, Italy..
    D'Ammando, F.
    INAF Ist Radioastron, I-40129 Bologna, Italy.;Univ Bologna, Dipartimento Astron, I-40127 Bologna, Italy..
    Luque, P. de la Torre
    M Merlin Univ, Dipartimento Fis, I-70126 Bari, Italy.;Politecn Bari, I-70126 Bari, Italy..
    de Palma, F.
    Ist Nazl Fis Nucl, Sez Torino, I-10125 Turin, Italy..
    Desai, A.
    Clemson Univ, Dept Phys & Astron, Kinard Lab Phys, Clemson, SC 29634 USA..
    Digel, S. W.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Di Lalla, N.
    Univ Pisa, I-56127 Pisa, Italy.;Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    Di Mauro, M.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Di Venere, L.
    M Merlin Univ, Dipartimento Fis, I-70126 Bari, Italy.;Politecn Bari, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Dirirsa, F. Fana
    Univ Johannesburg, Dept Phys, POB 524, ZA-2006 Auckland Pk, South Africa..
    Favuzzi, C.
    M Merlin Univ, Dipartimento Fis, I-70126 Bari, Italy.;Politecn Bari, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Franckowiak, A.
    Deutsches Elekt Synchrotron DESY, D-15738 Zeuthen, Germany..
    Fukazawa, Y.
    Hiroshima Univ, Dept Phys Sci, Higashihiroshima, Hiroshima 7398526, Japan..
    Funk, S.
    Friedrich Alexander Univ Erlangen Nurnberg, Erlangen Ctr Astroparticle Phys, Erwin Rommel Str 1, D-91058 Erlangen, Germany..
    Fusco, P.
    M Merlin Univ, Dipartimento Fis, I-70126 Bari, Italy.;Politecn Bari, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Gargano, F.
    Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Gasparrini, D.
    Space Sci Data Ctr Agenzia Spaziale Italiana, Via Politecn,Snc, I-00133 Rome, Italy.;Ist Nazl Fis Nucl, Sez Perugia, I-06123 Perugia, Italy..
    Giglietto, N.
    M Merlin Univ, Dipartimento Fis, I-70126 Bari, Italy.;Politecn Bari, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Giordano, F.
    M Merlin Univ, Dipartimento Fis, I-70126 Bari, Italy.;Politecn Bari, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Giroletti, M.
    INAF Ist Radioastron, I-40129 Bologna, Italy..
    Green, D.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.;Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Grenier, I. A.
    CEA Saclay, Serv Astrophys, Univ Paris Diderot, Lab AIM,CEA IRFU,CNRS, F-91191 Gif Sur Yvette, France..
    Guillemot, L.
    Univ Orleans, Lab Phys & Chim Environm & Espace, CNRS, F-45071 Orleans, France.;CNRS, INSU, Observ Paris, Stat Radioastron Nancay, F-18330 Nancay, France..
    Guiriec, S.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.;George Washington Univ, Dept Phys, 725 21st St,NW, Washington, DC 20052 USA..
    Horan, D.
    Ecole Polytech, CNRS IN2P3, Lab Leprince Ringuet, F-91128 F- Palaiseau, France..
    Jóhannesson, Gudlaugur
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Univ Iceland, Sci Inst, IS-107 Reykjavik, Iceland.Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden..
    Kuss, M.
    Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    Larsson, S.
    AlbaNova, Oskar Klein Ctr Cosmoparticle Phys, SE-10691 Stockholm, Sweden..
    Latronico, L.
    Ist Nazl Fis Nucl, Sez Torino, I-10125 Turin, Italy..
    Li, J.
    Deutsches Elekt Synchrotron DESY, D-15738 Zeuthen, Germany..
    Liodakis, I.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Longo, F.
    Ist Nazl Fis Nucl, Sez Trieste, I-34127 Trieste, Italy.;Univ Trieste, Dipartimento Fis, I-34127 Trieste, Italy..
    Loparco, F.
    M Merlin Univ, Dipartimento Fis, I-70126 Bari, Italy.;Politecn Bari, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Lubrano, P.
    Ist Nazl Fis Nucl, Sez Perugia, I-06123 Perugia, Italy..
    Magill, J. D.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Maldera, S.
    Ist Nazl Fis Nucl, Sez Torino, I-10125 Turin, Italy..
    Malyshev, D.
    Friedrich Alexander Univ Erlangen Nurnberg, Erlangen Ctr Astroparticle Phys, Erwin Rommel Str 1, D-91058 Erlangen, Germany..
    Manfreda, A.
    Univ Pisa, I-56127 Pisa, Italy.;Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    Mazziotta, M. N.
    Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Mereu, I.
    Univ Perugia, Dipartimento Fis, I-06123 Perugia, Italy..
    Michelson, P. F.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Mitthumsiri, W.
    Mahidol Univ, Dept Phys, Fac Sci, Bangkok 10400, Thailand..
    Mizuno, T.
    Hiroshima Univ, Hiroshima Astrophys Sci Ctr, Higashihiroshima, Hiroshima 7398526, Japan..
    Monzani, M. E.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Morselli, A.
    Ist Nazl Fis Nucl, Sez Roma Tor Vergata, I-00133 Rome, Italy..
    Moskalenko, I. V.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Negro, M.
    Ist Nazl Fis Nucl, Sez Torino, I-10125 Turin, Italy.;Univ Torino, Dipartimento Fis, I-10125 Turin, Italy..
    Nuss, E.
    Univ Montpellier, Lab Univers & Particules Montpellier, CNRS IN2P3, F-34095 Montpellier, France..
    Orienti, M.
    INAF Ist Radioastron, I-40129 Bologna, Italy..
    Orlando, E.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Palatiello, M.
    Ist Nazl Fis Nucl, Sez Trieste, I-34127 Trieste, Italy.;Univ Trieste, Dipartimento Fis, I-34127 Trieste, Italy..
    Paliya, V. S.
    Clemson Univ, Dept Phys & Astron, Kinard Lab Phys, Clemson, SC 29634 USA..
    Paneque, D.
    Max Planck Inst Phys & Astrophys, D-80805 Munich, Germany..
    Persic, M.
    Ist Nazl Fis Nucl, Sez Trieste, I-34127 Trieste, Italy.;Ist Nazl Astrofis, Osservatorio Astronom Trieste, I-34143 Trieste, Italy..
    Pesce-Rollins, M.
    Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    Petrosian, V.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Piron, F.
    Univ Montpellier, Lab Univers & Particules Montpellier, CNRS IN2P3, F-34095 Montpellier, France..
    Porter, T. A.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Principe, G.
    Friedrich Alexander Univ Erlangen Nurnberg, Erlangen Ctr Astroparticle Phys, Erwin Rommel Str 1, D-91058 Erlangen, Germany..
    Raino, S.
    M Merlin Univ, Dipartimento Fis, I-70126 Bari, Italy.;Politecn Bari, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Rando, R.
    Ist Nazl Fis Nucl, Sez Padova, I-35131 Padua, Italy.;Univ Padua, Dipartimento Fis Astron G Galilei, I-35131 Padua, Italy..
    Razzano, M.
    Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    Razzaque, S.
    Univ Johannesburg, Dept Phys, POB 524, ZA-2006 Auckland Pk, South Africa..
    Reimer, A.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA.;Leopold Franzens Univ Innsbruck, Inst Astro & Teilchenphys, A-6020 Innsbruck, Austria.;Leopold Franzens Univ Innsbruck, Inst Theoret Phys, A-6020 Innsbruck, Austria..
    Reimer, O.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA.;Leopold Franzens Univ Innsbruck, Inst Astro & Teilchenphys, A-6020 Innsbruck, Austria.;Leopold Franzens Univ Innsbruck, Inst Theoret Phys, A-6020 Innsbruck, Austria..
    Serini, D.
    M Merlin Univ, Dipartimento Fis, I-70126 Bari, Italy.;Politecn Bari, I-70126 Bari, Italy..
    Sgro, C.
    Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    Siskind, E. J.
    NYCB Real Time Comp Inc, Lattingtown, NY 11560 USA..
    Spandre, G.
    Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    Spinelli, P.
    M Merlin Univ, Dipartimento Fis, I-70126 Bari, Italy.;Politecn Bari, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Suson, D. J.
    Purdue Univ Northwest, Hammond, IN 46323 USA..
    Tajima, H.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA.;Nagoya Univ, Solar Terr Environm Lab, Nagoya, Aichi 4648601, Japan..
    Takahashi, M.
    Max Planck Inst Phys & Astrophys, D-80805 Munich, Germany..
    Thayer, J. B.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Tibaldo, L.
    Univ Toulouse, IRAP, CNRS, UPS,CNES, F-31028 Toulouse, France..
    Torres, D. F.
    Inst Space Sci CSICIEEC, Campus UAB,Carrer Magrans S-N, E-08193 Barcelona, Spain.;ICREA, E-08010 Barcelona, Spain..
    Troja, E.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.;Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Venters, T. M.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Vianello, G.
    Stanford Univ, WW Hansen Expt Phys Lab, Kavli Inst Particle Astrophys & Cosmol, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Wood, K.
    Praxis Inc, Alexandria, VA 22303 USA.;Naval Res Lab, Washington, DC 20375 USA..
    Yassine, M.
    Ist Nazl Fis Nucl, Sez Trieste, I-34127 Trieste, Italy.;Univ Trieste, Dipartimento Fis, I-34127 Trieste, Italy..
    Zaharijas, G.
    Univ Trieste, Ist Nazl Fis Nucl, Sez Trieste, I-34127 Trieste, Italy.;Univ Trieste, I-34127 Trieste, Italy.;Univ Nova Gorica, Ctr Astrophys & Cosmol, Nova Gorica 5000, Slovenia..
    Ammazzalorso, S.
    Ist Nazl Fis Nucl, Sez Torino, I-10125 Turin, Italy.;Univ Torino, Dipartimento Fis, I-10125 Turin, Italy..
    Fornengo, N.
    Ist Nazl Fis Nucl, Sez Torino, I-10125 Turin, Italy.;Univ Torino, Dipartimento Fis, I-10125 Turin, Italy..
    Regis, M.
    Ist Nazl Fis Nucl, Sez Torino, I-10125 Turin, Italy.;Univ Torino, Dipartimento Fis, I-10125 Turin, Italy..
    Unresolved Gamma-Ray Sky through its Angular Power Spectrum2018In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 121, no 24, article id 241101Article in journal (Refereed)
    Abstract [en]

