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  • 251.
    Ajello, M.
    et al.
    Clemson Univ, Kinard Lab Phys, Dept Phys & Astron, Clemson, SC 29634 USA..
    Baldini, L.
    Univ Pisa, I-56127 Pisa, Italy.;Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    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.
    Univ Politecn Bari, Dipartimento Fis M Merlin, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Blandford, R. D.
    Stanford Univ, Kavli Inst Particle Astrophys & Cosmol, WW Hansen Expt Phys Lab, 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, Kavli Inst Particle Astrophys & Cosmol, WW Hansen Expt Phys Lab, Dept Phys, Stanford, CA 94305 USA.;Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Bregeon, J.
    Univ Montpellier, CNRS IN2P3, Lab Univers & Particules Montpellier, F-34095 Montpellier, France..
    Bruel, P.
    CNRS IN2P3, Ecole Polytech, Lab Leprince Ringuet, F-91128 Palaiseau, France..
    Buehler, R.
    DESY, D-15738 Zeuthen, Germany..
    Cameron, R. A.
    Stanford Univ, Kavli Inst Particle Astrophys & Cosmol, WW Hansen Expt Phys Lab, Dept Phys, 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..
    Chiaro, G.
    INAF Ist Astrofis Spaziale & Fis Cosm Milano, Via E Bassini 15, I-20133 Milan, Italy..
    Ciprini, S.
    Agenzia Spaziale Italiana, Space Sci Data Ctr, Via Politecn, I-00133 Rome, Italy..
    Cohen-Tanugi, J.
    Univ Montpellier, CNRS IN2P3, Lab Univers & Particules Montpellier, F-34095 Montpellier, France..
    Costantin, D.
    Univ Padua, Dipartimento Fis & Astron G Galilei, I-35131 Padua, 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..
    Di Lalla, N.
    Univ Pisa, I-56127 Pisa, Italy.;Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    Di Mauro, M.
    Stanford Univ, Kavli Inst Particle Astrophys & Cosmol, WW Hansen Expt Phys Lab, Dept Phys, Stanford, CA 94305 USA..
    Di Venere, L.
    Univ Politecn Bari, Dipartimento Fis M Merlin, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Dominguez, A.
    Univ Complutense Madrid, Grp Altas Energias, E-28040 Madrid, Spain..
    Favuzzi, C.
    Univ Politecn Bari, Dipartimento Fis M Merlin, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Franckowiak, A.
    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.
    Univ Politecn Bari, Dipartimento Fis M Merlin, 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.
    Agenzia Spaziale Italiana, Space Sci Data Ctr, Via Politecn, I-00133 Rome, Italy.;Ist Nazl Fis Nucl, Sez Perugia, I-06123 Perugia, Italy..
    Giglietto, N.
    Univ Politecn Bari, Dipartimento Fis M Merlin, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Giordano, F.
    Univ Politecn Bari, Dipartimento Fis M Merlin, 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.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA.;NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Grenier, I. A.
    Univ Paris Diderot, Lab AIM, CEA IRFU, CNRS,Serv Astrophys,CEA Saclay, F-91191 Gif Sur Yvette, 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..
    Holt, C.
    Univ Maryland Baltimore Cty, Dept Phys, Baltimore, MD 21250 USA.;Univ Maryland Baltimore Cty, Ctr Space Sci & Technol, Baltimore, MD 21250 USA..
    Horan, D.
    CNRS IN2P3, Ecole Polytech, Lab Leprince Ringuet, F-91128 Palaiseau, France..
    Johannesson, G.
    Univ Iceland, Sci Inst, IS-107 Reykjavik, Iceland.;NORDITA, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden..
    Kocevski, D.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Kuss, M.
    Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    La Mura, G.
    Univ Padua, Dipartimento Fis & Astron G Galilei, I-35131 Padua, Italy..
    Larsson, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Li, J.
    Inst Space Sci CSICIEEC, Campus UAB,Carrer Magrans S-N, E-08193 Barcelona, Spain..
    Longo, F.
    Ist Nazl Fis Nucl, Sez Trieste, I-34127 Trieste, Italy.;Univ Trieste, Dipartimento Fis, I-34127 Trieste, Italy..
    Loparco, F.
    Univ Politecn Bari, Dipartimento Fis M Merlin, 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.
    Stanford Univ, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA..
    Manfreda, A.
    Univ Pisa, I-56127 Pisa, Italy..
    Mazziotta, M. N.
    Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Michelson, P. F.
    Stanford Univ, Kavli Inst Particle Astrophys & Cosmol, WW Hansen Expt Phys Lab, Dept Phys, Stanford, CA 94305 USA..
    Mizuno, T.
    Hiroshima Univ, Hiroshima Astrophys Sci Ctr, Higashihiroshima, Hiroshima 7398526, Japan..
    Monzani, M. E.
    Stanford Univ, Kavli Inst Particle Astrophys & Cosmol, WW Hansen Expt Phys Lab, Dept Phys, Stanford, CA 94305 USA..
    Morselli, A.
    Ist Nazl Fis Nucl, Sez Roma Tor Vergata, I-00133 Rome, Italy..
    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 Univers & Particules Montpellier, F-34095 Montpellier, France..
    Omodei, N.
    Stanford Univ, Kavli Inst Particle Astrophys & Cosmol, WW Hansen Expt Phys Lab, Dept Phys, Stanford, CA 94305 USA..
    Orienti, M.
    INAF Ist Radioastron, I-40129 Bologna, Italy..
    Orlando, E.
    Stanford Univ, Kavli Inst Particle Astrophys & Cosmol, WW Hansen Expt Phys Lab, Dept Phys, Stanford, CA 94305 USA..
    Paliya, V. S.
    Clemson Univ, Kinard Lab Phys, Dept Phys & Astron, Clemson, SC 29634 USA..
    Perkins, J. S.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Persic, M.
    Ist Nazl Fis Nucl, Sez Trieste, I-34127 Trieste, Italy.;Ist Nazl Astrofis, Osservatorio Astron 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 Univers & Particules Montpellier, F-34095 Montpellier, France..
    Principe, G.
    Friedrich Alexander Univ Erlangen Nurnberg, Erlangen Ctr Astroparticle Phys, Erwin Rommel Str 1, D-91058 Erlangen, Germany..
    Racusin, J. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Raino, S.
    Univ Politecn Bari, Dipartimento Fis M Merlin, 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, Kavli Inst Particle Astrophys & Cosmol, WW Hansen Expt Phys Lab, Dept Phys, 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, Kavli Inst Particle Astrophys & Cosmol, WW Hansen Expt Phys Lab, Dept Phys, 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..
    Sgro, C.
    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 Politecn Bari, Dipartimento Fis M Merlin, I-70126 Bari, Italy.;Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy..
    Tak, D.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Thayer, J. B.
    Stanford Univ, Kavli Inst Particle Astrophys & Cosmol, WW Hansen Expt Phys Lab, Dept Phys, Stanford, CA 94305 USA..
    Torres, D. F.
    ICREA, E-08010 Barcelona, Spain..
    Tosti, G.
    Univ Perugia, Dipartimento Fis, I-06123 Perugia, Italy..
    Valverde, J.
    CNRS IN2P3, Ecole Polytech, Lab Leprince Ringuet, F-91128 Palaiseau, France..
    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..
    Investigating the Nature of Late-time High-energy GRB Emission through Joint Fermi/Swift Observations2018Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 863, nr 2, artikel-id 138Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We use joint observations by the Swift X-ray Telescope (XRT) and the Fermi Large Area Telescope (LAT) of gamma-ray burst (GRB) afterglows to investigate the nature of the long-lived high-energy emission observed by Fermi LAT. Joint broadband spectral modeling of XRT and LAT data reveals that LAT nondetections of bright X-ray afterglows are consistent with a cooling break in the inferred electron synchrotron spectrum below the LAT and/or XRT energy ranges. Such a break is sufficient to suppress the high-energy emission so as to be below the LAT detection threshold. By contrast, LAT-detected bursts are best fit by a synchrotron spectrum with a cooling break that lies either between or above the XRT and LAT energy ranges. We speculate that the primary difference between GRBs with LAT afterglow detections and the nondetected population may be in the type of circumstellar environment in which these bursts occur, with late-time LAT detections preferentially selecting GRBs that occur in low wind-like circumburst density profiles. Furthermore, we find no evidence of high-energy emission in the LAT-detected population significantly in excess of the flux expected from the electron synchrotron spectrum fit to the observed X-ray emission. The lack of excess emission at high energies could be due to a shocked external medium in which the energy density in the magnetic field is stronger than or comparable to that of the relativistic electrons behind the shock, precluding the production of a dominant synchrotron self-Compton (SSC) component in the LAT energy range. Alternatively, the peak of the SSC emission could be beyond the 0.1-100 GeV energy range considered for this analysis.

