Accretion geometry of the neutron star low mass X-ray binary Cyg X-2 from X-ray polarization measurements

  • R Farinelli
    INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna , Via P. Gobetti 101, I-40129 Bologna, Italy
  • S Fabiani
    INAF – IAPS , via del Fosso del Cavaliere 100, I-00113 Roma, Italy
  • J Poutanen
    Department of Physics and Astronomy , FI-20014 University of Turku, Finland
  • F Ursini
    Dipartimento di Matematica e Fisica, Università degli Studi Roma Tre , Via della Vasca Navale 84, I-00146 Roma, Italy
  • C Ferrigno
    Department of Astronomy, University of Geneva , Ch. d’Ecogia 16, CH-1290 Versoix, Geneva, Switzerland
  • S Bianchi
    Dipartimento di Matematica e Fisica, Università degli Studi Roma Tre , Via della Vasca Navale 84, I-00146 Roma, Italy
  • M Cocchi
    INAF – Osservatorio Astronomico di Cagliari , via della Scienza 5, I-09047 Selargius (CA), Italy
  • F Capitanio
    INAF – IAPS , via del Fosso del Cavaliere 100, I-00113 Roma, Italy
  • A De Rosa
    INAF – IAPS , via del Fosso del Cavaliere 100, I-00113 Roma, Italy
  • A Gnarini
    Dipartimento di Matematica e Fisica, Università degli Studi Roma Tre , Via della Vasca Navale 84, I-00146 Roma, Italy
  • F Kislat
    University of New Hampshire, Department of Physics & Astronomy and Space Science Center , 8 College Rd, Durham, NH 03824, USA
  • G Matt
    Dipartimento di Matematica e Fisica, Università degli Studi Roma Tre , Via della Vasca Navale 84, I-00146 Roma, Italy
  • R Mikusincova
    Dipartimento di Matematica e Fisica, Università degli Studi Roma Tre , Via della Vasca Navale 84, I-00146 Roma, Italy
  • F Muleri
    INAF – IAPS , via del Fosso del Cavaliere 100, I-00113 Roma, Italy
  • I Agudo
    Instituto de Astrofísica de Andalucía-CSIC , Glorieta de la Astronomía s/n, E-18008 Granada, Spain
  • L A Antonelli
    INAF Osservatorio Astronomico di Roma , Via Frascati 33, I-00078 Monte Porzio Catone (RM), Italy
  • M Bachetti
    INAF – Osservatorio Astronomico di Cagliari , via della Scienza 5, I-09047 Selargius (CA), Italy
  • L Baldini
    Istituto Nazionale di Fisica Nucleare , Sezione di Pisa, Largo B. Pontecorvo 3, I-56127 Pisa, Italy
  • W H Baumgartner
    NASA Marshall Space Flight Center , Huntsville, AL 35812, USA
  • R Bellazzini
    Istituto Nazionale di Fisica Nucleare , Sezione di Pisa, Largo B. Pontecorvo 3, I-56127 Pisa, Italy
  • S D Bongiorno
    NASA Marshall Space Flight Center , Huntsville, AL 35812, USA
  • R Bonino
    Istituto Nazionale di Fisica Nucleare , Sezione di Torino, Via Pietro Giuria 1, I-10125 Torino, Italy
  • A Brez
    Istituto Nazionale di Fisica Nucleare , Sezione di Pisa, Largo B. Pontecorvo 3, I-56127 Pisa, Italy
  • N Bucciantini
    INAF Osservatorio Astrofisico di Arcetri , Largo Enrico Fermi 5, I-50125 Firenze, Italy
  • S Castellano
    Istituto Nazionale di Fisica Nucleare , Sezione di Pisa, Largo B. Pontecorvo 3, I-56127 Pisa, Italy
  • E Cavazzuti
    ASI - Agenzia Spaziale Italiana , Via del Politecnico snc, I-00133 Roma, Italy
  • S Ciprini
    Space Science Data Center, Agenzia Spaziale Italiana , Via del Politecnico snc, I-00133 Roma, Italy
  • E Costa
    INAF – IAPS , via del Fosso del Cavaliere 100, I-00113 Roma, Italy
  • E Del Monte
    INAF – IAPS , via del Fosso del Cavaliere 100, I-00113 Roma, Italy
  • L Di Gesu
    ASI - Agenzia Spaziale Italiana , Via del Politecnico snc, I-00133 Roma, Italy
  • N Di Lalla
    Department of Physics and Kavli Institute for Particle Astrophysics and Cosmology, Stanford University , Stanford, California 94305, USA
  • A Di Marco
    INAF – IAPS , via del Fosso del Cavaliere 100, I-00113 Roma, Italy
  • I Donnarumma
    ASI - Agenzia Spaziale Italiana , Via del Politecnico snc, I-00133 Roma, Italy
  • V Doroshenko
    Institut für Astronomie und Astrophysik, Universität Tübingen , Sand 1, D-72076 Tübingen, Germany
  • M Dovčiak
    Astronomical Institute of the Czech Academy of Sciences , Boční II 1401/1, 14100 Praha 4, Czech Republic