    The gamma-ray sky has been observed with unprecedented accuracy in the last decade by the Fermi-large area telescope (LAT), allowing us to resolve and understand the high-energy Universe. The nature of the remaining unresolved emission [unresolved gamma-ray background (UGRB)] below the LAT source detection threshold can be uncovered by characterizing the amplitude and angular scale of the UGRB fluctuation field. This Letter presents a measurement of the UGRB autocorrelation angular power spectrum based on eight years of Fermi-LAT Pass 8 data products. The analysis is designed to be robust against contamination from resolved sources and noise systematics. The sensitivity to subthreshold sources is greatly enhanced with respect to previous measurements. We find evidence (with similar to 3.7 sigma significance) that the scenario in which two classes of sources contribute to the UGRB signal is favored over a single class. A double power law with exponential cutoff can explain the anisotropy energy spectrum well, with photon indices of the two populations being 2.55 +/- 0.23 and 1.86 +/- 0.15.

  • 13.
    Ackley, K.
    et al.
    Monash Univ, Sch Phys & Astron, Clayton, Vic 3800, Australia..
    Bulla, Mattia
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Roslagstullsbacken 23, S-10691 Stockholm, Sweden..
    Levan, A. J.
    Univ Warwick, Dept Phys, Coventry CV4 7AL, W Midlands, England.;Radboud Univ Nijmegen, Dept Astrophys, IMAPP, POB 9010, NL-6500 GL Nijmegen, Netherlands..
    Young, D. R.
    Queens Univ Belfast, Astrophys Res Ctr, Sch Math & Phys, Belfast BT7 1NN, Antrim, North Ireland..
    et al.,
    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.

  • 14.
    Addazi, A.
    et al.
    Sichuan Univ, Coll Phys, Ctr Theoret Phys, Chengdu 610065, Peoples R China.;Ist Nazl Fis Nucl, Lab Nazl Frascati, Via Enrico Fermi 54, I-00044 Rome, Italy..
    Carmona, J. M.
    Univ Zaragoza, Ctr Astroparticulas & Fis Altas Energias CAPA, Dept Fis Teor, C Pedro Cerbuna 12, E-50009 Zaragoza, Spain..
    Obers, Niels A.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Hannes Alfvens Vag 12, SE-10691 Stockholm, Sweden.;Univ Copenhagen, Niels Bohr Inst, DK-2100 Copenhagen, Denmark..
    Zornoza, J. D.
    Univ Valencia, CSIC, Inst Fis Corpuscular, Parc Cient UV,C Catedrat Jose Beltran 2, E-46980 Paterna, Spain..
    Quantum gravity phenomenology at the dawn of the multi-messenger era-A review2022In: Progress in Particle and Nuclear Physics, ISSN 0146-6410, E-ISSN 1873-2224, Vol. 125, article id 103948Article, review/survey (Refereed)
    Abstract [en]

    The exploration of the universe has recently entered a new era thanks to the multi-messenger paradigm, characterized by a continuous increase in the quantity and quality of experimental data that is obtained by the detection of the various cosmic messengers (photons, neutrinos, cosmic rays and gravitational waves) from numerous origins. They give us information about their sources in the universe and the properties of the intergalactic medium. Moreover, multi-messenger astronomy opens up the possibility to search for phenomenological signatures of quantum gravity. On the one hand, the most energetic events allow us to test our physical theories at energy regimes which are not directly accessible in accelerators; on the other hand, tiny effects in the propagation of very high energy particles could be amplified by cosmological distances. After decades of merely theoretical investigations, the possibility of obtaining phenomenological indications of Planck-scale effects is a revolutionary step in the quest for a quantum theory of gravity, but it requires cooperation between different communities of physicists (both theoretical and experimental). This review, prepared within the COST Action CA18108 "Quantum gravity phenomenology in the multi-messenger approach", is aimed at promoting this cooperation by giving a state-of-the art account of the interdisciplinary expertise that is needed in the effective search of quantum gravity footprints in the production, propagation and detection of cosmic messengers.

  • 15.
    Afonso, Marco Martins
    et al.
    Univ Porto, Fac Ciencias, Ctr Matemat, Rua Campo Alegre 687, P-4169007 Porto, Portugal..
    Mitra, Dhrubaditya
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Vincenzi, Dario
    Univ Cote dAzur, CNRS, LJAD, F-06100 Nice, France..
    Kazantsev dynamo in turbulent compressible flows2019In: Proceedings of the Royal Society. Mathematical, Physical and Engineering Sciences, ISSN 1364-5021, E-ISSN 1471-2946, Vol. 475, no 2223, article id 20180591Article in journal (Refereed)
    Abstract [en]

    We consider the kinematic fluctuation dynamo problem in a flow that is random, white-in-time, with both solenoidal and potential components. This model is a generalization of the well-studied Kazantsev model. If both the solenoidal and potential parts have the same scaling exponent, then, as the compressibility of the flow increases, the growth rate decreases but remains positive. If the scaling exponents for the solenoidal and potential parts differ, in particular if they correspond to typical Kolmogorov and Burgers values, we again find that an increase in compressibility slows down the growth rate but does not turn it off. The slow down is, however, weaker and the critical magnetic Reynolds number is lower than when both the solenoidal and potential components display the Kolmogorov scaling. Intriguingly, we find that there exist cases, when the potential part is smoother than the solenoidal part, for which an increase in compressibility increases the growth rate. We also find that the critical value of the scaling exponent above which a dynamo is seen is unity irrespective of the compressibility. Finally, we realize that the dimension d = 3 is special, as for all other values of d the critical exponent is higher and depends on the compressibility.

  • 16. Agarwal, Abhishek
    et al.
    Lipstein, Arthur E.
    Young, Donovan
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Scattering amplitudes of massive N = 2 gauge theories in three dimensions2014In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 89, no 4, p. 045020-Article in journal (Refereed)
    Abstract [en]

    We study the scattering amplitudes of mass-deformed Chern-Simons theories and Yang-Mills-Chern-Simons theories with N = 2 supersymmetry in three dimensions. In particular, we derive the on-shell supersymmetry algebras which underlie the scattering matrices of these theories. We then compute various 3 and 4-point on-shell tree-level amplitudes in these theories. For the mass-deformed Chern-Simons theory, odd-point amplitudes vanish and we find that all of the 4-point amplitudes can be encoded elegantly in superamplitudes. For the Yang-Mills-Chern-Simons theory, we obtain all of the 4-point tree-level amplitudes using a combination of perturbative techniques and algebraic constraints and we comment on difficulties related to computing amplitudes with external gauge fields using Feynman diagrams. Finally, we propose a Britto-Cachazo-Feng-Witten recursion relation for mass-deformed theories in three dimensions and discuss the applicability of this proposal to mass-deformed N = 2 theories.

  • 17. Agarwal, S.
    et al.
    Wettlaufer, J. S.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Yale University, New Haven, CT, USA; Mathematical Institute, University of Oxford, Oxford, UK.
    Fluctuations in Arctic sea-ice extent: Comparing observations and climate models2018In: Philosophical Transactions. Series A: Mathematical, physical, and engineering science, ISSN 1364-503X, E-ISSN 1471-2962, Vol. 376, no 2129, article id 20170332Article in journal (Refereed)
    Abstract [en]

    The fluctuation statistics of the observed sea-ice extent during the satellite era are compared with model output from CMIP5 models using a multifractal time series method. The two robust features of the observations are that on annual to biannual time scales the ice extent exhibits white noise structure, and there is a decadal scale trend associated with the decay of the ice cover. It is shown that (i) there is a large inter-model variability in the time scales extracted from the models, (ii) none of the models exhibits the decadal time scales found in the satellite observations, (iii) five of the 21 models examined exhibit the observed white noise structure, and (iv) the multi-model ensemble mean exhibits neither the observed white noise structure nor the observed decadal trend. It is proposed that the observed fluctuation statistics produced by this method serve as an appropriate test bed for modelling studies. 

  • 18. Agarwal, Sahil
    et al.
    Del Sordo, Fabio
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Wettlaufer, John S.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    EXOPLANETARY DETECTION BY MULTIFRACTAL SPECTRAL ANALYSIS2017In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 153, no 1, article id 12Article in journal (Refereed)
    Abstract [en]

    Owing to technological advances, the number of exoplanets discovered has risen dramatically in the last few years. However, when trying to observe Earth analogs, it is often difficult to test the veracity of detection. We have developed a new approach to the analysis of exoplanetary spectral observations based on temporal multifractality, which identifies timescales that characterize planetary orbital motion around the host star and those that arise from stellar features such as spots. Without fitting stellar models to spectral data, we show how the planetary signal can be robustly detected from noisy data using noise amplitude as a source of information. For observation of transiting planets, combining this method with simple geometry allows us to relate the timescales obtained to primary and secondary eclipse of the exoplanets. Making use of data obtained with ground-based and space-based observations we have tested our approach on HD 189733b. Moreover, we have investigated the use of this technique in measuring planetary orbital motion via Doppler shift detection. Finally, we have analyzed synthetic spectra obtained using the SOAP 2.0 tool, which simulates a stellar spectrum and the influence of the presence of a planet or a spot on that spectrum over one orbital period. We have demonstrated that, so long as the signal-to-noise-ratio >= 75, our approach reconstructs the planetary orbital period, as well as the rotation period of a spot on the stellar surface.