  • 252.
    Ajello, M.
    et al.
    Clemson Univ, Dept Phys & Astron, Kinard Lab Phys, Clemson, SC 29634 USA..
    Ciprini, S.
    Ist Nazl Fis Nucl, Sez Roma Tor Vergata, I-00133 Rome, Italy.;Agenzia Spaziale Italiana, Space Sci Data Ctr, Via Politecn Snc, I-00133 Rome, Italy..
    Larsson, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. Oskar Klein Ctr Cosmoparticle Phys, AlbaNova, SE-10691 Stockholm, Sweden..
    Zaharijas, G.
    Univ Nova Gorica, Ctr Astrophys & Cosmol, Nova Gorica, Slovenia..
    The Fourth Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope: Data Release 32022Ingår i: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 263, nr 2, artikel-id 24Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An incremental version of the fourth catalog of active galactic nuclei (AGNs) detected by the Fermi Large Area Telescope is presented. This version (4LAC-DR3) derives from the third data release of the 4FGL catalog based on 12 yr of E > 50 MeV gamma-ray data, where the spectral parameters, spectral energy distributions (SEDs), yearly light curves, and associations have been updated for all sources. The new reported AGNs include 587 blazar candidates and four radio galaxies. We describe the properties of the new sample and outline changes affecting the previously published one. We also introduce two new parameters in this release, namely the peak energy of the SED high-energy component and the corresponding flux. These parameters allow an assessment of the Compton dominance, the ratio of the inverse-Compton to the synchrotron-peak luminosities, without relying on X-ray data.

  • 253.
    Ajello, M.
    et al.
    Clemson Univ, Kinard Lab Phys, Dept Phys & Astron, Clemson, SC 29634 USA..
    Johannesson, G.
    Univ Iceland, Inst Sci, IS-107 Reykjavik, Iceland.;;Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden..
    Larsson, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. Oskar Klein Ctr Cosmoparticle Phys, SE-10691 Stockholm, Sweden.;Dalarna Univ, Nat Sci, Sch Educ Hlth & Social Studies, SE-79188 Falun, Sweden..
    Pesce-Rollins, M.
    Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
    Zaharijas, G.
    Ist Nazl Fis Nucl, Sez Trieste, I-34127 Trieste, Italy.;Univ Trieste, Trieste, Italy.;Univ Nova Gorica, Ctr Astrophys & Cosmol, Nova Gorica, Slovenia..
    First Fermi-LAT Solar Flare Catalog2021Ingår i: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 252, nr 2, artikel-id 13Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present the first Fermi-Large Area Telescope (LAT) solar flare catalog covering the 24th solar cycle. This catalog contains 45 Fermi-LAT solar flares (FLSFs) with emission in the gamma-ray energy band (30 MeV-10 GeV) detected with a significance of >= 5 sigma over the years 2010-2018. A subsample containing 37 of these flares exhibits delayed emission beyond the prompt-impulsive hard X-ray phase, with 21 flares showing delayed emission lasting more than two hours. No prompt-impulsive emission is detected in four of these flares. We also present in this catalog observations of GeV emission from three flares originating from active regions located behind the limb of the visible solar disk. We report the lightcurves, spectra, best proton index, and localization (when possible) for all FLSFs. The gamma-ray spectra are consistent with the decay of pions produced by >300 MeV protons. This work contains the largest sample of high-energy gamma-ray flares ever reported and provides a unique opportunity to perform population studies on the different phases of the flare and thus allowing a new window in solar physics to be opened.

  • 254.
    Ajello, M.
    et al.
    Clemson Univ, Dept Phys & Astron, Kinard Lab Phys, Clemson, SC 29634 USA..
    Johannesson, Gudlaugur
    KTH, Centra, 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, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. 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 Winds2021Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 921, nr 2, artikel-id 144Artikel i tidskrift (Refereegranskat)
    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.

  • 255.
    Ajello, M.
    et al.
    Clemson Univ, Dept Phys & Astron, Kinard Lab Phys, Clemson, SC 29634 USA..
    Jóhannesson, Gudlaugur
    KTH, Centra, 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, Skolan för teknikvetenskap (SCI), Tillämpad fysik. 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 background2022Ingår i: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 376, nr 6592, s. 521-523Artikel i tidskrift (Refereegranskat)
    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.

  • 256.
    Ajello, M.
    et al.
    Clemson Univ, Dept Phys & Astron, Kinard Lab Phys, Clemson, SC 29634 USA..
    Jóhannesson, Gudlaugur
    KTH, Centra, 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 Telescope2019Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 883, nr 1, artikel-id 33Artikel i tidskrift (Refereegranskat)
    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.

  • 257.
    Ajello, Marco
    et al.
    Department of Physics and Astronomy, Clemson University, Kinard Lab of Physics, Clemson, SC 29634-0978, USA.
    Johannesson, Gudni
    KTH, Centra, 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, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. 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 Winds2022Ingår i: 37th International Cosmic Ray Conference, ICRC 2021, Sissa Medialab Srl , 2022, artikel-id 596Konferensbidrag (Refereegranskat)
    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.