  • S R Ehlert
    NASA Marshall Space Flight Center , Huntsville, AL 35812, USA
  • T Enoto
    RIKEN Cluster for Pioneering Research , 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
  • Y Evangelista
    INAF – IAPS , via del Fosso del Cavaliere 100, I-00113 Roma, Italy
  • R Ferrazzoli
    INAF – IAPS , via del Fosso del Cavaliere 100, I-00113 Roma, Italy
  • J A Garcia
    California Institute of Technology , Pasadena, CA 91125, USA
  • S Gunji
    Yamagata University , 1-4-12 Kojirakawa-machi, Yamagata-shi 990-8560, Japan
  • K Hayashida
    Osaka University , 1-1 Yamadaoka, Suita, Osaka 565-0871, Japan
  • J Heyl
    University of British Columbia , Vancouver, BC V6T 1Z4, Canada
  • W Iwakiri
    Department of Physics, Faculty of Science and Engineering , Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan
  • S G Jorstad
    Institute for Astrophysical Research, Boston University , 725 Commonwealth Avenue, Boston, MA 02215, USA
  • V Karas
    Astronomical Institute of the Czech Academy of Sciences , Boční II 1401/1, 14100 Praha 4, Czech Republic
  • T Kitaguchi
    RIKEN Cluster for Pioneering Research , 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
  • J J Kolodziejczak
    NASA Marshall Space Flight Center , Huntsville, AL 35812, USA
  • H Krawczynski
    Physics Department and McDonnell Center for the Space Sciences, Washington University in St. Louis, St. Louis , MO 63130, USA
  • F La Monaca
    INAF – IAPS , via del Fosso del Cavaliere 100, I-00113 Roma, Italy
  • L Latronico
    Istituto Nazionale di Fisica Nucleare , Sezione di Torino, Via Pietro Giuria 1, I-10125 Torino, Italy
  • I Liodakis
    Finnish Centre for Astronomy with ESO , FI-20014 University of Turku, Finland
  • S Maldera
    Istituto Nazionale di Fisica Nucleare , Sezione di Torino, Via Pietro Giuria 1, I-10125 Torino, Italy
  • A Manfreda
    Istituto Nazionale di Fisica Nucleare , Sezione di Pisa, Largo B. Pontecorvo 3, I-56127 Pisa, Italy
  • F Marin
    Université de Strasbourg , CNRS, Observatoire Astronomique de Strasbourg, UMR 7550, F-67000 Strasbourg, France
  • A P Marscher
    Institute for Astrophysical Research, Boston University , 725 Commonwealth Avenue, Boston, MA 02215, USA
  • H L Marshall
    MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, MA 02139, USA
  • I Mitsuishi
    Graduate School of Science, Division of Particle and Astrophysical Science, Nagoya University , Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan
  • T Mizuno
    Hiroshima Astrophysical Science Center, Hiroshima University , 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan
  • C-Y Ng
    Department of Physics, The University of Hong Kong , Pokfulam, Hong Kong
  • S L O’Dell
    NASA Marshall Space Flight Center , Huntsville, AL 35812, USA
  • N Omodei
    Department of Physics and Kavli Institute for Particle Astrophysics and Cosmology, Stanford University , Stanford, California 94305, USA
  • C Oppedisano
    Istituto Nazionale di Fisica Nucleare , Sezione di Torino, Via Pietro Giuria 1, I-10125 Torino, Italy
  • A Papitto
    INAF Osservatorio Astronomico di Roma , Via Frascati 33, I-00078 Monte Porzio Catone (RM), Italy
  • G G Pavlov
    Department of Astronomy and Astrophysics, Pennsylvania State University , University Park, PA 16802, USA
  • A L Peirson
    Department of Physics and Kavli Institute for Particle Astrophysics and Cosmology, Stanford University , Stanford, California 94305, USA
  • M Perri
    INAF Osservatorio Astronomico di Roma , Via Frascati 33, I-00078 Monte Porzio Catone (RM), Italy
  • M Pesce-Rollins
    Istituto Nazionale di Fisica Nucleare , Sezione di Pisa, Largo B. Pontecorvo 3, I-56127 Pisa, Italy
  • P O Petrucci
    Université Grenoble Alpes , CNRS, IPAG, F-38000 Grenoble, France
  • M Pilia
    INAF – Osservatorio Astronomico di Cagliari , via della Scienza 5, I-09047 Selargius (CA), Italy
  • A Possenti
    INAF – Osservatorio Astronomico di Cagliari , via della Scienza 5, I-09047 Selargius (CA), Italy