  • 19.
    Agarwal, Sahil
    et al.
    Yale Univ, Program Appl Math, New Haven, CT 06520 USA..
    Wettlaufer, John
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Yale Univ, Program Appl Math, New Haven, CT 06520 USA.;Royal Inst Technol, Nordita, SE-10691 Stockholm, Sweden.;Stockholm Univ, SE-10691 Stockholm, Sweden..
    Minimal Data Fidelity for Stellar Feature and Companion Detection2022In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 163, no 1, p. 6-, article id 6Article in journal (Refereed)
    Abstract [en]

    Technological advances in instrumentation have led to an exponential increase in exoplanet detection and scrutiny of stellar features such as spots and faculae. While the spots and faculae enable us to understand the stellar dynamics, exoplanets provide us with a glimpse into stellar evolution. While the ubiquity of noise (e.g., telluric, instrumental, or photonic) is unavoidable, combining this with increased spectrographic resolution compounds technological challenges. To account for these noise sources and resolution issues, we use a temporal multifractal framework to study data from the Spot Oscillation And Planet 2.0 tool, which simulates a stellar spectrum in the presence of a spot, a facula or a planet. Given these controlled simulations, we vary the resolution as well as the signal-to-noise ratio (S/N) to obtain a lower limit on the resolution and S/N required to robustly detect features. We show that a spot and a facula with a 1% coverage of the stellar disk can be robustly detected for a S/N (per pixel) of 35 and 60, respectively, for any spectral resolution above 20,000, while a planet with a radial velocity of 10 m s(-1) can be detected for a S/N (per pixel) of 600. Rather than viewing noise as an impediment, our approach uses noise as a source of information.

  • 20. Agarwal, Sahil
    et al.
    Wettlaufer, John S.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Maximal stochastic transport in the Lorenz equations2016In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 380, no 1-2, p. 142-146Article in journal (Refereed)
    Abstract [en]

    We calculate the stochastic upper bounds for the Lorenz equations using an extension of the background method. In analogy with Rayleigh-Benard convection the upper bounds are for heat transport versus Rayleigh number. As might be expected, the stochastic upper bounds are larger than the deterministic counterpart of Souza and Doering [1], but their variation with noise amplitude exhibits interesting behavior. Below the transition to chaotic dynamics the upper bounds increase monotonically with noise amplitude. However, in the chaotic regime this monotonicity depends on the number of realizations in the ensemble; at a particular Rayleigh number the bound may increase or decrease with noise amplitude. The origin of this behavior is the coupling between the noise and unstable periodic orbits, the degree of which depends on the degree to which the ensemble represents the ergodic set. This is confirmed by examining the close returns plots of the full solutions to the stochastic equations and the numerical convergence of the noise correlations. The numerical convergence of both the ensemble and time averages of the noise correlations is sufficiently slow that it is the limiting aspect of the realization of these bounds. Finally, we note that the full solutions of the stochastic equations demonstrate that the effect of noise is equivalent to the effect of chaos.

  • 21. Agarwal, Sahil
    et al.
    Wettlaufer, John S.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Yale University, United States; University of Oxford, United Kingdom.
    The Statistical Properties of Sea Ice Velocity Fields2017In: Journal of Climate, ISSN 0894-8755, E-ISSN 1520-0442, Vol. 30, no 13, p. 4873-4881Article in journal (Refereed)
    Abstract [en]

    By arguing that the surface pressure field over the Arctic Ocean can be treated as an isotropic, stationary, homogeneous, Gaussian random field, Thorndike estimated a number of covariance functions from two years of data (1979 and 1980). Given the active interest in changes of general circulation quantities and indices in the polar regions during the recent few decades, the spatial correlations in sea ice velocity fields are of particular interest. It is thus natural to ask, "How persistent are these correlations?'' To this end, a multifractal stochastic treatment is developed to analyze observed Arctic sea ice velocity fields from satellites and buoys for the period 1978-2015. Since it was previously found that the Arctic equivalent ice extent (EIE) has a white noise structure on annual to biannual time scales, the connection between EIE and ice motion is assessed. The long-term stationarity of the spatial correlation structure of the velocity fields and the robustness of their white noise structure on multiple time scales is demonstrated; these factors (i) combine to explain the white noise characteristics of the EIE on annual to biannual time scales and (ii) explain why the fluctuations in the ice velocity are proportional to fluctuations in the geostrophic winds on time scales of days to months. Moreover, it is shown that the statistical structure of these two quantities is commensurate from days to years, which may be related to the increasing prevalence of free drift in the ice pack.

  • 22.
    Agarwala, Adhip
    et al.
    Tata Inst Fundamental Res, Int Ctr Theoret Sci, Bengaluru 560089, India.;Max Planck Inst Phys Komplexer Syst, Nothnitzer Str 38, D-01187 Dresden, Germany..
    Juricic, Vladimir
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Roslagstullsbacken 23, S-10691 Stockholm, Sweden..
    Roy, Bitan
    Max Planck Inst Phys Komplexer Syst, Nothnitzer Str 38, D-01187 Dresden, Germany.;Lehigh Univ, Dept Phys, Bethlehem, PA 18015 USA..
    Higher-order topological insulators in amorphous solids2020In: Physical Review Research, E-ISSN 2643-1564, Vol. 2, no 1, article id 012067Article in journal (Refereed)
    Abstract [en]

    We identify the possibility of realizing higher order topological (HOT) phases in noncrystalline or amorphous materials. Starting from two- and three-dimensional crystalline HOT insulators, accommodating topological corner states, we gradually enhance structural randomness in the system. Within a parameter regime, as long as amorphousness is confined by an outer crystalline boundary, the system continues to host corner states, yielding amorphous HOT insulators. However, as structural disorder percolates to the edges, corner states start to dissolve into amorphous bulk, and ultimately the system becomes a trivial insulator when amorphousness plagues the entire system. These outcomes are further substantiated by computing the quadrupolar (octupolar) moment in two (three) dimensions. Therefore, HOT phases can be realized in amorphous solids, when wrapped by a thin (lithographically grown, for example) crystalline layer. Our findings suggest that crystalline topological phases can be realized even in the absence of local crystalline symmetry.

  • 23.
    Agasthya, Lokahith
    et al.
    Indian Inst Sci Educ & Res, Pune 411008, Maharashtra, India.;Tata Inst Fundamental Res, Int Ctr Theoret Sci, Bangalore 560089, Karnataka, India.;Univ Roma Tor Vergata, Dept Phys, Via Ric Sci 1, I-00133 Rome, Italy.;Univ Roma Tor Vergata, Ist Nazl Fis Nucl, Via Ric Sci 1, I-00133 Rome, Italy..
    Picardo, Jason R.
    Tata Inst Fundamental Res, Int Ctr Theoret Sci, Bangalore 560089, Karnataka, India..
    Ravichandran, Siddharth
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, S-10691 Stockholm, Sweden..
    Govindarajan, Rama
    Tata Inst Fundamental Res, Int Ctr Theoret Sci, Bangalore 560089, Karnataka, India..
    Ray, Samriddhi Sankar
    Tata Inst Fundamental Res, Int Ctr Theoret Sci, Bangalore 560089, Karnataka, India..
    Understanding droplet collisions through a model flow: Insights from a Burgers vortex2019In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 99, no 6, article id 063107Article in journal (Refereed)
    Abstract [en]

    We investigate the role of intense vortical structures, similar to those in a turbulent flow, in enhancing collisions (and coalescences) which lead to the formation of large aggregates in particle-laden flows. By using a Burgers vortex model, we show, in particular, that vortex stretching significantly enhances sharp inhomogeneities in spatial particle densities, related to the rapid ejection of particles from intense vortices. Furthermore our work shows how such spatial clustering leads to an enhancement of collision rates and extreme statistics of collisional velocities. We also study the role of polydisperse suspensions in this enhancement. Our work uncovers an important principle, which, if valid for realistic turbulent flows, may be a factor in how small nuclei water droplets in warm clouds can aggregate to sizes large enough to trigger rain.

  • 24.
    Agrawal, Vipin
    et al.
    Nordita SU; Stockholm Univ, Roslagstullsbacken 23, S-10691 Stockholm, Sweden.;Stockholm Univ, Dept Phys, S-10691 Stockholm, Sweden..
    Mitra, Dhrubaditya
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Chaos and irreversibility of a flexible filament in periodically driven Stokes flow2022In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 106, no 2, article id 025103Article in journal (Refereed)
    Abstract [en]

    The flow of Newtonian fluid at low Reynolds number is, in general, regular and time-reversible due to absence of nonlinear effects. For example, if the fluid is sheared by its boundary motion that is subsequently reversed, then all the fluid elements return to their initial positions. Consequently, mixing in microchannels happens solely due to molecular diffusion and is very slow. Here, we show, numerically, that the introduction of a single, freely floating, flexible filament in a time-periodic linear shear flow can break reversibility and give rise to chaos due to elastic nonlinearities, if the bending rigidity of the filament is within a carefully chosen range. Within this range, not only the shape of the filament is spatiotemporally chaotic, but also the flow is an efficient mixer. Overall, we find five dynamical phases: the shape of a stiff filament is time-invariant-either straight or buckled; it undergoes a period-two bifurcation as the filament is made softer; becomes spatiotemporally chaotic for even softer filaments but, surprisingly, the chaos is suppressed if bending rigidity is decreased further.