  • 258.
    Akhmedov, Evgeny Kh
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Neutrino oscillations: Theory and phenomenology2006Ingår i: NEUTRINO - Proc. Int. Conf. Neutrino Phys. Astrophys., 2006, s. 16-22Konferensbidrag (Refereegranskat)
    Abstract [en]

    A brief overview of selected topics in the theory and phenomenology of neutrino oscillations is given. These include: oscillations in vacuum and in matter; phenomenology of 3-flavour neutrino oscillations; CP and T violation in neutrino oscillations in vacuum and in matter; matter effects on νμ ↔ ντ oscillations; parametric resonance in neutrino oscillations inside the earth; oscillations below and above the MSW resonance; unsettled issues in the theory of neutrino oscillations.

  • 259. Akrami, Y.
    et al.
    Ashdown, M.
    Aumont, J.
    Baccigalupi, C.
    Ballardini, M.
    Banday, A. J.
    Barreiro, R. B.
    Bartolo, N.
    Basak, S.
    Benabed, K.
    Bernard, J. -P
    Bersanelli, M.
    Bielewicz, P.
    Bond, J. R.
    Borrill, J.
    Bouchet, F. R.
    Boulanger, F.
    Bracco, Andrea
    Nordita SU.
    Bucher, M.
    Burigana, C.
    Calabrese, E.
    Cardoso, J. -F
    Carron, J.
    Chiang, H. C.
    Combet, C.
    Crill, B. P.
    de Bernardis, P.
    de Zotti, G.
    Delabrouille, J.
    Delouis, J. -M
    Di Valentino, E.
    Dickinson, C.
    Diego, J. M.
    Ducout, A.
    Dupac, X.
    Efstathiou, G.
    Elsner, F.
    Ensslin, T. A.
    Falgarone, E.
    Fantaye, Y.
    Ferriere, K.
    Finelli, F.
    Forastieri, F.
    Frailis, M.
    Fraisse, A. A.
    Franceschi, E.
    Frolov, A.
    Galeotta, S.
    Galli, S.
    Ganga, K.
    Genova-Santos, R. T.
    Ghosh, T.
    Gonzalez-Nuevo, J.
    Gorski, K. M.
    Gruppuso, A.
    Gudmundsson, Jon Tomas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Rymd- och plasmafysik.
    Guillet, V.
    Handley, W.
    Hansen, F. K.
    Herranz, D.
    Huang, Z.
    Jaffe, A. H.
    Jones, W. C.
    Keihanen, E.
    Keskitalo, R.
    Kiiveri, K.
    Kim, J.
    Krachmalnicoff, N.
    Kunz, M.
    Kurki-Suonio, H.
    Lamarre, J. -M
    Lasenby, A.
    Le Jeune, M.
    Levrier, F.
    Liguori, M.
    Lilje, P. B.
    Lindholm, V.
    Lopez-Caniego, M.
    Lubin, P. M.
    Ma, Y. -Z
    Macias-Perez, J. F.
    Maggio, G.
    Maino, D.
    Mandolesi, N.
    Mangilli, A.
    Martin, P. G.
    Martinez-Gonzalez, E.
    Matarrese, S.
    McEwen, J. D.
    Meinhold, P. R.
    Melchiorri, A.
    Migliaccio, M.
    Miville-Deschenes, M. -A
    Molinari, D.
    Moneti, A.
    Montier, L.
    Morgante, G.
    Natoli, P.
    Pagano, L.
    Paoletti, D.
    Pettorino, V.
    Piacentini, F.
    Polenta, G.
    Puget, J. -L
    Rachen, J. P.
    Reinecke, M.
    Remazeilles, M.
    Renzi, A.
    Rocha, G.
    Rosset, C.
    Roudier, G.
    Rubino-Martin, J. A.
    Ruiz-Granados, B.
    Salvati, L.
    Sandri, M.
    Savelainen, M.
    Scott, D.
    Soler, J. D.
    Spencer, L. D.
    Tauber, J. A.
    Tavagnacco, D.
    Toffolatti, L.
    Tomasi, M.
    Trombetti, T.
    Valiviita, J.
    Vansyngel, F.
    Van Tent, B.
    Vielva, P.
    Villa, F.
    Vittorio, N.
    Wehus, I. K.
    Zacchei, A.
    Zonca, A.
    Planck 2018 results: XI. Polarized dust foregrounds2020Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 641, artikel-id A11Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The study of polarized dust emission has become entwined with the analysis of the cosmic microwave background (CMB) polarization in the quest for the curl-like B-mode polarization from primordial gravitational waves and the low-multipole E-mode polarization associated with the reionization of the Universe. We used the new Planck PR3 maps to characterize Galactic dust emission at high latitudes as a foreground to the CMB polarization and use end-to-end simulations to compute uncertainties and assess the statistical significance of our measurements. We present PlanckEE, BB, and TE power spectra of dust polarization at 353 GHz for a set of six nested high-Galactic-latitude sky regions covering from 24 to 71% of the sky. We present power-law fits to the angular power spectra, yielding evidence for statistically significant variations of the exponents over sky regions and a difference between the values for the EE and BB spectra, which for the largest sky region are alpha (EE)=-2.42 +/- 0.02 and alpha (BB)=-2.54 +/- 0.02, respectively. The spectra show that the TE correlation and E/B power asymmetry discovered by Planck extend to low multipoles that were not included in earlier Planck polarization papers due to residual data systematics. We also report evidence for a positive TB dust signal. Combining data from Planck and WMAP, we have determined the amplitudes and spectral energy distributions (SEDs) of polarized foregrounds, including the correlation between dust and synchrotron polarized emission, for the six sky regions as a function of multipole. This quantifies the challenge of the component-separation procedure that is required for measuring the low-l reionization CMB E-mode signal and detecting the reionization and recombination peaks of primordial CMB B modes. The SED of polarized dust emission is fit well by a single-temperature modified black-body emission law from 353 GHz to below 70 GHz. For a dust temperature of 19.6 K, the mean dust spectral index for dust polarization is beta (P)(d) = 1.53 +/- 0.02 beta d P = 1.53 +/- 0.02 . The difference between indices for polarization and total intensity is beta (P)(d)-beta (I)(d) = 0.05 +/- 0.03 beta d P - beta d I =0.05 +/- 0.03 . By fitting multi-frequency cross-spectra between Planck data at 100, 143, 217, and 353 GHz, we examine the correlation of the dust polarization maps across frequency. We find no evidence for a loss of correlation and provide lower limits to the correlation ratio that are tighter than values we derive from the correlation of the 217- and 353 GHz maps alone. If the Planck limit on decorrelation for the largest sky region applies to the smaller sky regions observed by sub-orbital experiments, then frequency decorrelation of dust polarization might not be a problem for CMB experiments aiming at a primordial B-mode detection limit on the tensor-to-scalar ratio r similar or equal to 0.01 at the recombination peak. However, the Planck sensitivity precludes identifying how difficult the component-separation problem will be for more ambitious experiments targeting lower limits on r.