  • S Puccetti
    Space Science Data Center, Agenzia Spaziale Italiana , Via del Politecnico snc, I-00133 Roma, Italy
  • B D Ramsey
    NASA Marshall Space Flight Center , Huntsville, AL 35812, USA
  • J Rankin
    INAF – IAPS , via del Fosso del Cavaliere 100, I-00113 Roma, Italy
  • A Ratheesh
    INAF – IAPS , via del Fosso del Cavaliere 100, I-00113 Roma, Italy
  • R W Romani
    Department of Physics and Kavli Institute for Particle Astrophysics and Cosmology, Stanford University , Stanford, California 94305, USA
  • C Sgrò
    Istituto Nazionale di Fisica Nucleare , Sezione di Pisa, Largo B. Pontecorvo 3, I-56127 Pisa, Italy
  • P Slane
    Center for Astrophysics, Harvard & Smithsonian , 60 Garden St, Cambridge, MA 02138, USA
  • P Soffitta
    INAF – IAPS , via del Fosso del Cavaliere 100, I-00113 Roma, Italy
  • G Spandre
    Istituto Nazionale di Fisica Nucleare , Sezione di Pisa, Largo B. Pontecorvo 3, I-56127 Pisa, Italy
  • T Tamagawa
    RIKEN Cluster for Pioneering Research , 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
  • F Tavecchio
    INAF Osservatorio Astronomico di Brera , Via E. Bianchi 46, I-23807 Merate (LC), Italy
  • R Taverna
    Dipartimento di Fisica e Astronomia, Università degli Studi di Padova , Via Marzolo 8, I-35131 Padova, Italy
  • Y Tawara
    Graduate School of Science, Division of Particle and Astrophysical Science, Nagoya University , Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan
  • A F Tennant
    NASA Marshall Space Flight Center , Huntsville, AL 35812, USA
  • N E Thomas
    NASA Marshall Space Flight Center , Huntsville, AL 35812, USA
  • F Tombesi
    Istituto Nazionale di Fisica Nucleare , Sezione di Roma ‘Tor Vergata’, Via della Ricerca Scientifica 1, I-00133 Roma, Italy
  • A Trois
    INAF – Osservatorio Astronomico di Cagliari , via della Scienza 5, I-09047 Selargius (CA), Italy
  • S S Tsygankov
    Department of Physics and Astronomy , FI-20014 University of Turku, Finland
  • R Turolla
    Dipartimento di Fisica e Astronomia, Università degli Studi di Padova , Via Marzolo 8, I-35131 Padova, Italy
  • J Vink
    Anton Pannekoek Institute for Astronomy & GRAPPA, University of Amsterdam , Science Park 904, NL-1098 XH Amsterdam, The Netherlands
  • M C Weisskopf
    NASA Marshall Space Flight Center , Huntsville, AL 35812, USA
  • K Wu
    Mullard Space Science Laboratory, University College London , Holmbury St Mary, Dorking, Surrey RH5 6NT, UK
  • F Xie
    INAF – IAPS , via del Fosso del Cavaliere 100, I-00113 Roma, Italy
  • S Zane
    Mullard Space Science Laboratory, University College London , Holmbury St Mary, Dorking, Surrey RH5 6NT, UK

抄録

<jats:title>ABSTRACT</jats:title> <jats:p>We report spectro-polarimetric results of an observational campaign of the bright neutron star low-mass X-ray binary Cyg X-2 simultaneously observed by IXPE, NICER, and INTEGRAL. Consistently with previous results, the broad-band spectrum is characterized by a lower-energy component, attributed to the accretion disc with kTin ≈ 1 keV, plus unsaturated Comptonization in thermal plasma with temperature kTe = 3 keV and optical depth τ ≈ 4, assuming a slab geometry. We measure the polarization degree in the 2–8 keV band P = 1.8 ± 0.3 per cent and polarization angle ϕ = 140° ± 4°, consistent with the previous X-ray polarimetric measurements by OSO-8 as well as with the direction of the radio jet which was earlier observed from the source. While polarization of the disc spectral component is poorly constrained with the IXPE data, the Comptonized emission has a polarization degree P = 4.0 ± 0.7 per cent and a polarization angle aligned with the radio jet. Our results strongly favour a spreading layer at the neutron star surface as the main source of the polarization signal. However, we cannot exclude a significant contribution from reflection off the accretion disc, as indicated by the presence of the iron fluorescence line.</jats:p>

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