  • 25.
    Agrawal, Vipin
    et al.
    Nordita SU; Department of Physics, Stockholm University, AlbaNova University Centre, Fysikum, 106 91 Stockholm, Sweden, Fysikum.
    Pandey, Vikash
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Mitra, Dhrubaditya
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Active buckling of pressurized spherical shells: Monte Carlo simulation2023In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 108, no 3, article id L032601Article in journal (Refereed)
    Abstract [en]

    We study the buckling of pressurized spherical shells by Monte Carlo simulations in which the detailed balance is explicitly broken - thereby driving the shell to be active, out of thermal equilibrium. Such a shell typically has either higher (active) or lower (sedate) fluctuations compared to one in thermal equilibrium depending on how the detailed balance is broken. We show that, for the same set of elastic parameters, a shell that is not buckled in thermal equilibrium can be buckled if turned active. Similarly a shell that is buckled in thermal equilibrium can unbuckle if sedated. Based on this result, we suggest that it is possible to experimentally design microscopic elastic shells whose buckling can be optically controlled.

  • 26. Ahmed, T.
    et al.
    Albers, R. C.
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Friedrich, C.
    Zhu, J. -X
    G W quasiparticle calculations with spin-orbit coupling for the light actinides2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 3, p. 035104-Article in journal (Refereed)
    Abstract [en]

    We report on the importance of GW self-energy corrections for the electronic structure of light actinides in the weak-to-intermediate coupling regime. Our study is based on calculations of the band structure and total density of states of Np, U, and Pu using a one-shot GW approximation that includes spin-orbit coupling within a full potential LAPW framework. We also present RPA screened effective Coulomb interactions for the f-electron orbitals for different lattice constants, and show that there is an increased contribution from electron-electron correlation in these systems for expanded lattices. We find a significant amount of electronic correlation in these highly localized electronic systems.

  • 27. Ahmed, Towfiq
    et al.
    Haraldsen, Jason T.
    Rehr, John J.
    Di Ventra, Massimiliano
    Schuller, Ivan
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Correlation dynamics and enhanced signals for the identification of serial biomolecules and DNA bases2014In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 25, no 12, p. 125705-Article in journal (Refereed)
    Abstract [en]

    Nanopore-based sequencing has demonstrated a significant potential for the development of fast, accurate, and cost-efficient fingerprinting techniques for next generation molecular detection and sequencing. We propose a specific multilayered graphene-based nanopore device architecture for the recognition of single biomolecules. Molecular detection and analysis can be accomplished through the detection of transverse currents as the molecule or DNA base translocates through the nanopore. To increase the overall signal-to-noise ratio and the accuracy, we implement a new 'multi-point cross-correlation' technique for identification of DNA bases or other molecules on the single molecular level. We demonstrate that the cross-correlations between each nanopore will greatly enhance the transverse current signal for each molecule. We implement first-principles transport calculations for DNA bases surveyed across a multilayered graphene nanopore system to illustrate the advantages of the proposed geometry. A time-series analysis of the cross-correlation functions illustrates the potential of this method for enhancing the signal-to-noise ratio. This work constitutes a significant step forward in facilitating fingerprinting of single biomolecules using solid state technology.

  • 28. Ahmed, Towfiq
    et al.
    Haraldsen, Jason T.
    Zhu, Jian-Xin
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Institute for Materials Science, Los Alamos National Laboratory, United States.
    Next-Generation Epigenetic Detection Technique: Identifying Methylated Cytosine Using Graphene Nanopore2014In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 5, no 15, p. 2601-2607Article in journal (Refereed)
    Abstract [en]

    DNA methylation plays a pivotal role in the genetic evolution of both embryonic and adult cells. For adult somatic cells, the location and dynamics of methylation have been very precisely pinned down with the 5-cytosine markers on cytosine-phosphate-guanine (CpG) units. Unusual methylation on CpG islands is identified as one of the prime causes for silencing the tumor suppressant genes. Early detection of methylation changes can diagnose the potentially harmful oncogenic evolution of cells and provide promising guideline for cancer prevention. With this motivation, we propose a cytosine methylation detection technique. Our hypothesis is that electronic signatures of DNA acquired as a molecule translocates through a nanopore would be significantly different for methylated and nonmethylated bases. This difference in electronic fingerprints would allow for reliable real-time differentiation of methylated DNA. We calculate transport currents through a punctured graphene membrane while the cytosine and methylated cytosine translocate through the nanopore. We also calculate the transport properties for uracil and cyanocytosine for comparison. Our calculations of transmission, current, and tunneling conductance show distinct signatures in their spectrum for each molecular type. Thus, in this work, we provide a theoretical analysis that points to a viability of our hypothesis.

  • 29.
    Ahnen, M. L.
    et al.
    Swiss Fed Inst Technol, CH-8093 Zurich, Switzerland..
    Jóhannesson, Gudlaugur
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Larsson, Stefan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Yassine, M.
    Ist Nazl Fis Nucl, Sez Trieste, I-34127 Trieste, Italy.;Univ Trieste, Dipartimento Fis, I-34127 Trieste, Italy..
    et al.,
    MAGIC and Fermi-LAT gamma-ray results on unassociated HAWC sources2019In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 485, no 1, p. 356-366Article in journal (Refereed)
    Abstract [en]

    The HAWC Collaboration released the 2HWC catalogue of TeV sources, in which 19 show no association with any known high-energy (HE; E greater than or similar to 10 GeV) or very-high-energy (VHE; E greater than or similar to 300 GeV) sources. This catalogue motivated follow-up studies by both the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) and Fermi-LAT (Large Area Telescope) observatories with the aim of investigating gamma-ray emission over a broad energy band. In this paper, we report the results from the first joint work between High Altitude Water Cherenkov (HAWC), MAGIC, and Fermi-LAT on three unassociated HAWC sources: 2HWC J2006+341, 2HWC J1907+084*, and 2HWC J1852+013*. Although no significant detection was found in the HE and VHE regimes, this investigation shows that a minimum 1 degrees extension (at 95 per cent confidence level) and harder spectrum in the GeV than the one extrapolated from HAWC results are required in the case of 2HWC J1852+013*, whilst a simply minimum extension of 0.16 degrees (at 95 per cent confidence level) can already explain the scenario proposed by HAWC for the remaining sources. Moreover, the hypothesis that these sources are pulsar wind nebulae is also investigated in detail.

  • 30. Ahumada, T.
    et al.
    Singer, L. P.
    Anand, S.
    Coughlin, M. W.
    Kasliwal, M. M.
    Ryan, G.
    Andreoni, I.
    Cenko, S. B.
    Fremling, C.
    Kumar, H.
    Pang, P. T. H.
    Burns, E.
    Cunningham, V.
    Dichiara, S.
    Dietrich, T.
    Svinkin, D. S.
    Almualla, M.
    Castro-Tirado, A. J.
    De, K.
    Dunwoody, R.
    Gatkine, P.
    Hammerstein, E.
    Iyyani, S.
    Mangan, J.
    Perley, D.
    Purkayastha, S.
    Bellm, E.
    Bhalerao, V.
    Bolin, B.
    Bulla, Mattia
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Cannella, C.
    Chandra, P.
    Duev, D. A.
    Frederiks, D.
    Gal-Yam, A.
    Graham, M.
    Ho, A. Y. Q.
    Hurley, K.
    Karambelkar, V.
    Kool, E. C.
    Kulkarni, S. R.
    Mahabal, A.
    Masci, F.
    McBreen, S.
    Pandey, S. B.
    Reusch, S.
    Ridnaia, A.
    Rosnet, P.
    Rusholme, B.
    Carracedo, A. S.
    Smith, R.
    Soumagnac, M.
    Stein, R.
    Troja, E.
    Tsvetkova, A.
    Walters, R.
    Valeev, A. F.
    Discovery and confirmation of the shortest gamma-ray burst from a collapsar2021In: Nature Astronomy, E-ISSN 2397-3366, Vol. 5, no 9, p. 917-927Article in journal (Refereed)
    Abstract [en]

    Gamma-ray bursts (GRBs) are among the brightest and most energetic events in the Universe. The duration and hardness distribution of GRBs has two clusters1, now understood to reflect (at least) two different progenitors2. Short-hard GRBs (SGRBs; T90 < 2 s) arise from compact binary mergers, and long-soft GRBs (LGRBs; T90 > 2 s) have been attributed to the collapse of peculiar massive stars (collapsars)3. The discovery of SN 1998bw/GRB 980425 (ref. 4) marked the first association of an LGRB with a collapsar, and AT 2017gfo (ref. 5)/GRB 170817A/GW170817 (ref. 6) marked the first association of an SGRB with a binary neutron star merger, which also produced a gravitational wave. Here, we present the discovery of ZTF20abwysqy (AT2020scz), a fast-fading optical transient in the Fermi satellite and the Interplanetary Network localization regions of GRB 200826A; X-ray and radio emission further confirm that this is the afterglow. Follow-up imaging (at rest-frame 16.5 days) reveals excess emission above the afterglow that cannot be explained as an underlying kilonova, but which is consistent with being the supernova. Although the GRB duration is short (rest-frame T90 of 0.65 s), our panchromatic follow-up data confirm a collapsar origin. GRB 200826A is the shortest LGRB found with an associated collapsar; it appears to sit on the brink between a successful and a failed collapsar. Our discovery is consistent with the hypothesis that most collapsars fail to produce ultra-relativistic jets.