  • 260.
    Akrami, Yashar
    et al.
    KTH, Centra, 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, Centra, 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, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Bimetric gravity is cosmologically viable2015Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 748, s. 37-44Artikel i tidskrift (Refereegranskat)
    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.

  • 261. Akrami, Yashar
    et al.
    Koivisto, Tomi S.
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Solomon, Adam R.
    The nature of spacetime in bigravity: Two metrics or none?2015Ingår i: General Relativity and Gravitation, ISSN 0001-7701, E-ISSN 1572-9532, Vol. 47, nr 1, s. 1838-Artikel i tidskrift (Refereegranskat)
    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.

  • 262.
    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, Centra, 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 binaries2021Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 507, nr 4, s. 5507-5522Artikel i tidskrift (Refereegranskat)
    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.

  • 263.
    Alday, Juan
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Roth, Lorenz
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Ivchenko, Nickolay
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Retherford, Kurt D.
    Becker, Tracy M.
    Molyneux, Philippa
    Saur, Joachim
    New constraints on Ganymede's hydrogen corona: Analysis of Lyman-alpha emissions observed by HST/STIS between 1998 and 20142017Ingår i: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 148, s. 35-44Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Far-ultraviolet observations of Ganymede's atmospheric emissions were obtained with the Space Telescope Imaging Spectrograph (STIS) onboard of the Hubble Space Telescope (HST) on several occasions between 1998 and 2014. We analyze the Lyman-alpha emission from four HST campaigns in order to constrain the abundance and variation of atomic hydrogen in Ganymede's atmosphere. We apply a forward model that estimates surface reflection and resonant scattering in an escaping corona of the solar Lyman-alpha flux, taking into account the effects of the hydrogen in the interplanetary medium. The atmospheric emissions around Ganymede's disk derived for the observations taken between 1998 and 2011 are consistent with a hydrogen corona in the density range of (5-8) x 10(3) cm(-3) at the surface. The hydrogen density appears to be generally stable in that period. In 2014, Ganymede's corona brightness is approximately 3 times lower during two observations of Ganymede's trailing hemisphere and hardly detectable at all during two observations of the leading hemisphere. We also investigate extinction of Ganymede's coronal emissions in the Earth's upper atmosphere or geocorona. For small Doppler shifts, resonant scattering in the geocorona of the moon corona emissions can effectively reduce the brightness observed by HST. In the case of the 2014 leading hemisphere observations, an estimated extinction of 80% might explain the non-detection of Ganymede's hydrogen corona. Geocoronal extinction might also explain a previously detected hemispheric difference from Callisto's hydrogen corona.

  • 264.
    Alessio, Francesco
    et al.
    Nordita SU.
    Di Vecchia, Paolo
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Radiation reaction for spinning black-hole scattering2022Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 832, artikel-id 137258Artikel i tidskrift (Refereegranskat)
    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.

  • 265.
    Alfvén, Hannes
    Dept Applied Physics and Information Science, University of California, San Diego, La Jolla, CA 92093, USA.
    3 revolutions in cosmical science from the telescope to the Sputnik1989Ingår i: Annals of the New York Academy of Sciences, ISSN 0077-8923, E-ISSN 1749-6632, Vol. 571, s. 649-662Artikel i tidskrift (Refereegranskat)
  • 266.
    Alfvén, Hannes
    Dept Applied Physics and Information Science, University of California, San Diego, La Jolla, CA 92093, USA.
    Annihilation model of quasi-stellar objects1979Ingår i: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 64, nr 2, s. 401-419Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The possibility that annihilation is a major source of energy in cosmic physics is discussed. Since Klein suggested that the Universe might be matter-antimatter symmetric over two decades ago, there have been a significant number of papers developing the consequences of this view. These, however, have been largely ignored in the general literature. There have also been a number of papers claiming to prove that there cannot be antimatter anywhere in the observable Universe. In the first part of this paper an assessment of the differing views is given, and it is shown that none of the arguments against antimatter is convincing. The existence of antimatter is not in conflict with any observational fact. The reason for the negative attitude towards the existence of antimatter seems to be that this view is in conflict with a number of speculative but ‘generally accepted’ theories. However, recent magnetospheric and heliospheric research, includingin situ measurements of cosmic plasmas, is now drastically changing cosmic plasma physics in a way that leads to growing scepticism about quite a few of the speculative theories.

    An attempt is made to develop a simple phenomenological model of QSOs based on star-antistar collisions. This model can account for such basic observational properties as the acceleration to very large (non-cosmological) velocities, the existence of broad emission lines, and at the same time narrow absorption lines with different redshifts. The absence of blueshifts is also explained. The model predicts that relatively young QSOs should be at cosmological distances whereas the old ones may very well be much closer to us than indicated by their redshift.

  • 267.
    Alfvén, Hannes
    KTH, Tidigare Institutioner (före 2005).
    Annihilation Model of the QSOs1979Rapport (Övrigt vetenskapligt)
    Ladda ner fulltext (pdf)
    fulltext
  • 268.
    Alfvén, Hannes
    KTH, Tidigare Institutioner (före 2005). Dept Applied Physics and Information Science, University of California, San Diego, La Jolla, CA 92093, USA.
    Cosmogony as an extrapolation of magnetospheric research1984Ingår i: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 39, nr 1-2, s. 65-90Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    A theory of the origin and evolution of the Solar System (Alfvén and Arrhenius, 1975, 1976) which considered electromagnetic forces and plasma effects is revised in the light of new information supplied by space research. In situ measurements in the magnetospheres and solar wind have changed our views of basic properties of cosmic plasmas. These results can be extrapolated both outwards in space, to interstellar clouds, and backwards in time, to the formation of the solar system. The first extrapolation leads to a revision of some cloud properties which are essential for the early phases in the formation of stars and solar nebulae. The latter extrapolation makes possible to approach the cosmogonic processes by extrapolation of (rather) well-known magnetospheric phenomena.

    Pioneer-Voyager observations of the Saturnian rings indicate that essential parts of their structure are ‘fossils’ from cosmogonic times. By using detailed information from these space missions, it seems possible to reconstruct certain events 4–5 billion years ago with an accuracy of a few percent. This will cause a change in our views of the evolution of the solar system.

  • 269.
    Alfvén, Hannes
    KTH, Tidigare Institutioner (före 2005).
    Cosmology in the plasma universe1988Ingår i: Laser and particle beams (Print), ISSN 0263-0346, E-ISSN 1469-803X, Vol. 6, s. 389-398Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Space observations have opened the spectral regions of X-rays and γ-rays, which are produced by plasma processes. The Plasma Universe derived from observations in these regions is drastically different from the now generally accepted ‘Visual Light Universe’ based on visual light observations alone. Historically this transition can be compared only to the transition from the the geocentric to the heliocentric cosmology.

    The purpose of this paper is to discuss what criteria a cosmological theory must satisfy in order to be acceptable in the Plasma Universe.

