Spectral components in the bright, long GRB 061007: properties of the photosphere and the nature of the outflow

Authors

  • J. Larsson,

    Corresponding author
    1. Department of Astronomy, Stockholm University, SE-106 91 Stockholm, Sweden
    2. The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova, SE-106 91 Stockholm, Sweden
      E-mail: josefin.larsson@astro.su.se
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  • F. Ryde,

    1. The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova, SE-106 91 Stockholm, Sweden
    2. Department of Physics, Royal Institute of Technology (KTH), AlbaNova, SE-106 91 Stockholm, Sweden
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  • C. Lundman,

    1. The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova, SE-106 91 Stockholm, Sweden
    2. Department of Physics, Royal Institute of Technology (KTH), AlbaNova, SE-106 91 Stockholm, Sweden
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  • S. McGlynn,

    1. The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova, SE-106 91 Stockholm, Sweden
    2. Department of Physics, Royal Institute of Technology (KTH), AlbaNova, SE-106 91 Stockholm, Sweden
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  • S. Larsson,

    1. Department of Astronomy, Stockholm University, SE-106 91 Stockholm, Sweden
    2. The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova, SE-106 91 Stockholm, Sweden
    3. Department of Physics, Royal Institute of Technology (KTH), AlbaNova, SE-106 91 Stockholm, Sweden
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  • M. Ohno,

    1. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5120, Japan
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  • K. Yamaoka

    1. Department of Physics and Mathematics, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan
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E-mail: josefin.larsson@astro.su.se

ABSTRACT

We present a time-resolved spectral analysis of the bright, long GRB 061007 (z= 1.261) using Swift and Suzaku data. We find that the prompt emission of the burst can be equally well explained by a photospheric component together with a power law as by a Band function, and we explore the implications of the former model. The photospheric component, which we model with a multicolour blackbody, dominates the spectra and has a very stable shape throughout the burst. This component provides a natural explanation for the hardness–intensity correlation seen within the burst and also allows us to estimate the bulk Lorentz factor and the radius of the photosphere. The power-law component dominates the fit at high energies and has a nearly constant slope of −1.5. We discuss the possibility that this component is of the same origin as the high-energy power laws recently observed in some Fermi bursts.

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