  • 31.
    Ajello, M.
    et al.
    Clemson Univ, Dept Phys & Astron, Kinard Lab Phys, Clemson, SC 29634 USA..
    Arimoto, M.
    Kanazawa Univ, Inst Sci & Engn, Fac Math & Phys, Kanazawa, Ishikawa 9201192, Japan..
    Axelsson, Magnus
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Jóhannesson, Gudlaugur
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Larsson, Stefan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    De Pasquale, M.
    Fermi and Swift Observations of GRB 190114C: Tracing the Evolution of High-energy Emission from Prompt to Afterglow2020In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 890, no 1, article id 9Article in journal (Refereed)
    Abstract [en]

    We report on the observations of gamma-ray burst (GRB) 190114C by the Fermi Gamma -ray Space Telescope and the Neil Gehrels Swift Observatory. The prompt gamma-ray emission was detected by the Fermi GRB Monitor (GBM), the Fermi Large Area Telescope (LAT), and the Swift Burst Alert Telescope (BAT) and the long-lived afterglow emission was subsequently observed by the GBM, LAT, Swift X-ray Telescope (XRT), and Swift UV Optical Telescope. The early -time observations reveal multiple emission components that evolve independently, with a delayed power-law component that exhibits significant spectral attenuation above 40 MeV in the first few seconds of the burst. This power-law component transitions to a harder spectrum that is consistent with the afterglow emission observed by the XRT at later times. This afterglow component is clearly identifiable in the GBM and BAT light curves as a slowly fading emission component on which the rest of the prompt emission is superimposed. As a result, we are able to observe the transition from internal-shock- to external-shock-dominated emission. We find that the temporal and spectral evolution of the broadband afterglow emission can be well modeled as synchrotron emission from a forward shock propagating into a wind -like circumstellar environment. We estimate the initial bulk Lorentz factor using the observed high-energy spectral cutoff. Considering the onset of the afterglow component, we constrain the deceleration radius at which this forward shock begins to radiate in order to estimate the maximum synchrotron energy as a function of time. We find that even in the LAT energy range, there exist high-energy photons that are in tension with the theoretical maximum energy that can be achieved through synchrotron emission from a shock. These violations of the maximum synchrotron energy are further compounded by the detection of very high-energy (VHE) emission above 300 GeV by MAGIC concurrent with our observations. We conclude that the observations of VHE photons from GRB 190114C necessitates either an additional emission mechanism at very high energies that is hidden in the synchrotron component in the LAT energy range, an acceleration mechanism that imparts energy to the particles at a rate that is faster than the electron synchrotron energy -loss rate, or revisions of the fundamental assumptions used in estimating the maximum photon energy attainable through the synchrotron process.

  • 32. Ajello, M.
    et al.
    Atwood, W. B.
    Axelsson, Magnus
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Baldini, L.
    Barbiellini, G.
    Baring, M. G.
    Bastieri, D.
    Bellazzini, R.
    Berretta, A.
    Bissaldi, E.
    Blandford, R. D.
    Bonino, R.
    Bregeon, J.
    Bruel, P.
    Buehler, R.
    Burns, E.
    Buson, S.
    Cameron, R. A.
    Caraveo, P. A.
    Cavazzuti, E.
    Chen, S.
    Cheung, C. C.
    Chiaro, G.
    Ciprini, S.
    Costantin, D.
    Crnogorcevic, M.
    Cutini, S.
    D’Ammando, F.
    de la Torre Luque, P.
    de Palma, F.
    Digel, S. W.
    Di Lalla, N.
    Di Venere, L.
    Dirirsa, F. F.
    Fukazawa, Y.
    Funk, S.
    Fusco, P.
    Gargano, F.
    Giglietto, N.
    Gill, R.
    Giordano, F.
    Giroletti, M.
    Granot, J.
    Green, D.
    Grenier, I. A.
    Griffin, S.
    Guiriec, S.
    Hays, E.
    Horan, D.
    Jóhannesson, Gudlaugur
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Kerr, M.
    Kovačević, M.
    Kuss, M.
    Larsson, Stefan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Latronico, L.
    Li, J.
    Longo, F.
    Loparco, F.
    Lovellette, M. N.
    Lubrano, P.
    Maldera, S.
    Manfreda, A.
    Martí-Devesa, G.
    Mazziotta, M. N.
    McEnery, J. E.
    Mereu, I.
    Michelson, P. F.
    Mizuno, T.
    Monzani, M. E.
    Morselli, A.
    Moskalenko, I. V.
    Negro, M.
    Omodei, N.
    Orienti, M.
    Orlando, E.
    Paliya, V. S.
    Paneque, D.
    Pei, Z.
    Pesce-Rollins, M.
    Piron, F.
    Poon, H.
    Porter, T. A.
    Principe, G.
    Racusin, J. L.
    Rainò, S.
    Rando, R.
    Rani, B.
    Razzaque, S.
    Reimer, A.
    Reimer, O.
    Parkinson, P. M. S.
    Scargle, J. D.
    Scotton, L.
    Serini, D.
    Sgrò, C.
    Siskind, E. J.
    Spandre, G.
    Spinelli, P.
    Tajima, H.
    Takahashi, M. N.
    Tak, D.
    Torres, D. F.
    Tosti, G.
    Troja, E.
    Wadiasingh, Z.
    Wood, K.
    Yassine, M.
    Yusafzai, A.
    Zaharijas, G.
    High-energy emission from a magnetar giant flare in the Sculptor galaxy2021In: Nature Astronomy, E-ISSN 2397-3366, Vol. 5, no 4, p. 385-391Article in journal (Refereed)
    Abstract [en]

    Magnetars are the most highly magnetized neutron stars in the cosmos (with magnetic field 1013–1015 G). Giant flares from magnetars are rare, short-duration (about 0.1 s) bursts of hard X-rays and soft γ rays1,2. Owing to the limited sensitivity and energy coverage of previous telescopes, no magnetar giant flare has been detected at gigaelectronvolt (GeV) energies. Here, we report the discovery of GeV emission from a magnetar giant flare on 15 April 2020 (refs. 3,4 and A. J. Castro-Tirado et al., manuscript in preparation). The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope detected GeV γ rays from 19 s until 284 s after the initial detection of a signal in the megaelectronvolt (MeV) band. Our analysis shows that these γ rays are spatially associated with the nearby (3.5 megaparsecs) Sculptor galaxy and are unlikely to originate from a cosmological γ-ray burst. Thus, we infer that the γ rays originated with the magnetar giant flare in Sculptor. We suggest that the GeV signal is generated by an ultra-relativistic outflow that first radiates the prompt MeV-band photons, and then deposits its energy far from the stellar magnetosphere. After a propagation delay, the outflow interacts with environmental gas and produces shock waves that accelerate electrons to very high energies; these electrons then emit GeV γ rays as optically thin synchrotron radiation. This observation implies that a relativistic outflow is associated with the magnetar giant flare, and suggests the possibility that magnetars can power some short γ-ray bursts.

  • 33. Ajello, M.
    et al.
    Atwood, W. B.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Bastieri, D.
    Bellazzini, R.
    Bissaldi, E.
    Blandford, R. D.
    Bloom, E. D.
    Bonino, R.
    Bregeon, J.
    Britto, R. J.
    Bruel, P.
    Buehler, R.
    Buson, S.
    Cameron, R. A.
    Caputo, R.
    Caragiulo, M.
    Caraveo, P. A.
    Cavazzuti, E.
    Cecchi, C.
    Charles, E.
    Chekhtman, A.
    Cheung, C. C.
    Chiaro, G.
    Ciprini, S.
    Cohen, J. M.
    Costantin, D.
    Costanza, F.
    Cuoco, A.
    Cutini, S.
    D'Ammando, F.
    de Palma, F.
    Desiante, R.
    Digel, S. W.
    Di Lalla, N.
    Di Mauro, M.
    Di Venere, L.
    Dominguez, A.
    Drell, P. S.
    Dumora, D.
    Favuzzi, C.
    Fegan, S. J.
    Ferrara, E. C.
    Fortin, P.
    Franckowiak, A.
    Fukazawa, Y.
    Funk, S.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Giglietto, N.
    Giommi, P.
    Giordano, F.
    Giroletti, M.
    Glanzman, T.
    Green, D.
    Grenier, I. A.
    Grondin, M. -H
    Grove, J. E.
    Guillemot, L.
    Guiriec, S.
    Harding, A. K.
    Hays, E.
    Hewitt, J. W.
    Horan, D.
    Jóhannesson, Gudlaugur
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Kensei, S.
    Kuss, M.
    La Mura, G.
    Larsson, Stefan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Latronico, L.
    Lemoine-Goumard, M.
    Li, J.
    Longo, F.
    Loparco, F.
    Lott, B.
    Lubrano, P.
    Magill, J. D.
    Maldera, S.
    Manfreda, A.
    Mazziotta, M. N.
    McEnery, J. E.
    Meyer, M.
    Michelson, P. F.
    Mirabal, N.
    Mitthumsiri, W.
    Mizuno, T.
    Moiseev, A. A.
    Monzani, M. E.
    Morselli, A.
    Moskalenko, I. V.
    Negro, M.
    Nuss, E.
    Ohsugi, T.
    Omodei, N.
    Orienti, M.
    Orlando, E.
    Palatiello, M.
    Paliya, V. S.
    Paneque, D.
    Perkins, J. S.
    Persic, M.
    Pesce-Rollins, M.
    Piron, F.
    Porter, T. A.
    Principe, G.
    Raino, S.
    Rando, R.
    Razzano, M.
    Razzaque, S.
    Reimer, A.
    Reimer, O.
    Reposeur, T.
    Parkinson, P. M. Saz
    Sgro, C.
    Simone, D.
    Siskind, E. J.
    Spada, F.
    Spandre, G.
    Spinelli, P.
    Stawarz, L.
    Suson, D. J.
    Takahashi, M.
    Tak, D.
    Thayer, J. G.
    Thayer, J. B.
    Thompson, D. J.
    Torres, D. F.
    Torresi, E.
    Troja, E.
    Vianello, G.
    Wood, K.
    Wood, M.
    3FHL: The Third Catalog of Hard Fermi-LAT Sources2017In: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 232, no 2, article id 18Article in journal (Refereed)
  • 34.
    Ajello, M.
    et al.
    Clemson Univ, Dept Phys & Astron, Kinard Lab Phys, Clemson, SC 29634 USA..
    Axelsson, Magnus
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Stockholm Univ, Dept Phys, AlbaNova, SE-10691 Stockholm, Sweden.
    Cameron, R. A.
    Stanford Univ, Dept Phys, Kavli Inst Particle Astrophys & Cosmol, WW Hansen Expt Phys Lab, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Jóhannesson, Gudlaugur
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Univ Iceland, Sci Inst, IS-107 Reykjavik, Iceland. Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden..
    Larsson, Stefan
    KTH, School of Engineering Sciences (SCI), Physics. Dalarna Univ, Sch Educ Hlth & Social Studies, Nat Sci, SE-79188 Falun, Sweden..
    Zaharijas, G.
    Ist Nazl Fis Nucl, Sez Trieste, I-34127 Trieste, Italy.;Univ Nova Gorica, Ctr Astrophys & Cosmol, Nova Gorica, Slovenia..
    Fermi Large Area Telescope Performance after 10 Years of Operation2021In: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 256, no 1, article id 12Article in journal (Refereed)
    Abstract [en]

    The Large Area Telescope (LAT), the primary instrument for the Fermi Gamma-ray Space Telescope (Fermi) mission, is an imaging, wide field-of-view, high-energy gamma-ray telescope, covering the energy range from 30 MeV to more than 300 GeV. We describe the performance of the instrument at the 10 yr milestone. LAT performance remains well within the specifications defined during the planning phase, validating the design choices and supporting the compelling case to extend the duration of the Fermi mission. The details provided here will be useful when designing the next generation of high-energy gamma-ray observatories.