  • 270.
    Alfvén, Hannes
    KTH, Tidigare Institutioner (före 2005).
    Cosmology: Myth or science1976Ingår i: La Recherche (Imprimé), ISSN 0029-5671, E-ISSN 1625-9955, Vol. 7, nr 69, s. 610-616Artikel i tidskrift (Refereegranskat)
  • 271.
    Alfvén, Hannes
    KTH, Tidigare Institutioner (före 2005).
    Cosmology: Myth or science?1992Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 20, nr 6, s. 590-600Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper examines critically the history of cosmology and presents ideas that lay the foundation of the plasma universe.

  • 272.
    Alfvén, Hannes
    KTH, Tidigare Institutioner (före 2005). Dept Applied Physics and Information Science, University of California, San Diego, La Jolla, CA 92093, USA.
    Cosmology: Myth or science1984Ingår i: Journal of astrophysics and astronomy, ISSN 0250-6335, E-ISSN 0973-7758, Vol. 5, nr 1, s. 79-98Artikel i tidskrift (Refereegranskat)
  • 273.
    Alfvén, Hannes
    KTH, Tidigare Institutioner (före 2005).
    Double Radio Sources and the New Approach to Cosmic Plasma Physics1977Rapport (Övrigt vetenskapligt)
    Ladda ner fulltext (pdf)
    fulltext
  • 274.
    Alfvén, Hannes
    KTH, Tidigare Institutioner (före 2005).
    Double radio-sources and new approach to cosmical plasma physics1978Ingår i: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 54, nr 2, s. 279-292Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The methodology of cosmic plasma physics is discussed. It is very hazardous to try to describe plasma phenomena by theories which have not been carefully tested experimentally. One present approach is to rely on laboratory measurements andin situ measurements in the magnetosphere and heliosphere, and to approach galactic phenomena by scaling up the wellknown phenomena to galactic dimensions. A summary is given of laboratory investigations of electric double layers, a phenomenon which is known to be very important in laboratory discharges. A summary is also given of thein situ measurements in the magnetosphere by which the importance of electric double layers in the Earth's surrounding is established. The scaling laws between laboratory and magnetospheric double layers are studied. The successful scaling between laboratory and magnetospheric phenomena encourages an extrapolation to heliospheric phenomena. A further extrapolation to galactic phenomena leads to a theory of double radio sources.

    In analogy with the Sun which, acting as a homopolar inductor, energizes the heliospheric current system, a rotating magnetized galaxy should produce a similar current system. From analogy with laboratory and magnetospheric current systems it is argued that the galactic current might produce double layers where a large energy dissipation takes place. This leads to a theory of the double radio sources which, within the necessary wide limits of uncertainty, is quantitatively reconcilable with observations.

  • 275.
    Alfvén, Hannes
    Dept Applied Physics and Information Science, University of California, San Diego, La Jolla, CA 92093, USA.
    Filamentary structures1986Ingår i: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 231, nr 4741, s. 907-908Artikel i tidskrift (Refereegranskat)
  • 276.
    Alfvén, Hannes
    University of California San Diego, Dept Applied Physics and Information Science, San Diego, CA 92093.
    Frozen-in field lines and field-line reconnection1976Ingår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 81, nr 22, s. 4019-4021Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is shown that ‘frozen-in magnetic field lines’ and ‘magnetic field-line reconnection’ are unnecessary and often misleading concepts.

  • 277.
    Alfvén, Hannes
    KTH, Tidigare Institutioner (före 2005).
    Has the Universe an Origin?1988Rapport (Övrigt vetenskapligt)
    Ladda ner fulltext (pdf)
    fulltext
  • 278.
    Alfvén, Hannes
    KTH, Tidigare Institutioner (före 2005).
    Hubble Expansion in a Euclidean Framework1979Rapport (Övrigt vetenskapligt)
    Ladda ner fulltext (pdf)
    fulltext
  • 279.
    Alfvén, Hannes
    KTH, Tidigare Institutioner (före 2005).
    Hubble expansion in a Euclidean framework1979Ingår i: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 66, nr 1, s. 23-37Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    There now seems to be strong evidence for a non-cosmological interpretation of the QSO redshift — in any case, so strong that it is of interest to investigate the consequences. The purpose of this paper is to construct a model of the Hubble expansion which is as far as possible from the conventional Big Bang model without coming in conflict with any well-established observational results (while introducing no new laws of physics). This leads to an essentially Euclidean metagalactic model (see Table I) with very little mass outside one-third or half of the Hubble radius. The total kinetic energy of the Hubble expansion need only to be about 5% of the rest mass energy.

    Present observations support backwards in time extrapolation of the Hubble expansion to a ‘minimum size galaxy’R  m , which may have any value in 0<R  m <4×1026 cm. Other arguments speak in favor of a size close to the upper value, sayR  m =1026 cm (Table II). As this size is probably about 100 times the Schwarzschild limit, an essentially Euclidean description is allowed. The kinetic energy of the Hubble expansion may derive from an intense QSO-like activity in the minimum size metagalaxy, with an energy release corresponding to the annihilation of a few solar masses per galaxy per year.

    Some of the conclusions based on the Big Bang hypothesis are criticized and in several cases alternative interpretations are suggested. A comparison between the Euclidean and the conventional models is given in Table III.

  • 280.
    Alfvén, Hannes
    KTH, Tidigare Institutioner (före 2005).
    Memoirs of a dissident scientist1988Ingår i: American Scientist, ISSN 0003-0996, E-ISSN 1545-2786, Vol. 76, nr 3, s. 249-251Artikel i tidskrift (Refereegranskat)
  • 281.
    Alfvén, Hannes
    KTH, Tidigare Institutioner (före 2005).
    Observations and cosmology1979Ingår i: Chemiker-Zeitung, ISSN 0009-2894, Vol. 103, nr 10, s. 334-336Artikel i tidskrift (Övrigt vetenskapligt)
  • 282.
    Alfvén, Hannes
    KTH, Tidigare Institutioner (före 2005).
    On Hierarchical Cosmology1982Rapport (Övrigt vetenskapligt)
    Ladda ner fulltext (pdf)
    fulltext
  • 283.
    Alfvén, Hannes
    KTH, Tidigare Institutioner (före 2005).
    On hierarchical cosmology1983Ingår i: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 89, nr 2, s. 313-324Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Progress in laboratory studies of plasmas and in the methods of transferring the results to cosmic conditions, together within situ measurements in the magnetospheres, are now causing a ‘paradigm transition’ in cosmic plasma physics. This involves an introduction ofinhomogeneous models with double layers, filaments, ‘cell walls’, etc.

    Independently, it has been discovered that the mass distribution in the universe is highly inhomogeneous; indeed,hierarchical. According to de Vaucouleurs, the escape velocity of cosmic structures is 102–103 times below the Laplace-Schwarzschild limit, leaving avoid region which is identified as a key problem in cosmology.

    It is shown that a plasma instability in the dispersed medium of the structures may produce this void and, hence, explain the hierarchical structure. The energy which is necessary may derive either from gravitation or from annihilation caused by a breakdown of cell walls. The latter alternative is discussed in detail. It leads to a ‘Fireworks Model’ of the evolution of the metagalaxy.

    It is questioned whether the homogeneous four-dimensional big bang model can survive in an universe which is inhomogeneous and three-dimensional.

  • 284.
    Alfvén, Hannes
    Dept Applied Physics and Information Science, University of California, San Diego, La Jolla, CA 92093, USA.
    Origin of cosmic magnetic-fields1979Ingår i: Physics of the Earth and Planetary Interiors, ISSN 0031-9201, E-ISSN 1872-7395, Vol. 20, nr 2-4, s. 185-191Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A summary is given of the reasons why an understanding of cosmic hydromagnetic phenomena is impossible without describing them explicitly by electric currents. This applies also to the production of cosmic magnetic fields. The purpose of the paper is to demonstrate that a simple translation from the traditional magnetic field description to a current description gives important new aspects of cosmical electrodynamics, including a new approach to the production of magnetic fields.

    One of the results is that the kink-instability of electric currents is found to be the basic physical phenomenon responsible for magnetic flux generation in cosmical physics. Laboratory plasma experiments demonstrate the existence of a simple mechanism for flux amplification, and it seems obvious that the same mechanism should work also under cosmical conditions.

    A simple model is discussed. We start from a poloidal magnetic field (which may be extremely weak). Differential motions change the field configuration which means that kinetic energy is transferred into magnetic energy of induced toroidal fields. The currents associated with these get unstable when the toroidal energy exceeds the poloidal energy resulting in an amplification of the original poloidal field.

    This simple process of transfer of kinetic energy into poloidal magnetic energy is probably the main mechanism for magnetic flux generation in low density cosmic plasmas. In view of the serious difficulties of planetary dynamo theories, attempts should be made to develop it into a theory of the magnetization of celestial bodies.

  • 285.
    Alfvén, Hannes
    KTH, Tidigare Institutioner (före 2005).
    Paradigm Transition in Cosmic Plasma Physics1982Rapport (Övrigt vetenskapligt)
    Ladda ner fulltext (pdf)
    fulltext
  • 286.
    Alfvén, Hannes
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Relations between cosmic and laboratory plasma physics1975Ingår i: Annals of the New York Academy of Sciences, ISSN 0077-8923, E-ISSN 1749-6632, Vol. 257, nr AUG22, s. 179-188Artikel i tidskrift (Refereegranskat)
  • 287.
    Alfvén, Hannes
    KTH, Tidigare Institutioner (före 2005).
    Rymdforskningen och vår världsbild1982Rapport (Övrigt vetenskapligt)
    Ladda ner fulltext (pdf)
    fulltext
  • 288.
    Alfvén, Hannes
    KTH, Tidigare Institutioner (före 2005). Dept Applied Physics and Information Science, University of California, San Diego, La Jolla, CA 92093, USA.
    Solar-system history as recorded in the Saturnian ring structure1983Ingår i: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 97, nr 1, s. 79-94Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The paper is based on Holberg's analysis of the Voyager photographs in both reflected and transparent light, combined with occultation data of stars seen through the rings.

    Besides rapidly varying phenomena (spokes, braided ring, etc.), which according to Mendis are due to gravito-electromagnetic effects, the ring consists of abulk structure, a fine structure, and also ahyperfine structure, showing more than 10000 ringlets.

    The large number of ringlets can be explained by the Baxter-Thompson ‘negative diffusion’. This gives the ringlets a stability which makes it possible to interprete them as ‘fossils’, which originated at cosmogonic times.

    It is shown that thebulk structure can be explained by the combined ‘cosmogonic shadows’ of Mimas, the co-orbiting satellites, and the Shepherd satellites. This structure originated at the transition from the plasma phase to the planetesimal phase (which probably took place 4–5×109 y ago).

    Further, Holberg has discovered that the shadows are not simple void region but exhibit a certain characteristic ‘signature’. This is not yet understood theoretically.

    Parts of thefine structure are explained by Holberg as resonances with the satellites. Parts are here interpreted as cosmogonic shadow effects. However, there are a number of ringlets which can neither be explained by cosmogonic nor by resonance effects.

    The most important conclusion is that an analysis of the ring data is likely to lead to areconstruction of the plasma-planetesimal transition with an accuracy of a few percent.

  • 289.
    Alfvén, Hannes
    KTH, Tidigare Institutioner (före 2005).
    The plasma universe1986Ingår i: Physics today, ISSN 0031-9228, E-ISSN 1945-0699, Vol. 39, nr 9, s. 22-27Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For millennia we have based our views of the universe on observations in the narrow visual octave of the electromagnetic spectrum, 400–800 nm, supplemented during the last half‐century by infrared and radio observations. During the last decade, however, space research has opened the full spectrum, including the entire infrared region and the ultraviolet, x‐ray and γ‐ray regions (see the photo on the cover and figure 1).

  • 290.
    Alfvén, Hannes
    et al.
    KTH, Tidigare Institutioner (före 2005).
    Arrhenius, Gustaf
    Cosmogonic Scenario1985Rapport (Övrigt vetenskapligt)
    Ladda ner fulltext (pdf)
    fulltext
  • 291.
    Alfvén, Hannes
    et al.
    KTH, Tidigare Institutioner (före 2005).
    Axnäs, Ingvar
    KTH, Tidigare Institutioner (före 2005).
    Brenning, Nils
    KTH, Tidigare Institutioner (före 2005).
    Lindqvist, Per-Arne
    KTH, Tidigare Institutioner (före 2005).
    Voyager saturnian ring measurements and the early history of the solar-system1986Ingår i: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 34, nr 2, s. 145-154Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mass distribution in the Saturnian ring system is investigated and compared with predictions from the plasma cosmogony. According to this theory, the matter in the rings has once been in the form of a magnetized plasma, in which the gravitation is balanced partly by the centrifugal force and partly by the electromagnetic forces. As the plasma is neutralized, the electromagnetic forces disappear and the matter can be shown to fall in to of the original saturnocentric distance. This causes the so called “cosmogonic shadow effect”, which has been demonstrated earlier for the asteroidal belt and in the large scale structure of the Saturnian ring system.

    The relevance of the cosmogonic shadow effect is investigated for parts of the fine structures of the Saturnian ring system. It is shown that many structures of the present ring system can be understood as shadows and antishadows of cosmogonic origin. These appear in the form of double rings centered around a position a factor 0.64 (slightly less than) closer to Saturn than the causing feature. Voyager data agree with an accuracy better than 1%.

  • 292.
    Alfvén, Hannes
    et al.
    KTH, Tidigare Institutioner (före 2005).
    Carlqvist, Per
    KTH, Tidigare Institutioner (före 2005).
    Inter-stellar clouds and formation of stars1978Ingår i: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 55, nr 2, s. 487-509Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Part I gives a survey of the drastic revision of cosmic plasma physics which is precipitated by the exploration of the magnetosphere throughin situ measurements. The ‘pseudo-plasma formalism’, which until now has almost completely dominated theoretical astrophysics, must be replaced by an experimentally based approach involving the introduction of a number of neglected plasma phenomena, such as electric double layers, critical velocity, and pinch effect. The general belief that star light is the main ionizer is shown to be doubtful; hydromagnetic conversion of gravitational and kinetic energy may often be much more important.