  • 35.
    Ajello, M.
    et al.
    Clemson Univ, Dept Phys & Astron, Kinard Lab Phys, Clemson, SC 29634 USA..
    Axelsson, Magnus
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ciprini, S.
    Jóhannesson, Gudlaugur
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Larsson, Stefan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Yassine, M.
    The Fourth Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope2020In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 892, no 2, article id 105Article in journal (Refereed)
    Abstract [en]

    The fourth catalog of active galactic nuclei (AGNs) detected by the Fermi Gamma-ray Space Telescope Large Area Telescope (4LAC) between 2008 August 4 and 2016 August 2 contains . It includes 85% more sources than the previous 3LAC catalog based on 4 yr of data. AGNs represent at least 79% of the high-latitude sources in the fourth Fermi-Large Area Telescope Source Catalog (4FGL), which covers the energy range from 50 MeV to 1 TeV. In addition, gamma-ray AGNs are found at low Galactic latitudes. Most of the 4LAC AGNs are blazars (98%), while the remainder are other types of AGNs. The blazar population consists of 24% Flat Spectrum Radio Quasars (FSRQs), 38% BL Lac-type objects, and 38% blazar candidates of unknown types (BCUs). On average, FSRQs display softer spectra and stronger variability in the gamma-ray band than BL Lacs do, confirming previous findings. All AGNs detected by ground-based atmospheric Cerenkov telescopes are also found in the 4LAC.

  • 36.
    Ajello, M.
    et al.
    Clemson Univ, Dept Phys & Astron, Kinard Lab Phys, Clemson, SC 29634 USA..
    Johannesson, Gudlaugur
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Univ Iceland, Sci Inst, IS-107 Reykjavik, Iceland.;Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden..
    Larsson, Stefan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. AlbaNova, Oskar Klein Ctr Cosmoparticle Phys, SE-10691 Stockholm, Sweden.;Dalarna Univ, Sch Educ Hlth & Social Studies, Nat Sci, SE-79188 Falun, Sweden..
    Zrake, J.
    Clemson Univ, Dept Phys & Astron, Kinard Lab Phys, Clemson, SC 29634 USA..
    Gamma Rays from Fast Black-hole Winds2021In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 921, no 2, article id 144Article in journal (Refereed)
    Abstract [en]

    Massive black holes at the centers of galaxies can launch powerful wide-angle winds that, if sustained over time, can unbind the gas from the stellar bulges of galaxies. These winds may be responsible for the observed scaling relation between the masses of the central black holes and the velocity dispersion of stars in galactic bulges. Propagating through the galaxy, the wind should interact with the interstellar medium creating a strong shock, similar to those observed in supernovae explosions, which is able to accelerate charged particles to high energies. In this work we use data from the Fermi Large Area Telescope to search for the gamma-ray emission from galaxies with an ultrafast outflow (UFO): a fast (v similar to 0.1 c), highly ionized outflow, detected in absorption at hard X-rays in several nearby active galactic nuclei (AGN). Adopting a sensitive stacking analysis we are able to detect the average gamma-ray emission from these galaxies and exclude that it is due to processes other than UFOs. Moreover, our analysis shows that the gamma-ray luminosity scales with the AGN bolometric luminosity and that these outflows transfer similar to 0.04% of their mechanical power to gamma-rays. Interpreting the observed gamma-ray emission as produced by cosmic rays (CRs) accelerated at the shock front, we find that the gamma-ray emission may attest to the onset of the wind-host interaction and that these outflows can energize charged particles up to the transition region between galactic and extragalactic CRs.

  • 37.
    Ajello, M.
    et al.
    Clemson Univ, Dept Phys & Astron, Kinard Lab Phys, Clemson, SC 29634 USA..
    Jóhannesson, Gudlaugur
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Univ Iceland, Sci Inst, IS-107 Reykjavik, Iceland.;NORDITA, Royal Inst Technol, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden.;Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden..
    Kerr, M.
    Naval Res Lab, Space Sci Div, Washington, DC 20375 USA..
    Larsson, Stefan
    KTH, School of Engineering Sciences (SCI), Applied Physics. Oskar Klein Ctr Cosmoparticle Phys, AlbaNova, SE-10691 Stockholm, Sweden.;Dalarna Univ, Sch Educ Hlth & Social Studies, Nat Sci, SE-79188 Falun, Sweden..
    Parthasarathy, A.
    Max Planck Inst Radioastron, Hugel 69, D-53121 Bonn, Germany..
    Zaharijas, G.
    Univ Nova Gorica, Ctr Astrophys & Cosmol, Nova Gorica, Slovenia..
    A gamma-ray pulsar timing array constrains the nanohertz gravitational wave background2022In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 376, no 6592, p. 521-523Article in journal (Refereed)
    Abstract [en]

    After large galaxies merge, their central supermassive black holes are expected to form binary systems. Their orbital motion should generate a gravitational wave background (GWB) at nanohertz frequencies. Searches for this background use pulsar timing arrays, which perform long-term monitoring of millisecond pulsars at radio wavelengths. We used 12.5 years of Fermi Large Area Telescope data to form a gamma-ray pulsar timing array. Results from 35 bright gamma-ray pulsars place a 95% credible limit on the GWB characteristic strain of 1.0 x 10(-14) at a frequency of 1 year(-1). The sensitivity is expected to scale with t(obs), the observing time span, as t(obs)(-13/6). This direct measurement provides an independent probe of the GWB while offering a check on radio noise models.

  • 38.
    Ajello, M.
    et al.
    Clemson Univ, Dept Phys & Astron, Kinard Lab Phys, Clemson, SC 29634 USA..
    Jóhannesson, Gudlaugur
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Univ Iceland, Sci Inst, IS-107 Reykjavik, Iceland. ; Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden..
    Zimmer, S.
    Leopold Franzens Univ Innsbruck, Inst Astro & Teilchenphys, A-6020 Innsbruck, Austria.;Leopold Franzens Univ Innsbruck, Inst Theoret Phys, A-6020 Innsbruck, Austria.;Univ Geneva, DPNC, 24 Quai Ernest Ansermet, CH-1211 Geneva 4, Switzerland..
    et al.,
    A Search for Cosmic-Ray Proton Anisotropy with the Fermi Large Area Telescope2019In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 883, no 1, article id 33Article in journal (Refereed)
    Abstract [en]

    The Fermi Large Area Telescope (LAT) has amassed a large data set of primary cosmic-ray protons throughout its mission. In fact, it is the largest set of identified cosmic-ray protons ever collected at this energy. The LAT' s wide field of view and full-sky survey capabilities make it an excellent instrument for studying cosmic-ray anisotropy. As a space-based survey instrument, the LAT is sensitive to anisotropy in both R.A. and decl., while ground-based observations only measure the anisotropy in R.A. We present the results of the first-ever proton anisotropy search using Fermi LAT. The data set was collected over eight years and consists of approximately 179 million protons above 78 GeV, enabling it to probe dipole anisotropy below an amplitude of 10(-3), resulting in the most stringent limits on the decl. dependence of the dipole to date. We measure a dipole amplitude delta = 3.9 +/- 1.5 x 10(-4) with a p-value of 0.01 (pretrials) for protons with energy greater than 78 GeV. We discuss various systematic effects that could give rise to a dipole excess and calculate upper limits on the dipole amplitude as a function of minimum energy. The 95% confidence level upper limit on the dipole amplitude is delta(UL) = 1.3 x 10(-3) for protons with energy greater than 78 GeV and delta(UL )= 1.2 x 10(-3) for protons with energy greater than 251 GeV.