    In Part II the revised plasma physics is applied to dark clouds and star formation. Magnetic fields do not necessarily counteract the contraction of a cloud; they may just as well ‘pinch’ the cloud. Magnetic compression may be the main mechanism for forming interstellar clouds and keeping them together.

    Part III treats the formation of stars in a dusty cosmic plasma cloud. Star formation is due to an instability, but it is very unlikely that it has anything to do with the Jeans instability. A reasonable mechanism is that the sedimentation of ‘dust’ (including solid bodies of different size) is triggering off a gravitationally assisted accretion. A ‘stellesimal’ accretion analogous to the planetesimal accretion leads to the formation of a star surrounded by a very low density hollow in the cloud. Matter falling in from the cloud towards the star is the raw material for the formation of planets and satellites.

    The study of the evolution of a dark cloud leads to a scenario of planet formation which is reconcilable with the results obtained from studies based on solar system data. This means that the new approach to cosmical plasma physics discussed in Part I logically leads to a consistent picture of the evolution of dark clouds and the formation of solar systems.

  • 293.
    Alfvén, Hannes
    et al.
    Dept Applied Physics and Information Science, University of California, San Diego, La Jolla, CA 92093, USA.
    Luhmann Jr., N. C.
    University of California, Los Angeles, California.
    Physics News in 19841985Ingår i: Physics today, ISSN 0031-9228, E-ISSN 1945-0699, Vol. 38, nr 11, s. 144-144Artikel i tidskrift (Refereegranskat)
  • 294.
    Alibakhshikenari, Mohammad
    et al.
    Univ Carlos III Madrid, Dept Signal Theory & Commun, Madrid 28911, Spain..
    Virdee, Bal S.
    London Metropolitan Univ, Ctr Commun Technol, London, England..
    Vadala, Valeria
    Univ Milano Bicocca, Dept Phys, I-20126 Milan, Italy..
    Dalarsson, Mariana
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Gomez, Maria Elena de Cos
    Univ Oviedo, TSC Elect Engn Dept, Gijon 33203, Spain..
    Alharbi, Abdullah G.
    Jouf Univ, Fac Engn, Dept Elect Engn, Sakaka 42421, Saudi Arabia..
    Burokur, Shah Nawaz
    Univ Paris Nanterre, UPL, LEME, F-92410 Ville Davray, France..
    Aissa, Sonia
    Inst Natl Rech Sci INRS, Montreal, PQ H5A 1K6, Canada..
    Dayoub, Iyad
    Univ Lille, Univ Polytech Hauts France, CNRS, Inst Elect Microelect & Nanotechnol IEMN,ISEN,Cent, F-59313 Valenciennes, France.;Univ Roma Tor Vergata, Elect Engn Dept, Via Politecn 1, I-00133 Valenciennes, Italy..
    Falcone, Francisco
    Univ Publ Navarra, Dept Elect Elect & Commun Engn, Pamplona 31006, Spain.;Inst Smart Cities, Publ Univ Navarre, Pamplona 31006, Spain.;Tecnol Monterrey, Sch Engn & Sci, Monterrey, Mexico..
    Limiti, Ernesto
    Broadband 3-D shared aperture high isolation nine-element antenna array for on-demand millimeter-wave 5G applications2022Ingår i: Optik (Stuttgart), ISSN 0030-4026, E-ISSN 1618-1336, Vol. 267, artikel-id 169708Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The paper presents the results of a novel 3-D shared aperture 3 x 3 matrix antenna-array for 26 GHz band 5 G wireless networks. Radiation elements constituting the array are hexagonal-shaped patches that are elevated above the common dielectric substrate by 3.35 mm and excited through a metallic rod of 0.4 mm diameter. The rod protrudes through the substrate of 0.8 mm thickness. It is shown that by isolating each radiating element in the array with a wall suppresses unwanted electromagnetic (EM) wave interactions, resulting in improvement in the antenna's impedance matching and radiation characteristics. Moreover, the results show that by embedding hexagonalshaped slots in the patches improve the antenna's gain and radiation efficiency performance. The subwavelength length slots in the patches essentially transform the radiating elements to exhibit metasurface characteristics when the array is illuminated by EM-waves. The proposed array structure has an average gain and radiation efficiency of 20 dBi and 93%, respectively, across 24.0-28.4 GHz. The isolation between its radiation elements is greater than 22 dB. Compared to the unslotted array the improvement in isolation between radiating elements is greater than 11 dB, and the gain and efficiency are better than 10.5 dBi, and 25%, respectively. The compact array has a fractional bandwidth of 16% and a form factor of 20 x 20 x 3.35 mm(3).

  • 295.
    Alm, Love
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Li, Bin
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Karlsson, Tomas
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Statistical altitude distribution of the auroral density cavity2015Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, nr 2, s. 996-1006Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The statistical altitude distribution of auroral density cavities located between 3.0 and 6.5 R-E is investigated using in situ observations from flux tubes exhibiting auroral acceleration. The locations of the observations are described using a pseudo altitude derived from the distribution of the parallel potential drop above and below the satellite. The upper edge of the auroral acceleration region is observed between 4.375 and 5.625 R-E. Above 6.125 R-E, none of the events exhibit precipitating inverted V electrons, though the upward ion beam can be observed. This indicates that the satellites are located inside the same flux tube as, but above, the auroral acceleration region. The electron density decreases as we move higher into the acceleration region. The spacecraft potential continues to decrease once above the acceleration region, indicating that the density cavity extends above the acceleration region. From 3.0 to 4.375 R-E the pseudo altitude increases by 0.20 per R-E, consistent with a distributed parallel electric field. Between 4.375 and 5.625 R-E the pseudo altitude increases weakly, by 0.01 per R-E, due to an increasing number of events per altitude bin, which are occurring above the acceleration region. Above 5.625 R-E the pseudo altitude increases by 0.28 per R-E, due to a rapid increase in the number of events per altitude bin occurring above the acceleration region, indicating that the remaining parallel potential drop is concentrated in a narrow region at the upper edge of the acceleration region, rather than in a distributed parallel electric field.

  • 296.
    Alm, Love
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran T.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Karlsson, Tomas
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    In situ observations of density cavities extending above the auroral acceleration region2014Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 119, nr 7, s. 5286-5294Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The uppermost part of a stable potential structure in the auroral acceleration region was studied using simultaneous observations of Cluster satellites C1 and C3. Both satellites observe a monotonically decreasing electron density as they ascend through the auroral acceleration region. As C1 exits the top of the auroral acceleration region, the electron densities continue to decrease, and the minimum electron density is reached 14 km above the upper edge of the auroral acceleration region. The electron density does not return to noncavity values until the spacecraft exits the potential structure's flux tube. The data indicate that the auroral density cavity is not confined by the potential structure and may extend above the auroral acceleration region.

  • 297.
    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, Centra, 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 selection2021Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 504, nr 2, s. 2822-2831Artikel i tidskrift (Refereegranskat)
    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.

  • 298.
    Alp, Dennis
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    An X-Ray View of Core-collapse Supernovae2021Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    En kärnkollapssupernova (CCSN) är en astronomisk explosion som indikerar slutet av en massiv stjärnas liv. Från observationer är det tydligt att en stor andel av alla massiva stjärnor exploderar som supernovor (SN:or), men att förklara hur SN:or exploderar har kvarstått som en utmaning under flera decennier. En viktig del av pusslet är föregångarstjärnans egenskaper.

    De bifogade artiklarna fokuserar på att jämföra teoretiska förutsägelser med observationer, primärt observationer av SN 1987A. Det är den närmsta observerade SN:an på över fyra århundraden, vilket möjliggör mer detaljerade studier än av någon annan SN. Artiklarna studerar olika aspekter av SN-fenomenet. Studierna är observationellt vitt skilda men adresserar alla frågor som är viktiga för vår förståelse av SN-processen.

    Föregångarstjärnans egenskaper är avgörande för den efterföljande SN-explosionen. Paper III jämför modeller baserade på olika föregångarstjärnor med tidiga röntgen- och gamma-observationer av SN 1987A. Resultaten från studien begränsar föregångarstjärnans utveckling. I Paper IV söker vi SN chockutbrott (SBO:s), vilka är de första elektromagnetiska signalerna från CCSN:or. De upptäckta kandidaterna bär information om föregångarstjärnorna, testar SBO-teorin, och indikerar förekomsten av andra typer av röntgentransienter.

    Själva SN-explosionsmekanismen är också kritisk för analysen i Paper III. Explosionsmodellerna som används i Paper III baseras på några av de senaste tre-dimensionella neutrinodrivna SN-modellerna. Resultaten ger ytterligare stöd för hypotesen att fördröjd neutrinoupphettning är tillräcklig för att explodera den överväldigande majoriteten av alla CCSN:or.

    SN-rester ger också mycket information om SN-explosioner. Kvarlevorna av den centrala kärnan, det kompakta objektet, i SN 1987A har ännu inte blivit detekterad. Vi har undersökt hur ett kompakt objekt kan förbli dolt i ejektat i Paper I, med hjälp av en absorptionsmodell från Paper II. Den mest troliga förklaringen är att neutronstjärnan är passiv, stoftskymd, och bara har en termisk emissionskomponent. Paper V är ytterligare en studie av SN 1987A, men som specifikt fokuserar på röntgenemissionen som uppstår då ejektat interagerar med det cirkumstellära mediet (CSM:et). Röntgenstrålningen är primärt producerad av termiska processer i kollisionen mellan ejektat och CSM:et. Vi fann inget stöd för något bidrag från relativistiska partiklar eller en neutronstjärna.

    Vår beskrivning av CCSN:or förbättras kontinuerligt men många frågor är ännu obesvarade. Framtida observationer kommer ge nya ledtrådar och de modeller vi har studerat kan användas för fortsatta analyser. Nästa generations röntgenteleskop kommer vara väldigt kraftfulla och en galaktisk SN, som skulle vara mycket värdefull för hela forskningsfältet, kan ske när som helst.

    Ladda ner fulltext (pdf)
    alp_phd_public.pdf
  • 299.
    Alp, Dennis
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Core-collapse Supernovae: Theory vs. Observations2019Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    En kärnkollapssupernova (CCSN) är en astronomisk explosion som indikerar slutet av en massiv stjärnas liv. Stjärnans järnkärna kollapsar antingen till en neutronstjärna eller ett svart hål medan resten av materialet slungas iväg med höga hastigheter. Supernovor (SNe) är viktiga för Universums kemiska utveckling eftersom en stor andel av alla tyngre element såsom syre, kisel, och järn frigörs i CCSN-explosioner. Ytterligare en viktig roll för SNe är att nästa generations stjärnor och planeter bildas av det utkastade materialet. Från observationer är det tydligt att en stor andel av alla massiva stjärnor genomgår SN-explosioner, men att förklara hur SNe exploderar har kvarstått som en utmaning under flera decennier.

    De bifogade artiklarna fokuserar på att jämföra teoretiska förutsägelser med observationer, primärt observationer av SN 1987A. Det kompakta objektet i SN 1987A har ännu inte blivit detekterat och vi har undersökt hur ett kompakt objekt kan förbli dolt i ejektat (Paper I och II). De direkta röntgenobservationerna är inte så begränsande även längs potentiellt gynsamma siktlinjer på grund av det metallrika ejektats höga opacitet. Däremot begränsar kombinationen av alla observationer starkt ackretion och sätter en gräns för möjlig pulsarvindsaktivitet. Den termiska ytstrålningen från en neutronstjärna är konsistent med observationerna om vår siktlinje är skymd av stoft, och bara marginellt konsistent annars. Framtida observationer utgör lovande möjligheter för att detektera det kompakta objektet.

    Vi har också jämfört de senaste tredimensionella neutrinodrivna SN-modellerna, som är baserade på explosionssimuleringar, med tidiga röntgen- och gamma-observationer av SN 1987A (Paper III). SN 1987A-modellerna passar datan väl, men alla diskrepanser kan inte förklaras av ett lämpligt val av observationsvinkel. Generellt så påverkar inte asymmetrierna den tidiga emissionen kvalitativt och olika föregångarstjärnor av samma kategori resulterar i likartad strålning. Vi finner också att föregångarstjärnans metallisitet är viktig för egenskaperna av lågenergiröntgenstrålningen. Befintliga instrument borde kunna detektera denna emission på 3--10 Mpc, vilket motsvarar avstånd lite bortom den Lokala galaxhopen.

    Ladda ner fulltext (pdf)
    fulltext
  • 300.
    Alp, Dennis
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Early X-Ray and Gamma-Ray Emission from 3D Neutrino-Driven SN Simulations and Comparisons With Observations of SN 1987AManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    During the first few hundred days, core-collapse supernovae (CCSNe) strongly emit X-rays and gamma-rays originating from radioactive elements, primarily the 56Ni chain. We use SN models based on three-dimensional (3D) neutrino-driven explosion simulations to compute this early emission and compare the predictions to observations of SN 1987A. The agreement between the models and observations is good but small differences that cannot be matched by a suitable choice of viewing angle are evident. The discrepancies indicate that the models need to be slightly more mixed and the bulk of the 56Ni should be moving away from us at higher velocities than can be found in the models. Asymmetries and 3D structures vary the flux by a factor of a few but do not affect the emission qualitatively. The emission also shows similar properties for qualitatively similar progenitors. The only major difference is that stripped-envelope SNe evolve faster and are more than an order of magnitude more luminous. The soft X-ray cutoff is primarily determined by the metallicity of the progenitor. Future NuSTAR observations should detect the down-scattered continuum and low-energy cutoff of (non-)stripped SNe at distances of (3)10 Mpc. INTEGRAL/SPI can detect the direct line emission at distances of (0.2)2 Mpc.

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