  • 39.
    Ajello, Marco
    et al.
    Department of Physics and Astronomy, Clemson University, Kinard Lab of Physics, Clemson, SC 29634-0978, USA.
    Johannesson, Gudni
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Science Institute, University of Iceland, IS-107 Reykjavik, Iceland;Stockholm University, Roslagstullsbacken 23, SE-106 91 Stockholm, Sweden.
    Larsson, Stefan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova, SE-106 91 Stockholm, Sweden; School of Education, Health and Social Studies, Natural Science, Dalarna University, SE-791 88 Falun, Sweden.
    Zrake, J.
    Department of Physics and Astronomy, Clemson University, Kinard Lab of Physics, Clemson, SC 29634-0978, USA.
    Gamma rays from Fast Black-Hole Winds2022In: 37th International Cosmic Ray Conference, ICRC 2021, Sissa Medialab Srl , 2022, article id 596Conference paper (Refereed)
    Abstract [en]

    Massive black holes at the centers of galaxies can launch powerful wide-angle winds that, if sustained over time, can unbind the gas from the stellar bulges of galaxies. These winds may be responsible for the observed scaling relation between the masses of the central black holes and the velocity dispersion of stars in galactic bulges. Propagating through the galaxy, the wind should interact with the interstellar medium creating a strong shock, similar to those observed in supernovae explosions, which is able to accelerate charged particles to high energies. In this work we use data from the Fermi Large Area Telescope to search for the γ-ray emission from galaxies with an ultra-fast outflow (UFO): a fast (v ∼ 0.1c), highly ionized outflow, detected in absorption at hard X-rays in several nearby active galactic nuclei (AGN). Adopting a sensitive stacking analysis we are able to detect the average γ-ray emission from these galaxies and exclude that it is due to processes other than the UFOs. Moreover, our analysis shows that the γ-ray luminosity scales with the AGN bolometric luminosity and that these outflows transfer ∼0.04 % of their mechanical power to γ rays. Interpreting the observed γ-ray emission as produced by cosmic rays (CRs) accelerated at the shock front, we find that the γ-ray emission may attest to the onset of the wind-host interaction and that these outflows can energize charged particles up to the transition region between galactic and extragalactic CRs. A preprint of the full analysis is available on the arXiv: 2105.11469.

  • 40.
    Akrami, Yashar
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Hassan, Sayed Fawad
    Nordita SU;Department of Physics and the Oskar Klein Centre, Stockholm University, AlbaNova University Center, SE 106 91 Stockholm, Sweden.
    Könnig, Frank
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Schmidt-May, Angnis
    Nordita SU;Institut für Theoretische Physik, Eidgenössische Technische Hochschule Zürich, Wolfgang-Pauli-Strasse 27, 8093 Zürich, Switzerland.
    Solomon, Adam R.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Bimetric gravity is cosmologically viable2015In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 748, p. 37-44Article in journal (Refereed)
    Abstract [en]

    Bimetric theory describes gravitational interactions in the presence of an extra spin-2 field. Previous work has suggested that its cosmological solutions are generically plagued by instabilities. We show that by taking the Planck mass for the second metric, M-f, to be small, these instabilities can be pushed back to unobservably early times. In this limit, the theory approaches general relativity with an effective cosmological constant which is, remarkably, determined by the spin-2 interaction scale. This provides a late-time expansion history which is extremely close to Lambda CDM, but with a technically-natural value for the cosmological constant. We find M-f should be no larger than the electroweak scale in order for cosmological perturbations to be stable by big-bang nucleosynthesis. We further show that in this limit the helicity-0 mode is no longer strongly-coupled at low energy scales.

  • 41. Akrami, Yashar
    et al.
    Koivisto, Tomi S.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Solomon, Adam R.
    The nature of spacetime in bigravity: Two metrics or none?2015In: General Relativity and Gravitation, ISSN 0001-7701, E-ISSN 1572-9532, Vol. 47, no 1, p. 1838-Article in journal (Refereed)
    Abstract [en]

    The possibility of matter coupling to two metrics at once is considered. This appears natural in the most general ghost-free, bimetric theory of gravity, where it unlocks an additional symmetry with respect to the exchange of the metrics. This double coupling, however, raises the problem of identifying the observables of the theory. It is shown that if the two metrics couple minimally to matter, then there is no physical metric to which all matter would universally couple, and that moreover such an effective metric generically does not exist even for an individual matter species. By studying point particle dynamics, a resolution is suggested in the context of Finsler geometry.

  • 42.
    Akrami, Yashar
    et al.
    Leiden Univ, Lorentz Inst Theoret Phys, POB 9506, NL-2300 RA Leiden, Netherlands..
    Kuhnel, Florian
    Stockholm Univ, AlbaNova, Oskar Klein Ctr Cosmoparticle Phys, Dept Phys, SE-10691 Stockholm, Sweden..
    Sandstad, Marit
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Uncertainties in primordial black-hole constraints on the primordial power spectrum2018In: Physics of the Dark Universe, E-ISSN 2212-6864, Vol. 19, p. 124-128Article in journal (Refereed)
    Abstract [en]

    The existence (and abundance) of primordial black holes (PBHs) is governed by the power spectrum of primordial perturbations generated during inflation. So far no PBHs have been observed, and instead, increasingly stringent bounds on their existence at different scales have been obtained. Up until recently, this has been exploited in attempts to constrain parts of the inflationary power spectrum that are unconstrained by cosmological observations. We first point out that the simple translation of the PBH non-observation bounds into constraints on the primordial power spectrum is inaccurate as it fails to include realistic aspects of PBH formation and evolution. We then demonstrate, by studying two examples of uncertainties from the effects of critical and non-spherical collapse, that even though they may seem small, they have important implications for the usefulness of the constraints. In particular, we point out that the uncertainty induced by non-spherical collapse may be much larger than the difference between particular bounds from PBH non-observations and the general maximum cap stemming from the condition Omega <= 1 on the dark-matter density in the form of PBHs. We therefore make the cautious suggestion of applying only the overall maximum dark-matter constraint to models of early Universe, as this requirement seems to currently provide a more reliable constraint, which better reflects our current lack of detailed knowledge of PBH formation. These, and other effects, such as merging, clustering and accretion, may also loosen constraints from non-observations of other primordial compact objects such as ultra-compact minihalos of dark matter. 

  • 43.
    Alabarta, K.
    et al.
    Univ Southampton, Sch Phys & Astron, Southampton SO17 1BJ, Hants, England.;Univ Groningen, Kapteyn Astron Inst, POB 800, NL-9700 AV Groningen, Netherlands..
    Altamirano, D.
    Univ Southampton, Sch Phys & Astron, Southampton SO17 1BJ, Hants, England..
    Mendez, M.
    Univ Groningen, Kapteyn Astron Inst, POB 800, NL-9700 AV Groningen, Netherlands..
    Cuneo, V. A.
    Inst Astrofis Canarias IAC, Via Lactea S-N, E-38205 San Cristobal la Laguna, SC De Tenerife, Spain.;Univ La Laguna, Dept Astrofis, E-38205 San Cristobal la Laguna, SC De Tenerife, Spain..
    Vincentelli, F. M.
    Univ Southampton, Sch Phys & Astron, Southampton SO17 1BJ, Hants, England..
    Castro-Segura, N.
    Univ Southampton, Sch Phys & Astron, Southampton SO17 1BJ, Hants, England..
    Garcia, F.
    Univ Groningen, Kapteyn Astron Inst, POB 800, NL-9700 AV Groningen, Netherlands..
    Luff, B.
    Univ Southampton, Sch Phys & Astron, Southampton SO17 1BJ, Hants, England..
    Veledina, Alexandra
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Univ Turku, Dept Phys & Astron, FI-20014 Turku, Finland; Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden.;Russian Acad Sci, Space Res Inst, Profsoyuznaya Str 84-32, Moscow 117997, Russia..
    Failed-transition outbursts in black hole low-mass X-ray binaries2021In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 507, no 4, p. 5507-5522Article in journal (Refereed)
    Abstract [en]

    Black hole low-mass X-ray binaries (BH LMXBs) evolve in a similar way during outburst. Based on the X-ray spectrum and variability, this evolution can be divided into three canonical states: low/hard, intermediate, and high/soft state. BH LMXBs evolve from the low/hard to the high/soft state through the intermediate state in some outbursts (here called 'full outbursts'). However, in other cases, BH LMXBs undergo outbursts in which the source never reaches the high/soft state, here called 'failed-transition outbursts' (FT outbursts). From a sample of 56 BH LMXBs undergoing 128 outbursts, we find that 36 percent of these BH LMXBs experienced at least one FT outburst, and that FT outbursts represent similar to 33 percent of the outbursts of the sample, showing that these are common events. We compare all the available X-ray data of full and FT outbursts of BH LMXBs from RXTE/PCA, Swift/BAT, and MAXI, and find that FT and full outbursts cannot be distinguished from their X-ray light curves, hardness-intensity diagrams, or X-ray variability during the initial 10-60 d after the outburst onset. This suggests that both types of outbursts are driven by the same physical process. We also compare the optical and infrared (O/IR) data of FT and full outbursts of GX 339-4. We found that this system is generally brighter in O/IR bands before an FT outburst, suggesting that the O/IR flux points to the physical process that later leads to a full or an FT outburst. We discuss our results in the context of models that describe the onset and evolution of outbursts in accreting X-ray binaries.

  • 44. Albornoz, N. L. Gonzalez
    et al.
    Schmidt-May, Angnis
    von Strauss, Mikael
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Dark matter scenarios with multiple spin-2 fields2018In: Journal of Cosmology and Astroparticle Physics, E-ISSN 1475-7516, no 1, article id 014Article in journal (Refereed)
    Abstract [en]

    We study ghost-free multimetric theories for (N + 1) tensor fields with a coupling to matter and maximal global symmetry group S-N x (Z(2))(N). Their mass spectra contain a massless mode, the graviton, and N massive spin-2 modes. One of the massive modes is distinct by being the heaviest, the remaining (N - 1) massive modes are simply identical copies of each other. All relevant physics can therefore be understood from the case N = 2. Focussing on this case, we compute the full perturbative action up to cubic order and derive several features that hold to all orders in perturbation theory. The lighter massive mode does not couple to matter and neither of the massive modes decay into massless gravitons. We propose the lighter massive particle as a candidate for dark matter and investigate its phenomenology in the parameter region where the matter coupling is dominated by the massless graviton. The relic density of massive spin-2 can originate from a freeze-in mechanism or from gravitational particle production, giving rise to two different dark matter scenarios. The allowed parameter regions are very different from those in scenarios with only one massive spin-2 field and more accessible to experiments.

  • 45.
    Alessio, Francesco
    et al.
    Nordita SU.
    Di Vecchia, Paolo
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Radiation reaction for spinning black-hole scattering2022In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 832, article id 137258Article in journal (Refereed)
    Abstract [en]

    Starting from the leading soft term of the 5-point amplitude, involving a graviton and two Kerr black holes, that factorises into the product of the elastic amplitude without the graviton and the leading soft factor, we compute the infrared divergent contribution to the imaginary part of the two-loop eikonal. Then, using analyticity and crossing symmetry, we determine the radiative contribution to the real part of the two-loop eikonal and from it the radiative part of the deflection angle for spins aligned to the orbital angular momentum, the loss of angular momentum and the zero frequency limit of the energy spectrum for any spin and for any spin orientation. For spin one we find perfect agreement with recent results obtained with the supersymmetric worldline formalism.

  • 46.
    Almualla, Mouza
    et al.
    Amer Univ Sharjah, Dept Phys, POB 26666, Sharjah, U Arab Emirates..
    Anand, Shreya
    CALTECH, Div Phys Math & Astron, Pasadena, CA 91125 USA..
    Coughlin, Michael W.
    Univ Minnesota, Sch Phys & Astron, Minneapolis, MN 55455 USA..
    Dietrich, Tim
    Univ Potsdam, Inst Phys & Astron, Karl Liebknecht Str 24-25, D-14476 Potsdam, Germany..
    Guessoum, Nidhal
    Amer Univ Sharjah, Dept Phys, POB 26666, Sharjah, U Arab Emirates..
    Carracedo, Ana Sagues
    Stockholm Univ, Oskar Klein Ctr, Dept Phys, AlbaNova, SE-10691 Stockholm, Sweden..
    Ahumada, Tomas
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Andreoni, Igor
    CALTECH, Div Phys Math & Astron, Pasadena, CA 91125 USA..
    Antier, Sarah
    Univ Paris, Astroparticule & Cosmol, CNRS, F-75013 Paris, France..
    Bellm, Eric C.
    Univ Washington, DIRAC Inst, Dept Astron, 3910 15th Ave NE, Seattle, WA 98195 USA..
    Bulla, Mattia
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden.;Stockholm Univ, Oskar Klein Ctr, Dept Astron, AlbaNova, SE-10691 Stockholm, Sweden..
    Singer, Leo P.
    NASA, Astrophys Sci Div, Goddard Space Flight Ctr, MC 661, Greenbelt, MD 20771 USA.;Univ Maryland, Joint Space Sci Inst, College Pk, MD 20742 USA..
    Optimizing serendipitous detections of kilonovae: cadence and filter selection2021In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 504, no 2, p. 2822-2831Article in journal (Refereed)
    Abstract [en]

    The rise of multimessenger astronomy has brought with it the need to exploit all available data streams and learn more about the astrophysical objects that fall within its breadth. One possible avenue is the search for serendipitous optical/near-infrared counterparts of gamma-ray bursts (GRBs) and gravitational-wave (GW) signals, known as kilonovae. With surveys such as the Zwicky Transient Facility (ZTF), which observes the sky with a cadence of similar to 3 d, the existing counterpart locations are likely to be observed; however, due to the significant amount of sky to explore, it is difficult to search for these fast-evolving candidates. Thus, it is beneficial to optimize the survey cadence for realtime kilonova identification and enable further photometric and spectroscopic observations. We explore how the cadence of wide field-of-view surveys like ZTF can be improved to facilitate such identifications. We show that with improved observational choices, e.g. the adoption of three epochs per night on a similar to nightly basis, and the prioritization of redder photometric bands, detection efficiencies improve by about a factor of two relative to the nominal cadence. We also provide realistic hypothetical constraints on the kilonova rate as a form of comparison between strategies, assuming that no kilonovae are detected throughout the long-term execution of the respective observing plan. These results demonstrate how an optimal use of ZTF increases the likelihood of kilonova discovery independent of GWs or GRBs, thereby allowing for a sensitive search with less interruption of its nominal cadence through Target of Opportunity programs.

  • 47. Alonso, D.
    et al.
    Bellini, E.
    Ferreira, P. G.
    Zumalacarregui, Miguel
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Sweden.
    Observational future of cosmological scalar-tensor theories2017In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 95, no 6, article id 063502Article in journal (Refereed)
    Abstract [en]

    The next generation of surveys will greatly improve our knowledge of cosmological gravity. In this paper we focus on how Stage IV photometric redshift surveys, including weak lensing and multiple tracers of the matter distribution and radio experiments combined with measurements of the cosmic microwave background will lead to precision constraints on deviations from general relativity. We use a broad subclass of Horndeski scalar-tensor theories to forecast the accuracy with which we will be able to determine these deviations and their degeneracies with other cosmological parameters. Our analysis includes relativistic effects, does not rely on the quasistatic evolution and makes conservative assumptions about the effect of screening on small scales. We define a figure of merit for cosmological tests of gravity and show how the combination of different types of surveys, probing different length scales and redshifts, can be used to pin down constraints on the gravitational physics to better than a few percent, roughly an order of magnitude better than present probes. Future cosmological experiments will be able to constrain

  • 48. Altfeder, Igor
    et al.
    Voevodin, Andrey A.
    Check, Michael H.
    Eichfeld, Sarah M.
    Robinson, Joshua A.
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Scanning Tunneling Microscopy Observation of Phonon Condensate2017In: Scientific Reports, E-ISSN 2045-2322, Vol. 7, article id 43214Article in journal (Refereed)
    Abstract [en]

    Using quantum tunneling of electrons into vibrating surface atoms, phonon oscillations can be observed on the atomic scale. Phonon interference patterns with unusually large signal amplitudes have been revealed by scanning tunneling microscopy in intercalated van der Waals heterostructures. Our results show that the effective radius of these phonon quasi-bound states, the real-space distribution of phonon standing wave amplitudes, the scattering phase shifts, and the nonlinear intermode coupling strongly depend on the presence of defect-induced scattering resonance. The observed coherence of these quasi-bound states most likely arises from phase-and frequency-synchronized dynamics of all phonon modes, and indicates the formation of many-body condensate of optical phonons around resonant defects. We found that increasing the strength of the scattering resonance causes the increase of the condensate droplet radius without affecting the condensate fraction inside it. The condensate can be observed at room temperature.

  • 49. Amendola, L.
    et al.
    Appleby, S.
    Avgoustidis, A.
    Bacon, D.
    Baker, T.
    Baldi, M.
    Bartolo, N.
    Blanchard, A.
    Bonvin, C.
    Borgani, S.
    Branchini, E.
    Burrage, C.
    Camera, S.
    Carbone, C.
    Casarini, L.
    Cropper, M.
    de Rham, C.
    Dietrich, J. P.
    Di Porto, C.
    Durrer, R.
    Ealet, A.
    Ferreira, P. G.
    Finelli, F.
    García-Bellido, J.
    Giannantonio, T.
    Guzzo, L.
    Heavens, A.
    Heisenberg, L.
    Heymans, C.
    Hoekstra, H.
    Hollenstein, L.
    Holmes, R.
    Hwang, Z.
    Jahnke, K.
    Kitching, T. D.
    Koivisto, Tomi
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden.
    Kunz, M.
    La Vacca, G.
    Linder, E.
    March, M.
    Marra, V.
    Martins, C.
    Majerotto, E.
    Markovic, D.
    Marsh, D.
    Marulli, F.
    Massey, R.
    Mellier, Y.
    Montanari, F.
    Mota, D. F.
    Nunes, N. J.
    Percival, W.
    Pettorino, V.
    Porciani, C.
    Quercellini, C.
    Read, J.
    Rinaldi, M.
    Sapone, D.
    Sawicki, I.
    Scaramella, R.
    Skordis, C.
    Simpson, F.
    Taylor, A.
    Thomas, S.
    Trotta, R.
    Verde, L.
    Vernizzi, F.
    Vollmer, A.
    Wang, Y.
    Weller, J.
    Zlosnik, T.
    Group, The Euclid Theory Working
    Cosmology and fundamental physics with the Euclid satellite2018In: Living Reviews in Relativity, E-ISSN 1433-8351, Vol. 21, no 1, article id 2Article in journal (Refereed)
    Abstract [en]

    Euclid is a European Space Agency medium-class mission selected for launch in 2020 within the cosmic vision 2015–2025 program. The main goal of Euclid is to understand the origin of the accelerated expansion of the universe. Euclid will explore the expansion history of the universe and the evolution of cosmic structures by measuring shapes and red-shifts of galaxies as well as the distribution of clusters of galaxies over a large fraction of the sky. Although the main driver for Euclid is the nature of dark energy, Euclid science covers a vast range of topics, from cosmology to galaxy evolution to planetary research. In this review we focus on cosmology and fundamental physics, with a strong emphasis on science beyond the current standard models. We discuss five broad topics: dark energy and modified gravity, dark matter, initial conditions, basic assumptions and questions of methodology in the data analysis. This review has been planned and carried out within Euclid’s Theory Working Group and is meant to provide a guide to the scientific themes that will underlie the activity of the group during the preparation of the Euclid mission.

  • 50. Amoretti, A.
    et al.
    Areán, D.
    Goutéraux, Blaise
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Musso, D.
    Effective holographic theory of charge density waves2018In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 97, no 8, article id 086017Article in journal (Refereed)
    Abstract [en]

    We use gauge/gravity duality to write down an effective low energy holographic theory of charge density waves. We consider a simple gravity model which breaks translations spontaneously in the dual field theory in a homogeneous manner, capturing the low energy dynamics of phonons coupled to conserved currents. We first focus on the leading two-derivative action, which leads to excited states with nonzero strain. We show that including subleading quartic derivative terms leads to dynamical instabilities of AdS2 translation invariant states and to stable phases breaking translations spontaneously. We compute analytically the real part of the electric conductivity. The model allows to construct Lifshitz-like hyperscaling violating quantum critical ground states breaking translations spontaneously. At these critical points, the real part of the dc conductivity can be metallic or insulating.

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